JP7811162B2 - Grease composition and method for producing grease composition - Google Patents

Description

The present invention relates to a grease composition and a method for producing a grease composition.

Grease is a semi-solid lubricant made by dispersing a solid, highly lipophilic thickener in a base oil. Grease adheres more easily to lubricated parts and is less likely to leak out than lubricating oil. Therefore, using grease can simplify the mechanical structure of the lubrication system. Grease also leaks less than lubricating oil, creating a cleaner environment, and the replenishment interval can be shortened compared to lubricating oil.
Grease is mainly used to lubricate machine elements such as rolling bearings, plain bearings, ball screws, linear guides, and gears. Rolling bearings are widely used in machine tool spindles, railroad car carriages, engine accessories such as automobile alternators, constant velocity joints, wheels, etc.

In response to recent demands for energy conservation and higher efficiency, there is a demand for bearings that can reduce torque.
For example, Patent Document 1 discloses a grease composition in which the relative surface area of a thickener calculated from the particle size distribution of the thickener measured by laser diffraction is equal to or greater than a specific value, and discloses that the grease composition can reduce torque caused by stirring resistance.

Japanese Patent Application Laid-Open No. 2016-204623

Demands for energy savings and higher efficiency are increasing, and a higher level of torque reduction is required than with conventional grease compositions such as those described in Patent Document 1.

The present invention was made in consideration of the above circumstances, and aims to provide a low-torque grease composition and a method for producing said grease composition.

In order to solve the above problems, the present invention employs the following configuration.
[1] A grease composition containing a base oil (A) and a thickener (B), wherein 2 g of the grease composition is sealed in a 6204 ball bearing, and the ball bearing is rotated at a speed of 2000 rpm under atmospheric pressure at 25°C for a predetermined time. When the amount of the grease composition adhering to the bearing balls in the ball bearing is measured using neutron observation, the ratio of the amount of the grease composition adhering to the bearing balls one minute after the start of rotation to the amount of the grease composition adhering to the bearing balls before the start of rotation is 70% or more and 140% or less.
[2] The grease composition according to [1], wherein the ratio of the amount of the grease composition adhering to the bearing balls 60 minutes after the start of rotation to the amount of the grease composition adhering to the bearing balls 1 minute after the start of rotation is 165% or less.
[3] The grease composition according to [1] or [2], wherein the amount of the grease composition adhering to the bearing balls 60 minutes after the start of rotation is 2.00×10 ¹⁰ μm ³ or more and 6.20×10 ¹⁰ μm ³ or less.
[4] The grease composition according to any one of [1] to [3], wherein the thickener (B) comprises one or more thickeners (B1) selected from metal complex soaps and urea compounds.
[5] A method for producing a grease composition according to any one of [1] to [4], comprising: a preparation step of preparing a synthetic material (B0) for synthesizing the thickener (B); a synthesis step of reacting the synthetic material (B0) in the base oil (A) to synthesize the thickener (B); a mixing step of mixing the synthesized thickener (B) with the base oil (A); and a kneading step of kneading the mixture obtained in the mixing step.

The present invention provides a low-torque grease composition and a method for producing the grease composition.

2 is a schematic diagram for explaining the behavior of the grease composition of the present embodiment when a 6204 ball bearing is rotated. FIG. 1 is a schematic diagram for explaining the behavior of a conventional grease composition when a 6204 ball bearing is rotated. FIG. 1 is a schematic diagram for explaining a 6204 ball bearing. 1 shows image analysis data used to measure the amount of the grease composition of Example 1 adhering to the bearing balls before the start of rotation. 1 shows image analysis data used to measure the amount of the grease composition of Example 1 adhering to the bearing balls 60 minutes after the start of rotation. 1 shows image analysis data used to measure the amount of the grease composition of Comparative Example 1 adhering to the bearing balls before the start of rotation. 1 shows image analysis data used to measure the amount of the grease composition of Comparative Example 1 adhering to the bearing balls 60 minutes after the start of rotation. 1 shows image analysis data used to measure the amount of the grease composition of Example 2 adhering to the bearing balls before the start of rotation. 1 shows image analysis data used to measure the amount of the grease composition of Example 2 adhering to the bearing balls 60 minutes after the start of rotation. 1 shows image analysis data used to measure the amount of the grease composition of Comparative Example 2 adhering to the bearing balls before the start of rotation. 1 shows image analysis data used to measure the amount of the grease composition of Comparative Example 2 adhering to the bearing balls 60 minutes after the start of rotation. 1 shows image analysis data used to measure the amount of the grease composition of Comparative Example 3 adhering to the bearing balls before the start of rotation. 1 shows image analysis data used to measure the amount of the grease composition of Comparative Example 3 adhering to the bearing balls 60 minutes after the start of rotation.

(Grease composition)
The grease composition of the present embodiment contains a base oil (A) and a thickener (B).
In the grease composition of this embodiment, 2 g of the grease composition is sealed in a 6204 ball bearing, and the ball bearing is rotated at a speed of 2000 rpm under atmospheric pressure at 25°C for a predetermined period of time. When the amount of the grease composition adhered to the bearing balls in the ball bearing is measured using neutrons, the ratio (hereinafter referred to as "1 min adhesion amount") of the amount of the grease composition adhered to the bearing balls 1 minute after the start of rotation (hereinafter referred to as "1 min adhesion amount") to the amount of the grease composition adhered to the bearing balls before the start of rotation (hereinafter referred to as "0 min adhesion amount") (hereinafter referred to as "1 min adhesion amount/0 min adhesion amount") is 70% or more and 140% or less.

The grease composition of this embodiment has a 1 min adhesion amount/0 min adhesion amount of 70% or more, preferably 80% or more, more preferably 85% or more, and even more preferably 90% or more.
On the other hand, the grease composition of this embodiment has a 1 min adhesion amount/0 min adhesion amount of 140% or less, preferably 138% or less, more preferably 135% or less, and even more preferably 130% or less.

If the 1 min adhesion amount/0 min adhesion amount of the grease composition of this embodiment is 70% or more, the bearing torque can be reduced. If the 1 min adhesion amount/0 min adhesion amount of the grease composition of this embodiment is equal to or greater than the above-mentioned preferable lower limit, the bearing torque can be further reduced.
If the 1 min adhesion amount/0 min adhesion amount of the grease composition of this embodiment is 140% or less, the resistance of the grease composition of this embodiment during bearing rotation can be suppressed and bearing torque can be reduced. If the 1 min adhesion amount/0 min adhesion amount of the grease composition of this embodiment is not more than the above-mentioned preferable upper limit value, bearing torque can be further reduced.

For example, the grease composition of this embodiment preferably has a 1 min adhesion amount/0 min adhesion amount of 80% or more and 138% or less, more preferably 85% or more and 135% or less, and even more preferably 90% or more and 130% or less.

The mechanism by which the grease composition of this embodiment reduces bearing torque will be described with reference to FIGS. 1 and 2.
FIG. 1 is a schematic diagram for explaining the behavior of the grease composition of this embodiment when a 6204 ball bearing is rotated.
If the 1 min adhesion amount/0 min adhesion amount is 70% or more and 140% or less, the grease composition will maintain a moderate adhesion state to the bearing balls in the ball bearing, and the effect of using the grease composition will be fully obtained. In addition, it is presumed that the resistance (stirring resistance) received from the grease composition when the bearing balls rotate can be suppressed, thereby reducing bearing torque.
On the other hand, although not shown, if the 1 min adhesion amount/0 min adhesion amount is less than 70%, this means that the amount of grease composition adhering to the bearing balls decreases significantly after rotation, and two cases are expected: one where the amount of grease composition adhering to the bearing balls before and after rotation is small, and the other where it is large. In the former case, the resistance received from the grease composition when the bearing balls rotate can be suppressed, but the lubricating effect of the grease composition is not fully obtained, which is presumed to cause metal contact within the bearing and increase bearing torque. In the latter case, an excessive amount of grease composition is present near the bearing balls in the ball bearing, which is presumed to increase the resistance received from the grease composition when the bearing balls rotate, which is presumed to increase bearing torque.
Furthermore, as shown in Figure 2, when the 1 min adhesion amount/0 min adhesion amount ratio exceeds 140%, an excessive amount of grease composition continues to remain near the bearing balls inside the ball bearing, which increases the resistance that the bearing balls receive from the grease composition when they rotate, and is presumed to increase the bearing torque.

In this embodiment, 2 g of the grease composition is packed into a 6204 ball bearing, and the ball bearing is rotated at 2000 rpm under atmospheric pressure at 25°C for a predetermined period of time. The amount of grease composition adhered to the bearing balls in the ball bearing is then measured using neutrons. The ratio of the amount of grease composition adhered to the bearing balls 60 minutes after the start of rotation (hereinafter referred to as the "60-min adhesion amount") to the amount adhered in 1 minute (hereinafter referred to as the "60-min adhesion amount/1-min adhesion amount") is preferably 165% or less, more preferably 160% or less, and even more preferably 158% or less.

When the 60-minute adhesion amount/1-minute adhesion amount of the grease composition of this embodiment is equal to or less than the above-mentioned preferred upper limit, the resistance experienced by the bearing balls from the grease composition as they rotate is further reduced, enabling further reduction in bearing torque.

Generally, the longer a ball bearing is rotated, the greater the amount of grease composition that adheres to the bearing balls. Therefore, the lower limit of the 60-minute adhesion amount/1-minute adhesion amount for the grease composition of this embodiment is not particularly limited, but is preferably 90% or more, more preferably 100% or more, and even more preferably 110% or more.

For example, the grease composition of this embodiment preferably has a 60-minute adhesion amount/1-minute adhesion amount of 90% or more and 165% or less, more preferably 100% or more and 160% or less, and even more preferably 110% or more and 158% or less.

The 0-min adhesion amount of the grease composition of this embodiment is preferably 1.00×10 ¹⁰ μm ³ or more, more preferably 1.20×10 ¹⁰ μm ³ or more, and even more preferably 1.50×10 ¹⁰ μm ³ or more.
The 0-min adhesion amount of the grease composition of this embodiment is preferably 5.00×10 ¹⁰ μm ³ or less, more preferably 4.50×10 ¹⁰ μm ³ or less, and even more preferably 4.00×10 ¹⁰ μm ³ or less.

If the 0-min adhesion amount of the grease composition of this embodiment is equal to or greater than the above-mentioned preferable lower limit, the bearing torque is further reduced.
When the 0 min adhesion weight of the grease composition of this embodiment is equal to or less than the above-mentioned preferable upper limit, the resistance that the bearing balls experience from the grease composition when rotating is further reduced, and the bearing torque is further reduced.

For example, the 0-min adhesion amount of the grease composition of this embodiment is preferably 1.00×10 ¹⁰ μm ³ or more and 5.00×10 ¹⁰ μm ³ or less, more preferably 1.20×10 ¹⁰ μm ³ or more and 4.50×10 ¹⁰ μm ³ or less, and even more preferably 1.50×10 ¹⁰ μm ³ or more and 4.00×10 ¹⁰ μm ³ or less.

The 0-min adhesion amount of the grease composition of this embodiment can be calculated by filling a specific amount in a specific location, as described below, and the value does not change depending on the skill of the person measuring or the filling method. The 0-min adhesion amount of the grease composition of this embodiment changes depending on the physical properties of the grease composition. A method for controlling the 0-min adhesion amount will be described below.

The adhesion amount per minute of the grease composition of this embodiment is preferably 1.80×10 ¹⁰ μm ³ or more, more preferably 2.00×10 ¹⁰ μm ³ or more, and even more preferably 2.20×10 ¹⁰ μm ³ or more.
The adhesion amount per minute of the grease composition of this embodiment is preferably 5.00×10 ¹⁰ μm ³ or less, more preferably 4.50×10 ¹⁰ μm ³ or less, and even more preferably 4.00×10 ¹⁰ μm ³ or less.

If the adhesion weight per minute of the grease composition of this embodiment is equal to or greater than the above-mentioned preferable lower limit, the bearing torque is further reduced.
If the adhesion weight per minute of the grease composition of this embodiment is equal to or less than the above-mentioned preferable upper limit, the resistance that the bearing balls experience from the grease composition when rotating is further reduced, and the bearing torque is further reduced.

For example, the adhesion amount per minute of the grease composition of this embodiment is preferably 1.80×10 ¹⁰ μm ³ or more and 5.00×10 ¹⁰ μm ³ or less, more preferably 2.00×10 ¹⁰ μm ³ or more and 4.50×10 ¹⁰ μm ³ or less, and even more preferably 2.20×10 ¹⁰ μm ³ or more and 4.00×10 ¹⁰ μm ³ or less.

The 60-minute adhesion amount of the grease composition of this embodiment is preferably 2.00×10 ¹⁰ μm ³ or more, more preferably 2.20×10 ¹⁰ μm ³ or more, and even more preferably 2.50×10 ¹⁰ μm ³ or more.
The 60-minute adhesion amount of the grease composition of this embodiment is preferably 6.20×10 ¹⁰ μm ³ or less, more preferably 6.00×10 ¹⁰ μm ³ or less, and even more preferably 5.80×10 ¹⁰ μm ³ or less.

If the 60-minute adhesion weight of the grease composition of this embodiment is equal to or greater than the above-mentioned preferable lower limit, the bearing torque is further reduced.
If the 60-minute adhesion weight of the grease composition of this embodiment is equal to or less than the above-mentioned preferable upper limit, the resistance that the bearing balls experience from the grease composition when rotating is further reduced, and the bearing torque is further reduced.

For example, the 60-minute adhesion amount of the grease composition of this embodiment is preferably 2.00×10 ¹⁰ μm ³ or more and 6.20×10 ¹⁰ μm ³ or less, more preferably 2.20×10 ¹⁰ μm ³ or more and 6.00×10 ¹⁰ μm ³ or less, and even more preferably 2.50×10 ¹⁰ μm ³ or more and 5.80×10 ¹⁰ μm ³ or less.

The 0-minute adhesion weight, 1-minute adhesion weight, and 60-minute adhesion weight of the grease composition of this embodiment can be calculated by a neutron imaging method.
For example, the 0-min adhesion weight, 1-min adhesion weight, and 60-min adhesion weight of the grease composition of this embodiment can be calculated by neutron radiography and computed tomography (CT) measurements of the grease composition distribution in a 6204 ball bearing using RADEN at the Materials and Life Science Experimental Facility (MLF) of the Japan Proton Accelerator Research Complex (J-PARC).

FIG. 3 is a schematic diagram for explaining the 6204 ball bearing 10.
The 6204 ball bearing 10 is composed of an outer ring 7 , an inner ring 5 , bearing balls 3 , and a cage 1 .
The bearing balls 3 are held by a cage 1 between an inner ring 5 and an outer ring 7 at regular intervals so that the eight bearing balls 3 do not come into contact with one another.

The specific procedure for calculating the 0-min adhesion weight, 1-min adhesion weight, and 60-min adhesion weight of the grease composition of this embodiment is as follows.
(i) A sample was prepared by filling 0.25 g (2 g in total) of the grease composition of this embodiment onto each of eight locations on the cage between the bearing balls of a 6204 ball bearing and sealing with a rubber seal.
(ii) The sample is fixed on a rotating stage and irradiated with a neutron beam using the RADEN. The neutrons that pass through the sample are converted into visible light using a 0.10 mm thick ⁶ LiF/ZnS scintillator screen, and the transmission image is then saved using a 2048 x 2048 pixel water-cooled CCD camera. For radiographic observation, neutrons are irradiated in the axial direction of the 6204 ball bearing with a field of view of 80 mm x 80 mm and a camera exposure time of approximately 30 seconds. The spatial resolution of the resulting transmission image is, for example, 60 μm.
(iii) A three-dimensional image is created using filtered back projection from 600 transmission images obtained by rotating the sample from 0° to 360° in 0.6° increments.
(iv) In the three-dimensional image obtained in (iii), the volume ( ^μm3 ) of the grease composition of this embodiment is calculated by image analysis, using a measurement range 1.2 times the diameter of the bearing ball. The 0-min adhesion amount can be calculated from the average volume of the grease composition of this embodiment adhered to the eight bearing balls (the average of the six volumes excluding the minimum and maximum values).
(v) The 1-minute adhesion amount can be calculated by rotating the ball bearing at 2000 rpm under atmospheric pressure at 25°C for 1 minute and then performing the steps (ii) to (iv) above. Also, the 60-minute adhesion amount can be calculated by rotating the ball bearing at 2000 rpm under atmospheric pressure at 25°C for 60 minutes and then performing the steps (ii) to (iv) above.

The 0-min, 1-min, and 60-min adhesion amounts of the grease composition of this embodiment can be controlled by the type and content of the base oil (A) and thickener (B) described below, and the manufacturing conditions of the grease composition. Specific examples of the manufacturing conditions include, when a three-roll mill is used to manufacture the grease composition, the shear force due to the difference in roller speeds and the number of times the material is passed through the three-roll mill. Furthermore, when a hydraulic three-roll mill is used, examples of the manufacturing conditions include the compression force generated by the pressure between the rollers.

The consistency of the grease composition of this embodiment is preferably 190 or more, more preferably 200 or more, and even more preferably 210 or more.
On the other hand, the consistency of the grease composition of this embodiment is preferably 340 or less, more preferably 320 or less, and even more preferably 300 or less.
For example, the consistency of the grease composition of this embodiment is preferably 190 or more and 340 or less, more preferably 200 or more and 320 or less, and even more preferably 210 or more and 300 or less.

When the consistency of the grease composition of this embodiment is equal to or greater than the above-mentioned preferable lower limit, the lubrication properties of the grease composition are improved, and the bearing torque is further reduced.
When the consistency of the grease composition of this embodiment is equal to or less than the above-mentioned preferable upper limit, the viscous resistance caused by the grease composition is reduced, and the bearing torque is further reduced.
In this specification, the consistency refers to worked consistency measured in accordance with JIS K2220:2013.

<Base oil (A)>
The grease composition of the present embodiment contains a base oil (A).
The kinematic viscosity of the base oil (A) at 40°C is preferably 15 mm ² /s or more, more preferably 30 mm ² /s or more.
The kinematic viscosity of the base oil (A) at 40°C is preferably 100 mm ² /s or less, more preferably 70 mm ² /s or less.

When the kinematic viscosity at 40°C of the base oil (A) of the grease composition of this embodiment is equal to or greater than the above-mentioned preferable lower limit, the lubricity of the grease composition is improved, and the bearing torque is further reduced.
When the kinematic viscosity at 40°C of the base oil (A) of the grease composition of this embodiment is equal to or less than the above-mentioned preferable upper limit, the viscous resistance caused by the grease composition is reduced, and the bearing torque is further reduced.

For example, the kinematic viscosity of the base oil (A) at 40° C. is preferably 15 mm ² /s or more and 100 mm ² /s or less, and more preferably 30 mm ² /s or more and 70 mm ² /s or less.

In this specification, the kinematic viscosity at 40°C refers to the kinematic viscosity at 40°C measured in accordance with JIS K2283:2000.

The base oil (A) of the grease composition of this embodiment may be a synthetic oil or a mineral oil.

≪Synthetic oil≫
Examples of synthetic oils include polyolefins such as poly-α-olefins, ester base oils such as diesters and polyol esters, polyalkylene glycols, alkylbenzenes, and alkylnaphthalenes.
As the base oil (A) of the grease composition of this embodiment, a single synthetic oil may be used alone, or a mixture of multiple synthetic oils may be used.

<Mineral oil>
As the mineral oil, a distillate obtained by atmospheric distillation of crude oil can be used. In addition, a lubricating oil fraction obtained by further vacuum distillation of the distillate obtained by the atmospheric distillation and then refining the distillate through various refining processes can also be used.
The refining process may be a suitable combination of hydrorefining, solvent extraction, solvent dewaxing, hydrodewaxing, sulfuric acid washing, clay treatment, etc. Mineral oil can be obtained by combining these refining processes in a suitable order.
Furthermore, a mixture of a plurality of refined oils with different properties obtained by subjecting different crude oils or distillate oils to a combination of different refining processes may also be used.

As the mineral oil, a Group I base oil (hereinafter referred to as "API Group I base oil"), a Group II base oil (hereinafter referred to as "API Group II base oil"), or a Group III base oil (hereinafter referred to as "API Group III base oil") of the API base oil classification, or a mixture thereof, can be used.
API Group I base oils are mineral base oils having a sulfur content greater than 0.03 wt.% and/or a saturates content less than 90 wt.% and a viscosity index greater than or equal to 80 and less than 120.
API Group II base oils are mineral base oils having a sulfur content of 0.03 wt.% or less, a saturates content of 90 wt.% or more, and a viscosity index of 80 or more but less than 120.
API Group III base oils are mineral base oils having a sulfur content of 0.03 wt.% or less, a saturates content of 90 wt.% or more, and a viscosity index of 120 or more.

The base oil (A) of the grease composition of this embodiment may be a single mineral oil, or a mixture of multiple mineral oils. In a mixed base oil containing multiple mineral oils, the API classifications of the mineral oils may be the same or different from each other.

The base oil (A) of the grease composition of this embodiment may be either a mineral oil or a synthetic oil, or a mixture of a mineral oil and a synthetic oil.

The content of the base oil (A) in the grease composition of this embodiment is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 80% by mass or more, based on the total amount of the grease composition.
The content of the base oil (A) in the grease composition of this embodiment is preferably 95 mass % or less, and more preferably 90 mass % or less, based on the total amount of the grease composition.
For example, the content of the base oil (A) in the grease composition of the present embodiment is preferably 50% by mass or more and 95% by mass or less, more preferably 60% by mass or more and 95% by mass or less, and even more preferably 80% by mass or more and 90% by mass or less, based on the total amount of the grease composition.

When the content of base oil (A) in the grease composition of this embodiment is within the above preferred range, it becomes easier to control the 1-min adhesion amount/0-min adhesion amount in the grease composition to 70% or more and 140% or less.

<Thickener (B)>
The grease composition of the present embodiment contains a thickener (B).
The thickener (B) is preferably one or more thickeners (B1) (hereinafter also referred to as "component (B1)") selected from metal complex soaps and urea compounds.

<Metal Complex Soap>
Metal complex soap is a metal soap made by saponifying and compounding carboxylic acids of different molecular structures with metal hydroxides.
Specific examples of the metal complex soap include metal complex soaps obtained by reacting a metal hydroxide with a fatty acid and a dibasic acid or an aromatic carboxylic acid.
Examples of the metal in the metal complex soap include alkali metals such as lithium and sodium, alkaline earth metals such as calcium, and amphoteric metals such as aluminum. Of the above, lithium and aluminum are preferred, with lithium being more preferred, from the viewpoint of further reducing bearing torque.

The fatty acid may be a fatty acid derivative having a substituent such as a hydroxy group.
The fatty acid is preferably a monovalent or divalent fatty acid.
The fatty acid is preferably a fatty acid having 6 to 20 carbon atoms, more preferably a monovalent fatty acid having 12 to 20 carbon atoms or a divalent fatty acid having 6 to 14 carbon atoms. In the present invention, "6 to 20 carbon atoms" means having 6 or more and 20 or less carbon atoms.

Among the above, the fatty acid is preferably a monovalent fatty acid containing one hydroxy group.
Examples of dibasic acids to be combined with fatty acids in metal complex soaps include acetic acid, azelaic acid, and sebacic acid.
Examples of aromatic carboxylic acids to be combined with fatty acids in metal complex soaps include benzoic acid.

Among the above metal complex soaps, preferred are lithium complex soaps obtained by reacting lithium hydroxide with a monovalent fatty acid having 6 to 20 carbon atoms and containing one hydroxy group and a dibasic acid, more preferred are lithium complex soaps obtained by reacting lithium hydroxide with a monovalent fatty acid having 12 to 20 carbon atoms and containing one hydroxy group and azelaic acid, and even more preferred are lithium complex soaps obtained by reacting lithium hydroxide with 12-hydroxystearic acid and azelaic acid.

As the metal complex soap in the grease composition of this embodiment, one type of metal complex soap may be used alone, or multiple metal complex soaps may be mixed and used.

<Urea-based thickener>
Examples of the urea-based thickener include diurea compounds and polyurea compounds.
A diurea compound is a compound obtained by reacting a diisocyanate with a monoamine, and has two urea groups (—NH—CO—NH—).
In this specification, the polyurea compound refers to a compound obtained by reacting a diisocyanate with a monoamine or diamine, and having three or more urea groups (—NH—CO—NH—).

Diisocyanates Diisocyanates are compounds in which two hydrogen atoms of a hydrocarbon are replaced with an isocyanate group (-N=C=O).
The hydrocarbon may be a cyclic hydrocarbon or a chain hydrocarbon, and may be an aromatic hydrocarbon or an aliphatic hydrocarbon.
The hydrocarbon preferably has 4 to 20 carbon atoms, more preferably 8 to 18 carbon atoms.

Specific preferred examples of diisocyanates include phenylene diisocyanate, tolylene diisocyanate, biphenyl diisocyanate (diphenyl diisocyanate), diphenylmethane-4,4'-diisocyanate (MDI), octadecane diisocyanate, decane diisocyanate, and hexane diisocyanate.
The diisocyanates may be used alone or in combination of two or more.

-Monoamines Monoamines are compounds that have one amino group per molecule.
Preferred monoamines include octylamine, dodecylamine, hexadecylamine, stearylamine (octadecylamine), oleylamine, aniline, p-toluidine, and cyclohexylamine.
The monoamine may be a cyclic amine or a chain amine, and may also be an alicyclic amine, an aromatic amine, or an aliphatic amine.
The monoamine is preferably a chain amine.
The chain amine preferably has 4 to 20 carbon atoms, more preferably 6 to 16 carbon atoms, and even more preferably 6 to 10 carbon atoms.

- Diamine Diamine is a compound that has two amino groups in one molecule.
Preferred diamines include ethylenediamine, propanediamine, butanediamine, hexanediamine, octanediamine, phenylenediamine, tolylenediamine, xylenediamine, and diaminodiphenylmethane.
The diamine may be a cyclic amine or a chain amine, and may also be an alicyclic amine, an aromatic amine, or an aliphatic amine.
The diamine preferably has 4 to 20 carbon atoms, more preferably 8 to 18 carbon atoms.

Of the above, diurea compounds are preferred as the urea-based thickener.
The diurea compound is preferably a compound obtained by reacting a diisocyanate having an aromatic hydrocarbon group with a monoamine.
As the diisocyanate having an aromatic hydrocarbon group, diphenylmethane-4,4'-diisocyanate (MDI) is preferred.
As the monoamine, an aliphatic amine is preferred from the viewpoint of reducing the coefficient of friction at the contact portion.
Among these, from the viewpoint of reducing excessive flow of the grease composition within the bearing and appropriately controlling the amount of the grease composition adhering to the bearing balls, aliphatic amines having 6 to 16 carbon atoms are more preferred, and aliphatic amines having 6 to 10 carbon atoms are even more preferred.

As the urea-based thickener for the grease composition of this embodiment, one type of urea-based thickener may be used alone, or multiple urea-based thickeners may be used in combination.

Examples of thickeners (B2) (hereinafter also referred to as "component (B2)") other than the above-mentioned component (B1) include the following thickeners:

<<Thickener (B2) Other Than Component (B1)>>
Examples of the component (B2) include single metal soap thickeners and inorganic thickeners.

- Single metal soap thickeners Single metal soap thickeners are single metal soaps obtained by saponifying fatty acids or fats and oils with metal hydroxides.
The fatty acid may be the same as the fatty acid in the metal complex soap described above.

Metals in single metal soap thickeners include alkali metals such as lithium and sodium, alkaline earth metals such as calcium, and amphoteric metals such as aluminum.

Inorganic Thickeners Specific examples of inorganic thickeners include bentonite and silica gel.

The proportion of component (B1) in the thickener (B) of the grease composition of this embodiment is preferably 80 mass % or more, more preferably 90 mass % or more, based on the total amount of thickener (B), and even more preferably 100 mass %, i.e., it is composed solely of component (B1).
In one embodiment of the grease composition, a grease composition containing component (B2) as the thickener (B) is excluded.

The content of the thickener (B) in the grease composition of this embodiment is preferably 5 mass % or more, more preferably 8 mass % or more, and even more preferably 10 mass % or more, based on the total amount of the grease composition.
The content of the thickener (B) in the grease composition of this embodiment is preferably 30 mass % or less, more preferably 20 mass % or less, and even more preferably 18 mass % or less, based on the total amount of the grease composition.
For example, the content of the thickener (B) in the grease composition of the present embodiment is preferably 5 mass % or more and 30 mass % or less, more preferably 8 mass % or more and 20 mass % or less, and even more preferably 10 mass % or more and 18 mass % or less, relative to the total amount of the grease composition.

When the content of thickener (B) relative to the total amount of the grease composition is within the above preferred range, bearing torque is further reduced.

<Optional ingredients>
The grease composition of this embodiment may contain optional components other than the base oil (A) and thickener (B) described above, such as solid lubricants, anti-wear or extreme pressure agents, antioxidants, oiliness agents, rust inhibitors, and corrosion inhibitors.

Examples of solid lubricants include graphite, graphite fluoride, melamine cyanurate, polytetrafluoroethylene, molybdenum disulfide, antimony sulfide, boron nitride, and alkaline (earth) metal borates. When the grease composition contains a solid lubricant, the content is, for example, 0.1 mass % or more and 20 mass % or less based on the total amount of the grease composition. A single solid lubricant may be used, or multiple solid lubricants may be used in combination.

Examples of anti-wear agents or extreme pressure agents include organic zinc compounds such as zinc dialkyldithiophosphate and zinc dialkyldithiocarbamate; sulfur-containing compounds such as molybdenum dialkyldithiocarbamate, dihydrocarbyl polysulfides, sulfurized esters, thiazole compounds, and thiadiazole compounds; and phosphorus-based extreme pressure agents such as phosphate esters, acid phosphate esters, amine salts of acid phosphate esters, and phosphites. When the grease composition contains an anti-wear agent or extreme pressure agent, the content thereof is, for example, 0.1% by mass or more and 10% by mass or less, based on the total amount of the grease composition. One type of anti-wear agent or extreme pressure agent may be used alone, or multiple anti-wear agents or extreme pressure agents may be used in combination.

Examples of antioxidants include phenolic compounds such as 2,6-di-t-butylphenol and 2,6-di-t-butyl-p-cresol; and amine compounds such as diphenylamine, dialkyldiphenylamine, phenyl-α-naphthylamine, and p-alkylphenyl-α-naphthylamine. When the grease composition contains an antioxidant, the content is, for example, 0.5% by mass or more and 10% by mass or less, based on the total amount of the grease composition. One type of antioxidant may be used alone, or multiple antioxidants may be used in combination.

Examples of oily agents include amines such as laurylamine, myristylamine, palmitylamine, stearylamine, and oleylamine; higher alcohols such as lauryl alcohol, myristyl alcohol, palmityl alcohol, stearyl alcohol, and oleyl alcohol; higher fatty acids such as lauric acid, myristic acid, palmitic acid, stearic acid, and oleic acid; fatty acid esters such as methyl laurate, methyl myristate, methyl palmitate, methyl stearate, and methyl oleate; and fats and oils such as glycerin oleate and glycerin stearate. When the grease composition contains an oily agent, the content thereof is, for example, 0.01% by mass or more and 5% by mass or less, based on the total amount of the grease composition. One oily agent may be used alone, or multiple oily agents may be used in combination.

Examples of rust inhibitors include amines, neutral or overbased petroleum-based or synthetic oil-based metal sulfonates, metal carboxylates, esters, phosphoric acid, and phosphates. When the grease composition contains a rust inhibitor, the content is, for example, 0.005% by mass or more and 5% by mass or less, based on the total amount of the grease composition. A single rust inhibitor may be used, or multiple rust inhibitors may be used in combination.

The corrosion inhibitor may be a known corrosion inhibitor such as a benzotriazole-based compound, a tolyltriazole-based compound, a thiadiazole-based compound, or an imidazole-based compound. When the grease composition contains a corrosion inhibitor, the content thereof is, for example, 0.01% by mass or more and 10% by mass or less, based on the total amount of the grease composition. A single corrosion inhibitor may be used, or multiple corrosion inhibitors may be used in combination.

(Method for producing grease composition)
The method for producing the grease composition of the present embodiment includes a mixing step of mixing the base oil (A) and the thickener (B) to obtain a mixture, and a kneading step of kneading the mixture obtained in the mixing step.

<Mixing process>
The mixing step is a step of mixing the base oil (A) and the thickener (B).
The mixing step can be carried out using, for example, a magnetic stirrer, or by hand.
The mixing step is preferably carried out under heating. The heating temperature is preferably 40°C or higher and 120°C or lower, and more preferably 50°C or higher and 110°C or lower.

<Kneading process>
The kneading step is a step of kneading the mixture obtained in the mixing step.
The kneading step can be carried out using, for example, a three-roll mill, which may be hydraulic or non-hydraulic.
A non-hydraulic three-roll mill is a device that pulverizes, kneads, disperses, and degasses materials by controlling the gap between the rolls and compressing the material by forcing it into the narrow gap between the rolls, and by shearing it due to the difference in roll speed.
On the other hand, a hydraulic three-roll mill (hereinafter also referred to as a "hydraulic roll") is a device that can press rolls together using hydraulic force, and unlike the non-hydraulic three-roll mill described above, it is a device that can more precisely control the load on the material to be kneaded.

When a three-roll mill is used to produce the grease composition, the 1 min/0 min adhesion amount of the grease composition can be controlled by appropriately adjusting the shear force due to the difference in roller speeds and the number of times the material passes through the three-roll mill; when a hydraulic three-roll mill is used, the compression force using the pressure between the rollers, etc.

<Optional process>
The method for producing a grease composition of this embodiment may include optional steps in addition to the mixing step and the kneading step. The optional steps include, before the above-mentioned mixing step, a preparation step of preparing a synthetic material (B0) for synthesizing the thickener (B), a synthesis step of reacting the synthetic material (B0) in the base oil (A) to synthesize the thickener (B), and a cooling step of cooling the mixture obtained in the mixing step.

≪Preparation process≫
The preparation step is a step of preparing a synthesis material (B0) for synthesizing the thickener (B) before the above-mentioned mixing step.
Specific examples of the synthesis material (B0) include carboxylic acids and metal hydroxides with a plurality of different molecular structures for synthesizing the metal complex soap in the component (B1) described above, and diisocyanates and monoamines or diamines for synthesizing the urea compound in the component (B1).

≪Synthesis process≫
The synthesis step is a step of synthesizing a thickener (B) by reacting a synthetic material (B0) in a base oil (A).
The dispersibility of the thickener (B) is improved by synthesizing the thickener (B) by reacting the synthetic material (B0) in the base oil (A) rather than preparing the base oil (A) and the thickener (B) separately and mixing them. In this case, the synthesis step and the mixing step are carried out simultaneously.

The synthesis process is preferably carried out under heating, just like the mixing process. The heating temperature is preferably 40°C or higher and 200°C or lower, and more preferably 50°C or higher and 150°C or lower.

≪Cooling process≫
The cooling step is a step of cooling the mixture obtained in the mixing step.
The mixture may be cooled using a cooler or at room temperature (25° C.).

<Formulation of grease composition>
The grease compositions of Examples 1 and 2 and Comparative Examples 1 to 3 were prepared by blending a base oil (A) and a thickener (B) in the blending ratios shown in Table 1. The values in Table 1 indicate the content (mass%) relative to the total amount of the grease composition.

(1) Base oil (A)
Base oil (A)-1: API Group I base oil (kinematic viscosity at 40°C = 32 mm ² /s)
Base oil (A)-2: Poly-α-olefin (kinematic viscosity at 40° C. = 48 mm ² /s)

(2) Thickener (B)
Thickener (B)-1: Lithium complex soap (lithium complex soap obtained by reaction of lithium hydroxide, 12-hydroxystearic acid, and azelaic acid)
Thickener (B)-2: Lithium stearate soap (single lithium soap)
Thickener (B)-3: Diurea compound (a diurea compound obtained by reacting MDI with octylamine)
Thickener (B)-4: Diurea compound (a diurea compound obtained by reacting MDI with octadecylamine)
Thickener (B)-5: Diurea compound (a diurea compound obtained by reacting MDI with cyclohexylamine)

<Production of grease composition>
(Grease composition of Example 1)
Preparation Step to Cooling Step Base oil (A)-1 was placed in a stainless steel container in the blending ratio shown in Table 1. 12-Hydroxystearic acid was added to the container, heated to 70°C, and stirred with a magnetic stirrer. Next, an aqueous lithium hydroxide solution was added to the container and heated to dehydrate. Thereafter, azelaic acid was added and dissolved at 100°C, lithium hydroxide was added again, and the mixture was heated to dehydrate. By reacting the 12-hydroxystearic acid, azelaic acid, and lithium hydroxide in base oil (A)-1 and synthesizing thickener (B)-1, base oil (A)-1 and thickener (B)-1 were mixed. The mixture was then cooled to room temperature to obtain a semi-solid composition.

Kneading Step The obtained semi-solid composition was kneaded using a three-roll mill to prepare the grease composition of Example 1.

(Grease composition of Example 2)
Preparation Step to Cooling Step Base oil (A)-2 was divided into two stainless steel containers so that the total amount was the blending ratio shown in Table 1.
MDI was added to one stainless steel container, heated to 60 to 65°C, and stirred with a magnetic stirrer to obtain a mixed solution P. Octylamine was added to the other stainless steel container, heated to 60 to 65°C, and stirred with a magnetic stirrer to obtain a mixed solution Q. Next, mixed solutions P and Q were mixed and stirred with a magnetic stirrer at 60 to 65°C, whereby MDI and octylamine were reacted in base oil (A)-2, synthesizing thickener (B)-3, while base oil (A)-1 and thickener (B)-3 were mixed. The mixture was then cooled to room temperature to obtain a semi-solid composition.

Kneading Step The obtained semi-solid composition was kneaded using a three-roll mill to prepare the grease composition of Example 2.

(Grease composition of Comparative Example 1)
Preparation Step to Cooling Step Base oil (A)-1 was placed in a stainless steel container in the blending ratio shown in Table 1. Stearic acid was added to the container, heated to 70°C, and an aqueous lithium hydroxide solution was added while stirring with a magnetic stirrer. The mixture was then heated and dehydrated, causing the stearic acid and lithium hydroxide to react in base oil (A)-1, synthesizing thickener (B)-2, while mixing base oil (A)-1 and thickener (B)-2. The mixture was then cooled to room temperature, yielding a semi-solid composition.

Kneading Step The obtained semi-solid composition was kneaded using a three-roll mill to prepare the grease composition of Comparative Example 1.

(Grease composition of Comparative Example 2)
A grease composition of Comparative Example 2 was prepared in the same manner as in Example 2, except that the amine used as a raw material was changed from octylamine to octadecylamine.

(Grease composition of Comparative Example 3)
A grease composition of Comparative Example 3 was prepared in the same manner as in Example 2, except that the amine used as a raw material was changed from octylamine to cyclohexylamine.

[Evaluation of consistency]
The worked penetration of each grease composition measured in accordance with JIS K2220:2013 is shown in Table 1.

[Evaluation of adhesion amount to bearing balls]
The 0-minute adhesion amount, 1-minute adhesion amount, and 60-minute adhesion amount of the grease composition of each example were calculated by the following method.
(i) 0.25 g (2 g in total) of the grease composition of each example was filled onto the cage at eight locations between the bearing balls of a 6204 ball bearing, and each was sealed with a rubber seal to create a sample of each example.
(ii) The sample was fixed on a rotating stage and irradiated with a neutron beam using the RADEN described above. The neutrons that passed through the sample were converted into visible light using a 0.10 mm thick ⁶ LiF/ZnS scintillator screen, and then the transmission image was saved using a water-cooled CCD camera with 2048 x 2048 pixels. For radiographic observation, neutrons were irradiated in the axial direction of the 6204 ball bearing with a field of view of 80 mm x 80 mm and a camera exposure time of approximately 30 seconds. The spatial resolution of the obtained transmission image was 60 μm.
(iii) A three-dimensional image was generated using filtered back projection from 600 transmission images obtained by rotating the sample from 0° to 360° in 0.6° increments.
(iv) In the three-dimensional images obtained in (iii), the volume ( ^μm3 ) of the grease composition portion of each example was calculated by image analysis, with a measurement range 1.2 times the diameter of the bearing ball. The amount of adhesion at 0 min was calculated from the average volume of the grease composition of each example adhered to the eight bearing balls (average of six values excluding the minimum and maximum values).
(v) The ball bearing was rotated at 2000 rpm for 1 minute under atmospheric pressure at 25°C, and then the steps (ii) to (iv) were carried out to calculate the 1-minute adhesion amount. The ball bearing was also rotated at 2000 rpm for 60 minutes under atmospheric pressure at 25°C, and then the steps (ii) to (iv) were carried out to calculate the 60-minute adhesion amount.
The average of the 0-minute adhesion weight, 1-minute adhesion weight, and 60-minute adhesion weight, as well as the average (average value of six values) excluding the maximum and minimum values of each adhesion weight, are shown in Table 2. Table 2 also shows the 1-minute adhesion weight/0-minute adhesion weight and the 60-minute adhesion weight/1-minute adhesion weight.
4 to 13 show a portion of the image analysis data used to measure the amount of adhesion of the grease composition of each example.

FIG. 4 shows image analysis data used to measure the amount of the grease composition of Example 1 attached to the bearing balls before the start of rotation.
FIG. 5 shows image analysis data used to measure the amount of the grease composition of Example 1 adhering to the bearing balls 60 minutes after the start of rotation.
FIG. 6 shows image analysis data used to measure the amount of the grease composition of Comparative Example 1 adhering to the bearing balls before the start of rotation.
FIG. 7 shows image analysis data used to measure the amount of the grease composition of Comparative Example 1 adhering to the bearing balls 60 minutes after the start of rotation.
FIG. 8 shows image analysis data used to measure the amount of the grease composition of Example 2 adhering to the bearing balls before the start of rotation.
FIG. 9 shows image analysis data used to measure the amount of the grease composition of Example 2 adhering to the bearing balls 60 minutes after the start of rotation.
FIG. 10 shows image analysis data used to measure the amount of the grease composition of Comparative Example 2 adhering to the bearing balls before the start of rotation.
FIG. 11 shows image analysis data used to measure the amount of the grease composition of Comparative Example 2 adhering to the bearing balls 60 minutes after the start of rotation.
FIG. 12 shows image analysis data used to measure the amount of the grease composition of Comparative Example 3 adhering to the bearing balls before the start of rotation.
FIG. 13 shows image analysis data used to measure the amount of the grease composition of Comparative Example 3 adhering to the bearing balls 60 minutes after the start of rotation.

[Bearing torque evaluation]
A bearing sample was prepared using the method described in (i), and an axial load of 50 N and a radial load of 50 N were applied. The inner ring was rotated at 2000 rpm at room temperature, and the tangential force acting on the housing was measured with a load cell to calculate the bearing torque (mN m). The bearing torque was measured 30 minutes after the start of rotation. The bearing torque results for each example grease composition are shown in Table 2.

As shown in Table 2, the grease composition of Example 1, in which the 1 min adhesion amount/0 min adhesion amount was 129%, and the grease composition of Example 2, in which the 1 min adhesion amount/0 min adhesion amount was 94%, had lower bearing torque and better torque performance than the grease compositions of Comparative Examples 1 to 3. This demonstrates that grease compositions in which the amount of adhesion to the bearing balls does not change significantly even when the ball bearing is rotating will have excellent torque performance.

Claims (4)

A method for producing a grease composition containing a base oil (A) and a thickener (B), comprising :
The grease composition is such that, when 2 g of the grease composition is filled into a 6204 ball bearing, the ball bearing is rotated at a speed of 2000 rpm under atmospheric pressure at 25°C for a predetermined time, and the amount of the grease composition adhering to the bearing balls in the ball bearing is measured using neutron observation, the ratio of the amount of the grease composition adhering to the bearing balls one minute after the start of rotation to the amount of the grease composition adhering to the bearing balls before the start of rotation is 70% or more and 140% or less,
a preparation step of preparing a synthesis material (B0) for synthesizing the thickener (B);
a synthesis step of synthesizing the thickener (B) by reacting the synthesis material (B0) in the base oil (A);
a mixing step of mixing the synthesized thickener (B) with the base oil (A);
a kneading step of kneading the mixture obtained in the mixing step,
In the kneading step, a three-roll mill is used,
A method for producing a grease composition, wherein one or more selected from the group consisting of a shear force due to a speed difference between rollers of the three-roll mill, a number of times the material is passed through the three-roll mill, and a compressive force utilizing pressure between the rollers are adjusted to control the ratio of the amount of the grease composition adhering to the bearing balls to 70% or more and 140% or less . 2. The method for producing a grease composition according to claim 1, wherein the thickener (B) comprises one or more thickeners (B1) selected from metal complex soaps and urea compounds. The method for producing a grease composition according to claim 2, wherein the urea compound is a diurea compound obtained by reacting diphenylmethane-4,4'-diisocyanate (MDI) with octylamine. The content of the base oil (A) is 50% by mass or more and 95% by mass or less based on the total amount of the grease composition,
3. The method for producing a grease composition according to claim 1, wherein the content of the thickener (B) is 5% by mass or more and 30% by mass or less based on the total amount of the grease composition.