Patent Description:
This application claims priority based on the <CIT>.

Grease compositions are used to lubricate sliding parts such as rolling bearings, gears, and so forth. Patent Documents <NUM> to <NUM> describe grease compositions.

Grease compositions used for lubrication of rolling bearings, gears, and so forth, are required to have good oil retention properties in order to ensure good lubrication. Also, in order to meet needs for energy conservation and high efficiency of rolling bearings, gears, and so forth, the above-mentioned grease compositions are required to be capable of reducing torque. That is to say, there is demand for a grease composition that has good oil retention properties and can also ensure low torque properties when used with rolling bearings, gears, and the like.

A grease composition according to one aspect of the present disclosure includes a base oil and a thickener. (not part of the invention).

The thickener contains a urea compound and a styrene-based polymer, in which a content of the styrene-based polymer is <NUM>% by mass or more and <NUM>% by mass or less as to a total amount of the urea compound and the styrene-based polymer. Particles of the thickener that have diameters of <NUM> or more have an average value of diameter of <NUM> or more and <NUM> or less.

A production method of a grease composition according to another aspect of the present disclosure includes providing a styrene-based polymer, an amine compound, an isocyanate compound, a lubricating oil, a first solvent that does not dissolve a urea compound that is generated, and a second solvent that does not dissolve the urea compound that is generated, dissolving or dispersing the amine compound in the first solvent, dissolving or dispersing the isocyanate compound in the second solvent, dissolving or dispersing the styrene-based polymer in one or both of the first solvent and the second solvent, such that a first blended solution containing at least the amine compound and a second blended solution containing at least the isocyanate compound are prepared, blending the first blended solution and the second blended solution, and carrying out reaction of the amine compound and the isocyanate compound, such that a third blended solution containing the styrene-based polymer and the urea compound is generated, and adding the lubricating oil after removing the first solvent and the second solvent from the third blended solution.

A production method of a grease composition according to another aspect of the present disclosure includes providing a styrene-based polymer, an amine compound, an isocyanate compound, a first lubricating oil, and a second lubricating oil, dissolving or dispersing the amine compound in the first lubricating oil, dissolving or dispersing the isocyanate compound in the second lubricating oil, dissolving or dispersing the styrene-based polymer in one or both of the first lubricating oil and the second lubricating oil, such that a fourth blended solution containing at least the amine compound and a fifth blended solution containing at least the isocyanate compound are prepared, and blending the fourth blended solution and the fifth blended solution, and carrying out reaction of the amine compound and the isocyanate compound.

The grease composition according to the present disclosure has excellent oil retention properties. The grease composition according to the present disclosure can ensure low torque properties when used with rolling bearings, gears, and the like. According to the production method of the grease composition according to the present disclosure, the grease composition of the present disclosure can be suitably produced.

<Overview of Embodiments of Invention According to Present Disclosure> Hereinafter, an outline of the embodiments of the invention of the present disclosure will be listed and described.

The above grease composition contains a urea compound and a predetermined amount of a styrene-based polymer as a thickener, and the particles of the thickener that have diameters of <NUM> or more have an average value of diameter of <NUM> or more and <NUM> or less. That is to say, the grease composition does not contain coarse thickener particles that tend to occur when the urea compound alone is contained therein. Accordingly, the above grease composition retains oil well. In other words, the above grease composition has good oil retention properties. Further, the above grease composition enables rolling bearings, gears, and so forth, to operate with low torque. In other words, the above grease composition has good low torque properties.

On the other hand, the above-mentioned Patent Documents <NUM> to <NUM> do not describe that both good oil retention properties and good low torque properties can be achieved through a thickener that contains a urea compound and a predetermined amount of a styrene-based polymer, in which the particles that have diameters of <NUM> or more have an average value of diameter of <NUM> or more and <NUM> or less.

(<NUM>) In the grease composition according to (<NUM>) above, the content of the styrene-based polymer may be <NUM>% by mass or more and <NUM>% by mass or less as to the total amount of the urea compound and the styrene-based polymer.

(<NUM>) In the grease composition according to (<NUM>) or (<NUM>) above, the urea compound is preferably diurea. In this case, even when the grease composition is used at high temperatures, the grease composition does not readily deteriorate. In other words, the above grease composition has good heat resistance.

(<NUM>) In the grease composition according to any one of (<NUM>) to (<NUM>) above, the base oil is preferably poly-α-olefin. In this case, the grease composition has excellent fluidity at low temperatures. In other words, the above grease composition has good low-temperature fluidity. Further, members such as members made of rubber or resin around rolling and sliding faces that require lubrication, such as rolling bearings, gears, and so forth, for example, are less likely to deteriorate. In other words, the grease composition exhibits little aggression with respect to members made of rubber or made of resin.

(<NUM>) In the grease composition according to any one of (<NUM>) to (<NUM>) above, a content of the thickener is preferably <NUM>% by mass or more and <NUM>% by mass or less as to a total amount of the base oil and the thickener. In this case, the grease composition has even better low torque properties.

(<NUM>) In a production method of a grease composition according to an embodiment of the present disclosure, a styrene-based polymer, an amine compound, an isocyanate compound, a lubricating oil, a first solvent that does not dissolve a urea compound that is generated, and a second solvent that does not dissolve the urea compound that is generated, are provided, the amine compound and the styrene-based polymer are dissolved or dispersed in the first solvent, thereby preparing a first blended solution, the isocyanate compound and the styrene-based polymer are dissolved or dispersed in the second solvent, thereby preparing a second blended solution, the first blended solution and the second blended solution are blended and reaction of the amine compound and the isocyanate compound is carried out, such that a third blended solution containing the styrene-based polymer and the urea compound is generated, and the lubricating oil is added after removing the first solvent and the second solvent from the third blended solution.

(<NUM>) In a production method of a grease composition according to another embodiment of the present disclosure, a styrene-based polymer, an amine compound, an isocyanate compound, a lubricating oil, a first solvent that does not dissolve a urea compound that is generated, and a second solvent that does not dissolve the urea compound that is generated, are provided, the amine compound is dissolved or dispersed in the first solvent, thereby preparing a first blended solution, the isocyanate compound and the styrene-based polymer are dissolved or dispersed in the second solvent, thereby preparing a second blended solution, the first blended solution and the second blended solution are blended and reaction of the amine compound and the isocyanate compound is carried out, such that a third blended solution containing the styrene-based polymer and the urea compound is generated, and the lubricating oil is added after removing the first solvent and the second solvent from the third blended solution.

(<NUM>) In a production method of a grease composition according to another embodiment of the present disclosure, a styrene-based polymer, an amine compound, an isocyanate compound, a lubricating oil, a first solvent that does not dissolve a urea compound that is generated, and a second solvent that does not dissolve the urea compound that is generated, are provided, the amine compound and the styrene-based polymer are dissolved or dispersed in the first solvent, thereby preparing a first blended solution, the isocyanate compound is dissolved or dispersed in the second solvent, thereby preparing a second blended solution, the first blended solution and the second blended solution are blended and reaction of the amine compound and the isocyanate compound is carried out, such that a third blended solution containing the styrene-based polymer and the urea compound is generated, and the lubricating oil is added after removing the first solvent and the second solvent from the third blended solution.

(<NUM>) In a production method of a grease composition according to another embodiment of the present disclosure, a styrene-based polymer, an amine compound, an isocyanate compound, a first lubricating oil, and a second lubricating oil are provided, the amine compound and the styrene-based polymer are dissolved or dispersed in the first lubricating oil, thereby preparing a fourth blended solution, the isocyanate compound and the styrene-based polymer are dissolved or dispersed in the second lubricating oil, thereby preparing a fifth blended solution, the fourth blended solution and the fifth blended solution are blended, and reaction of the amine compound and the isocyanate compound is carried out.

(<NUM>) In a production method of a grease composition according to another embodiment of the present disclosure, a styrene-based polymer, an amine compound, an isocyanate compound, a first lubricating oil, and a second lubricating oil are provided, the amine compound is dissolved or dispersed in the first lubricating oil, thereby preparing a fourth blended solution, the isocyanate compound and the styrene-based polymer are dissolved or dispersed in the second lubricating oil, thereby preparing a fifth blended solution, the fourth blended solution and the fifth blended solution are blended, and reaction of the amine compound and the isocyanate compound is carried out.

(<NUM>) In a production method of a grease composition according to another embodiment of the present disclosure, a styrene-based polymer, an amine compound, an isocyanate compound, a first lubricating oil, and a second lubricating oil are provided, the amine compound and the styrene-based polymer are dissolved or dispersed in the first lubricating oil, thereby preparing a fourth blended solution, the isocyanate compound is dissolved or dispersed in the second lubricating oil, thereby preparing a fifth blended solution, the fourth blended solution and the fifth blended solution are blended, and reaction of the amine compound and the isocyanate compound is carried out.

According to these production methods of (<NUM>) to (<NUM>), the grease composition according to the embodiment of the present disclosure can be suitably produced.

Embodiments of the invention according to the present disclosure will be described below. Note that in the present disclosure, the embodiments of the invention should be understood to be exemplary in all respects and not restrictive. The scope of rights of the present invention is set forth in the claims, and is intended to include all modifications that fall within the meaning and scope equivalent to the claims.

First, a device and the like in which the grease composition according to the present disclosure is used will be described, following which embodiments regarding the grease composition according to the present disclosure will be described. The grease composition according to the present disclosure is used in, for example, dual-pinion type electric power steering systems, column type electric power steering systems, rolling bearings, and so forth.

<FIG> is a configuration diagram schematically illustrating an example of a dual-pinion type electric power steering system <NUM> including a steering gear device <NUM>.

<FIG> is a sectional view taken along A-A in <FIG>, illustrating a portion of the steering gear device <NUM>. In <FIG>, a lower side of the drawing corresponds to a lower side in a vertical direction when installed in a vehicle.

<FIG> is a sectional view taken along B-B in <FIG>, illustrating a portion of the steering gear device <NUM>. In <FIG>, the lower side of the drawing corresponds to the lower side in the vertical direction when installed in the vehicle.

The dual-pinion type electric power steering system <NUM> includes a steering wheel <NUM>, a steering shaft <NUM>, a first pinion shaft <NUM>, a rack shaft <NUM>, a housing <NUM>, two rack bushings <NUM> and <NUM>, two bearings <NUM> and <NUM>, a first rack guide mechanism <NUM>, and a steering assistance device <NUM>. The steering assistance device <NUM> includes a controller <NUM>, a torque sensor <NUM>, an electric motor <NUM>, a speed reducing mechanism <NUM>, a second pinion shaft <NUM>, two bearings <NUM> and <NUM>, a worm housing <NUM>, and a second rack guide mechanism <NUM>. The speed reducing mechanism <NUM> includes a worm <NUM> and a worm wheel <NUM>.

A driver who drives an automobile equipped with this dual-pinion type electric power steering system <NUM> performs steering operations by turning the steering wheel <NUM>. The steering shaft <NUM> includes a column shaft <NUM>, a first universal joint <NUM>, an intermediate shaft <NUM>, and a second universal joint <NUM>. The first universal joint <NUM> includes a first yoke that is omitted from illustration, a plurality of first rolling elements that is omitted from illustration, a first joint spider that is omitted from illustration, a plurality of second rolling elements that is omitted from illustration, and a second yoke that is omitted from illustration. The second universal joint <NUM> includes a third yoke that is omitted from illustration, a plurality of third rolling elements that is omitted from illustration, a second joint spider that is omitted from illustration, a plurality of fourth rolling elements that is omitted from illustration, and a fourth yoke that is omitted from illustration.

The column shaft <NUM> fixes the steering wheel <NUM> at one end thereof in an extending direction. The column shaft <NUM> fixes the first yoke of the first universal joint <NUM> at the other end thereof in the extending direction. The column shaft <NUM> is rotatable about a central axis in the extending direction. The first yoke is pivotably fitted to a first pair of trunnions located on the same central axis of the first joint spider via the plurality of first rolling elements. The second yoke is pivotably fitted to a second pair of trunnions located on the same central axis of the first joint spider via the plurality of second rolling elements. The central axes of the first pair of trunnions and the central axes of the second trunnions intersect at an angle of <NUM> degrees.

The second yoke of the first universal joint <NUM> fixes one end of the intermediate shaft <NUM> in the extending direction thereof. The intermediate shaft <NUM> fixes the third yoke of the second universal joint <NUM> at the other end thereof in the extending direction. The third yoke is pivotably fitted to a third pair of trunnions located on the same central axis of the second joint spider via the plurality of third rolling elements. The fourth yoke is pivotably fitted to a fourth pair of trunnions located on the same central axis of the second joint spider via the plurality of fourth rolling elements. The central axes of the third pair of trunnions and the central axes of the fourth trunnions intersect at an angle of <NUM> degrees. The fourth yoke of the second universal joint <NUM> fixes one end of the first pinion shaft <NUM> in the extending direction thereof. Thus, when the driver turns the steering wheel <NUM>, the column shaft <NUM> turns about the central axis thereof in the extending direction thereof, the intermediate shaft <NUM> also turns about a central axis thereof in the extending direction thereof, and the first pinion shaft <NUM> also turns about a central axis thereof in the extending direction thereof.

In the dual-pinion type electric power steering system <NUM>, the first pinion shaft <NUM>, the rack shaft <NUM>, the housing <NUM>, the two rack bushings <NUM> and <NUM>, a first bearing <NUM>, a second bearing <NUM>, the first rack guide mechanism <NUM>, the electric motor <NUM>, the speed reducing mechanism <NUM>, the second pinion shaft <NUM>, a third bearing <NUM>, a fourth bearing <NUM>, the worm housing <NUM>, and the second rack guide mechanism <NUM> make up the steering gear device <NUM> that serves as a rack and pinion type steering device. In <FIG>, the housing <NUM> is represented by a hidden outline (long dashed double-short dashed lines), and inside thereof is illustrated.

The first pinion shaft <NUM> extends from an upper side toward the lower side of the automobile in the vertical direction. The first pinion shaft <NUM> includes, from one end side toward the other end in the extending direction thereof, a serrated portion <NUM>, a first shaft portion <NUM>, a first pinion toothed portion <NUM>, and a first boss portion <NUM>. Serrations are formed in the serrated portion <NUM>. The fourth yoke of the second universal joint <NUM> is fixed to the serrations of the serrated portion <NUM>. The first shaft portion <NUM> has a cylindrical shape. First pinion teeth <NUM> are formed over the entire face of the first pinion toothed portion <NUM> in the circumferential direction. An extending direction of the first pinion teeth <NUM> has an angle that is not <NUM> degrees with respect to the extending direction of the central axis of the first pinion shaft <NUM>. The first boss portion <NUM> has a cylindrical shape.

The housing <NUM> has a first opening <NUM> on a steering wheel <NUM> side thereof, and a side opposite to the first opening <NUM> is sealed off. The first pinion shaft <NUM> is accommodated within the housing <NUM>. The first pinion shaft <NUM> is rotatably supported by the two bearings <NUM> and <NUM>, with respect to the housing <NUM>. The first bearing <NUM> is a ball bearing. The first bearing <NUM> includes an inner ring, an outer ring, and balls, with the inner ring being fixed to the first shaft portion <NUM> and also the outer ring being fixed to the housing <NUM>, and the balls roll between the inner ring and the outer ring. The second bearing <NUM> is a roller bearing. The second bearing <NUM> includes rollers and an outer ring, with the outer ring being fixed to the housing <NUM>, and the rollers roll on an outer peripheral face of the first boss portion <NUM> and the outer ring.

A lid <NUM>, through which the first pinion shaft <NUM> passes in a state in which the first pinion shaft <NUM>, the first bearing <NUM>, and the second bearing <NUM> are inserted into the housing <NUM>, is fixed to the first opening <NUM> of the housing. A seal is fixed to the lid <NUM>, and the seal is slidable on an outer peripheral face 322b of the first shaft portion <NUM> of the first pinion shaft <NUM>. A cover member <NUM> is further fixed to the housing <NUM>. The cover member <NUM> covers a portion of the first shaft portion <NUM> of the first pinion shaft <NUM> from the outside, in a radial direction.

The rack shaft <NUM> is provided with, from one end to the other end in an extending direction thereof, a first cylindrical portion <NUM>, a first rack toothed portion <NUM>, a second cylindrical portion <NUM>, a second rack toothed portion <NUM>, and a third cylindrical portion <NUM>. The first rack toothed portion <NUM> has first rack teeth <NUM> formed on a portion thereof in the circumferential direction, and the other portion thereof in the circumferential direction is a cylindrical face <NUM> of which a central axis is the extending direction of the rack shaft <NUM>. The second rack toothed portion <NUM> has second rack teeth <NUM> formed on a portion thereof in the circumferential direction, and the other portion thereof in the circumferential direction is a cylindrical face <NUM> of which a central axis is the extending direction of the rack shaft <NUM>. An outer peripheral face of the first cylindrical portion <NUM>, an outer peripheral face of the second cylindrical portion <NUM>, and an outer peripheral face of the third cylindrical portion <NUM> are each a cylindrical face of which the central axis is in the extending direction of the rack shaft <NUM>. The extending direction of the first rack teeth <NUM> has an angle that is not <NUM> degrees with respect to the extending direction of the rack shaft. The extending direction of the second rack teeth <NUM> has an angle that is not <NUM> degrees with respect to the extending direction of the rack shaft <NUM>. With the angle of the first rack teeth <NUM> with respect to the extending direction of the rack shaft <NUM> as X, the angle of the second rack teeth <NUM> with respect to the extending direction of the rack shaft <NUM> is π-X.

The housing <NUM> extends in a direction different from the first opening <NUM> on the steering wheel <NUM> side, and has a second opening <NUM> at one end in the extending direction and a third opening <NUM> at the other end thereof. The rack shaft <NUM> is accommodated within the housing <NUM>, along the direction in which the housing <NUM> extends. The first cylindrical portion <NUM> that is at one end of the rack shaft <NUM> in the extending direction thereof protrudes from the second opening <NUM> at one end of the housing <NUM> in the extending direction thereof. The third cylindrical portion <NUM> at the other end of the rack shaft <NUM> in the extending direction thereof protrudes from the third opening <NUM> at the other end of the housing <NUM> in the extending direction thereof. The housing <NUM> has a fourth opening <NUM>. The fourth opening <NUM> is located closer to the other end side in the extending direction of the housing than the first opening <NUM> is. The housing <NUM> further has a fifth opening <NUM> and a sixth opening <NUM>. The fifth opening <NUM> is located at approximately the same position in the extending direction of the housing <NUM> as the first opening <NUM>, in a direction perpendicular to the first opening <NUM>, in a radial direction with the extending direction of the housing <NUM> as the central axis. The sixth opening <NUM> is located at approximately the same position in the extending direction of the housing <NUM> as the fourth opening <NUM>, in a direction perpendicular to the fourth opening <NUM>, in a radial direction with the extending direction of the housing <NUM> as the central axis.

A first rack bushing <NUM> is fixed to one end of the housing <NUM> in the extending direction. The first rack bushing <NUM> is fixed to the housing <NUM>, adjacent to the second opening <NUM>. The first rack bushing <NUM> is slidable on the outer peripheral face of the first cylindrical portion <NUM> of the rack shaft <NUM>. A second rack bushing <NUM> is fixed to the other end of the housing <NUM> in the extending direction. The second rack bushing <NUM> is fixed to the housing <NUM>, adjacent to the third opening <NUM>. The second rack bushing <NUM> is slidable on the outer peripheral face of the third cylindrical portion <NUM> of the rack shaft <NUM>.

The first pinion teeth <NUM> formed on the first pinion toothed portion <NUM> of the first pinion shaft <NUM>, and the first rack teeth <NUM> formed on the first rack toothed portion <NUM> of the rack shaft <NUM> are capable of rolling-sliding contact via the grease composition G. The first pinion teeth <NUM> and the first rack teeth <NUM> are meshed with each other via the grease composition G. When the first pinion shaft <NUM> turns relative to the housing <NUM> about the central axis in the extending direction thereof, the rack shaft <NUM> moves in a linear direction relative to the housing <NUM> in the extending direction of the housing <NUM>.

The first rack guide mechanism <NUM> is fixed to the housing <NUM>. The first rack guide mechanism <NUM> is fixed to the fifth opening <NUM>. The fifth opening <NUM> is at the cylindrical face <NUM> side that is the other portion of the first rack toothed portion <NUM> of the rack shaft <NUM> in the circumferential direction, at a position where the first pinion shaft <NUM> meshes with the rack shaft <NUM>, in the extending direction of the housing <NUM>.

The first rack guide mechanism <NUM> includes a first support yoke <NUM>, a first sheet member <NUM>, a first coil spring <NUM>, and a first plug <NUM>. The first sheet member <NUM> is interposed between the cylindrical face <NUM>, which is the other portion of the first rack toothed portion <NUM> of the rack shaft <NUM> in the circumferential direction, and the cylindrical face of the first support yoke <NUM>. The first sheet member <NUM> is fixed to the first support yoke <NUM>. The first sheet member <NUM> and the cylindrical face <NUM>, which is the other portion of the first rack toothed portion <NUM> of the rack shaft <NUM> in the circumferential direction, are capable of sliding contact via the grease composition G. The first plug <NUM> is fixed to the fifth opening <NUM> of the housing <NUM>. The first plug <NUM> is in contact with one end of the first coil spring <NUM>. The first support yoke <NUM> is in contact with the other end of the first coil spring <NUM>. The first coil spring <NUM> is shorter than a free length thereof in a state in which the first plug <NUM> is fixed to the fifth opening <NUM>. Thus, the first sheet member <NUM> is pressed against the rack shaft <NUM> with respect to the housing <NUM>.

The second pinion shaft <NUM> extends from the upper side to the lower side of the automobile in the vertical direction. The second pinion shaft <NUM> includes, from one end side to the other end along the extending direction thereof, a fitting portion <NUM>, a second shaft portion <NUM>, a second pinion toothed portion <NUM>, and a second boss portion <NUM>. The fitting portion <NUM> has a cylindrical shape. The second shaft portion <NUM> has a cylindrical shape. Second pinion teeth <NUM> are formed over the entire face of the second pinion toothed portion <NUM> in the circumferential direction. An extending direction of the second pinion teeth <NUM> has an angle that is not <NUM> degrees with respect to the extending direction of the central axis of the second pinion shaft <NUM>. The second boss portion <NUM> has a cylindrical shape.

The worm wheel <NUM> is fitted into the fitting portion <NUM>. The worm <NUM> is fixed to an output shaft <NUM> of the electric motor <NUM>. The electric motor <NUM> is fixed to the worm housing <NUM>. The worm housing <NUM> has a seventh opening <NUM>. The output shaft <NUM> of the electric motor <NUM> is disposed in internal space of the worm housing <NUM> via the seventh opening <NUM>. The electric motor <NUM> is fixed to the worm housing <NUM> so as to close off the seventh opening <NUM> of the worm housing <NUM>.

The worm <NUM> is disposed in internal space of the worm housing <NUM>. The worm wheel <NUM> is disposed in the internal space of the worm housing <NUM>. The worm housing <NUM> has an eighth opening <NUM> vertically upward, and an assembly of the second pinion shaft <NUM> and the worm wheel <NUM> is inserted into the internal space of the worm housing <NUM> from the eighth opening <NUM>. The eighth opening is closed with a lid <NUM>. The worm housing <NUM> has a ninth opening <NUM> on the opposite side from the eighth opening <NUM>. A portion of the second shaft portion <NUM> of the second pinion shaft <NUM>, the second pinion toothed portion <NUM>, and the second boss portion <NUM> protrude from the ninth opening <NUM> of the worm housing <NUM>.

The worm housing <NUM> is fixed to the housing <NUM>. The ninth opening <NUM> of the worm housing <NUM> and the fourth opening <NUM> of the housing <NUM> communicate with each other to seal off the internal space from the external space.

The third bearing <NUM> is a ball bearing. The bearing <NUM> includes an inner ring, an outer ring, and balls, with the inner ring being fixed to the second shaft portion <NUM> and also the outer ring being fixed to the worm housing <NUM>, and the balls roll between the inner ring and the outer ring. The bearing <NUM> is a roller bearing. The bearing <NUM> includes rollers and an outer ring, with the outer ring being fixed to the housing <NUM>, and the rollers roll on an outer peripheral face of the second boss portion <NUM> and the outer ring.

The second pinion teeth <NUM> formed on the second pinion toothed portion <NUM> of the second pinion shaft <NUM>, and the second rack teeth <NUM> formed on the second rack toothed portion <NUM> of the rack shaft <NUM> are capable of rolling-sliding contact via the grease composition G. The second pinion teeth <NUM> and the second rack teeth <NUM> are meshed with each other via the grease composition G. When the second pinion shaft <NUM> turns relative to the housing <NUM> about the central axis in the extending direction thereof, the rack shaft <NUM> moves in the linear direction relative to the housing <NUM> in the extending direction of the housing <NUM>.

The second rack guide mechanism <NUM> is fixed to the housing <NUM>. The second rack guide mechanism <NUM> is fixed to the sixth opening <NUM>. The sixth opening <NUM> is at the cylindrical face <NUM> side that is the other portion of the second rack toothed portion <NUM> of the rack shaft <NUM> in the circumferential direction, at a position where the second pinion shaft <NUM> meshes with the rack shaft <NUM>, in the extending direction of the housing <NUM>.

The second rack guide mechanism <NUM> includes a second support yoke <NUM>, a second sheet member <NUM>, a second coil spring <NUM>, and a second plug <NUM>. The second sheet member <NUM> is interposed between the cylindrical face <NUM>, which is the other portion of the second rack toothed portion <NUM> of the rack shaft <NUM> in the circumferential direction, and a cylindrical face of the second support yoke <NUM>. The second sheet member <NUM> is fixed to the second support yoke <NUM>. The second sheet member <NUM> and the cylindrical face <NUM>, which is the other portion of the second rack toothed portion <NUM> of the rack shaft <NUM> in the circumferential direction, are capable of sliding contact via the grease composition G. The second plug <NUM> is fixed to the sixth opening <NUM> of the housing <NUM>. The second plug <NUM> is in contact with one end of the second coil spring <NUM>. The second support yoke <NUM> is in contact with the other end of the second coil spring <NUM>. The second coil spring <NUM> is shorter than a free length thereof in a state in which the second plug <NUM> is fixed to the sixth opening <NUM>. Thus, the second sheet member <NUM> is pressed against the rack shaft <NUM> with respect to the housing <NUM>.

The torque sensor <NUM> detects steering torque applied by the driver to the steering wheel <NUM> through the column shaft <NUM>. The speed reducing mechanism <NUM> is an assembly in which the worm <NUM> that rotates integrally with the output shaft <NUM> of the electric motor <NUM> and the worm wheel <NUM> that rotates integrally with the second pinion shaft <NUM> mesh with each other. A motor current is supplied to the electric motor <NUM> from the controller <NUM>. The controller <NUM> controls the electric motor <NUM> based on the steering torque detected by the torque sensor <NUM>, vehicle speed, and so forth, and transmits rotational force of the output shaft <NUM> of the electric motor <NUM>, of which speed is reduced by the speed reducing mechanism <NUM>, to the second pinion shaft <NUM>. The rotational force of the second pinion shaft <NUM> is applied from the second pinion teeth <NUM> to the second rack teeth <NUM>, as a steering assisting force.

The housing <NUM> is fixed to an automobile that is omitted from illustration, with the extending direction of the housing <NUM> aligned with a vehicle-width direction. Ball joint sockets <NUM>, <NUM> are fixed to one end and the other end of the rack shaft <NUM>, respectively, and tie rods <NUM>, <NUM> connected to these ball joint sockets <NUM>, <NUM>, respectively, are connected to bearing rings of rolling bearings that rotatably support a right and left pair of front wheels <NUM>, <NUM> via knuckle arms <NUM>, <NUM>. Moving the rack shaft <NUM> in the linear direction, in the extending direction of the housing <NUM>, steers the right and left front wheels <NUM>, <NUM>, which are steered wheels.

The grease composition G is sealed within the housing <NUM>. The grease composition G is interposed between rolling and sliding faces of the first pinion teeth <NUM> and rolling and sliding faces of the first rack teeth <NUM>, which are in contact with each other when the first pinion teeth <NUM> and the first rack teeth <NUM> mesh with each other, thereby lubricating between the rolling and sliding faces of both. The grease composition G is interposed between a sliding face of the first sheet member <NUM> and a sliding face of the cylindrical face <NUM>, which is the other portion of the first rack toothed portion <NUM> of the rack shaft <NUM> in the circumferential direction, where the first sheet member <NUM> and the rack shaft <NUM> come into contact by being pressed against each other, thereby lubricating between both sliding faces. The grease composition G is interposed between rolling and sliding faces of the second pinion teeth <NUM> and rolling and sliding faces of the second rack teeth <NUM>, which are in contact with each other when the second pinion teeth <NUM> and the second rack teeth <NUM> mesh with each other, thereby lubricating between the rolling and sliding faces of both. The grease composition G is interposed between a sliding face of the second sheet member <NUM> and a sliding face of the cylindrical face <NUM>, which is the other portion of the second rack toothed portion <NUM> of the rack shaft <NUM> in the circumferential direction, where the second sheet member <NUM> and the rack shaft <NUM> come into contact by being pressed against each other, thereby lubricating between both sliding faces.

The steering gear device <NUM> configured in this way has the grease composition according to the present disclosure sealed therein, as the grease composition G. The grease composition according to the present disclosure ensures oil retention properties, and accordingly the steering gear device <NUM> has good seizure resistance and wear resistance.

<FIG> is a configuration diagram schematically illustrating an example of a column type electric power steering system <NUM> including a steering gear device <NUM>.

<FIG> is a sectional view taken along A-A in <FIG>, illustrating a portion of the steering gear device <NUM>. In <FIG>, the lower side of the drawing corresponds to the lower side in the vertical direction when installed in a vehicle.

The column type electric power steering system <NUM> includes a steering wheel <NUM>, a steering shaft <NUM>, a pinion shaft <NUM>, a rack shaft <NUM>, a housing <NUM>, two rack bushings <NUM> and <NUM>, two bearings <NUM> and <NUM>, a rack guide mechanism <NUM>, and a steering assistance device <NUM>. A driver who drives an automobile equipped with this column type electric power steering system <NUM> performs steering operations by turning the steering wheel <NUM>. The steering shaft <NUM> includes a column shaft <NUM>, a first universal joint <NUM>, an intermediate shaft <NUM>, and a second universal joint <NUM>. The first universal joint <NUM> includes a first yoke that is omitted from illustration, a plurality of first rolling elements that is omitted from illustration, a first joint spider that is omitted from illustration, a plurality of second rolling elements that is omitted from illustration, and a second yoke that is omitted from illustration. The second universal joint <NUM> includes a third yoke that is omitted from illustration, a plurality of third rolling elements that is omitted from illustration, a second joint spider that is omitted from illustration, a plurality of fourth rolling elements that is omitted from illustration, and a fourth yoke that is omitted from illustration.

The column shaft <NUM> fixes the steering wheel <NUM> at one end thereof in the extending direction. The column shaft <NUM> fixes the first yoke of the first universal joint <NUM> at the other end thereof in the extending direction. The column shaft <NUM> is rotatable about a central axis in the extending direction. The first yoke is pivotably fitted to a first pair of trunnions located on the same central axis of the first joint spider via the plurality of first rolling elements. The second yoke is pivotably fitted to a second pair of trunnions located on the same central axis of the first joint spider via the plurality of second rolling elements. The central axes of the first pair of trunnions and the central axes of the second trunnions intersect at an angle of <NUM> degrees.

The second yoke of the first universal joint <NUM> fixes one end of the intermediate shaft <NUM> in the extending direction thereof. The intermediate shaft <NUM> fixes the third yoke of the second universal joint <NUM> at the other end thereof in the extending direction. The third yoke is pivotably fitted to a third pair of trunnions located on the same central axis of the second joint spider via the plurality of third rolling elements. The fourth yoke is pivotably fitted to a fourth pair of trunnions located on the same central axis of the second joint spider via the plurality of fourth rolling elements. The central axes of the third pair of trunnions and the central axes of the fourth trunnions intersect at an angle of <NUM> degrees. The fourth yoke of the second universal joint <NUM> fixes one end of the pinion shaft <NUM> in the extending direction thereof. Thus, when the driver turns the steering wheel <NUM>, the column shaft <NUM> turns about the central axis in the extending direction thereof, the intermediate shaft <NUM> also turns about a central axis in the extending direction thereof, and the pinion shaft <NUM> also turns about a central axis in the extending direction thereof.

In the column type electric power steering system <NUM>, the pinion shaft <NUM>, the rack shaft <NUM>, the housing <NUM>, the two rack bushings <NUM> and <NUM>, the two bearings <NUM> and <NUM>, and the rack guide mechanism <NUM> make up the steering gear device <NUM> serving as a rack and pinion type steering device. In <FIG>, the housing <NUM> is represented by a hidden outline (long dashed double-short dashed line), and inside thereof is illustrated.

The pinion shaft <NUM> extends from the upper side to the lower side of the automobile in the vertical direction. The pinion shaft <NUM> includes, from one end side to the other end along the extending direction thereof, a serrated portion <NUM>, a shaft portion <NUM>, a pinion toothed portion <NUM>, and a boss portion <NUM>. Serrations are formed in the serrated portion <NUM>. The fourth yoke of the second universal joint <NUM> is fixed to the serrations of the serrated portion <NUM>. The shaft portion <NUM> has a cylindrical shape. Pinion teeth <NUM> are formed over the entire face of the pinion toothed portion <NUM> in the circumferential direction. An extending direction of the pinion teeth <NUM> has an angle that is not <NUM> degrees with respect to the extending direction of the central axis of the pinion shaft <NUM>. The boss portion <NUM> has a cylindrical shape.

The housing <NUM> has a first opening <NUM> on a steering wheel <NUM> side thereof, and a side opposite to the first opening <NUM> is sealed off. The pinion shaft <NUM> is accommodated within the housing <NUM>. The pinion shaft <NUM> is rotatably supported by the two bearings <NUM> and <NUM>, with respect to the housing <NUM>. The bearing <NUM> is a ball bearing. The bearing <NUM> includes an inner ring, an outer ring, and balls, with the inner ring being fixed to the shaft portion <NUM> and also the outer ring being fixed to the housing <NUM>, and the balls roll between the inner ring and the outer ring. The bearing <NUM> is a roller bearing. The bearing <NUM> includes rollers and an outer ring, with the outer ring being fixed to the housing <NUM>, and the rollers roll on an outer peripheral face of the boss portion <NUM> and the outer ring.

A lid <NUM>, through which the pinion shaft <NUM> passes in a state in which the pinion shaft <NUM>, the two bearings <NUM> and <NUM> are inserted into the housing <NUM>, is fixed to the first opening <NUM> of the housing. A seal is fixed to the lid <NUM>, and the seal is slidable on an outer peripheral face 722b of the shaft portion <NUM> of the pinion shaft <NUM>. A cover member <NUM> is further fixed to the housing <NUM>. The cover member <NUM> covers a portion of the shaft portion <NUM> of the pinion shaft <NUM> from the outside, in the radial direction.

The rack shaft <NUM> is provided with, from one end to the other end in an extending direction thereof, a first cylindrical portion <NUM>, a rack toothed portion <NUM>, and a second cylindrical portion <NUM>. The rack toothed portion <NUM> has rack teeth <NUM> formed on a portion thereof in the circumferential direction, and the other portion thereof in the circumferential direction is a cylindrical face <NUM> of which a central axis is the extending direction of the rack shaft <NUM>. An outer peripheral face of the first cylindrical portion <NUM> and an outer peripheral face of the second cylindrical portion <NUM> are each a cylindrical face of which the central axis are in the extending direction of the rack shaft <NUM>. The extending direction of the rack teeth <NUM> has an angle that is not <NUM> degrees with respect to the extending direction of the rack shaft <NUM>.

The housing <NUM> extends in a direction different from the first opening <NUM> on the steering wheel <NUM> side, and has a second opening <NUM> at one end in the extending direction and a third opening <NUM> at the other end thereof. The rack shaft <NUM> is accommodated within the housing <NUM>, along the direction in which the housing <NUM> extends. One end of the rack shaft <NUM> in the extending direction thereof protrudes from the second opening <NUM> at one end of the housing <NUM> in the extending direction thereof. The other end of the rack shaft <NUM> in the extending direction thereof protrudes from the third opening <NUM> at the other end of the housing <NUM> in the extending direction thereof.

The first rack bushing <NUM> is fixed to one end of the housing <NUM> in the extending direction. The first rack bushing <NUM> is fixed to the housing <NUM>, adjacent to the second opening <NUM>. The first rack bushing <NUM> is slidable on the outer peripheral face of the first cylindrical portion <NUM> of the rack shaft <NUM>. A second rack bushing <NUM> is fixed to the other end of the housing <NUM> in the extending direction. The second rack bushing <NUM> is fixed to the housing <NUM>, adjacent to the third opening <NUM>. The second rack bushing <NUM> is slidable on the outer peripheral face of the second cylindrical portion <NUM> of the rack shaft <NUM>.

The pinion teeth <NUM> formed on the pinion toothed portion <NUM> of the pinion shaft <NUM>, and the rack teeth <NUM> formed on the rack toothed portion <NUM> of the rack shaft <NUM> are capable of rolling-sliding contact via the grease composition G. The pinion teeth <NUM> and the rack teeth <NUM> are meshed with each other via the grease composition G. When the pinion shaft <NUM> turns relative to the housing <NUM> about the central axis in the extending direction thereof, the rack shaft <NUM> moves in the linear direction relative to the housing <NUM> in the extending direction of the housing <NUM>.

The housing <NUM> is fixed to an automobile that is omitted from illustration, with the extending direction of the housing <NUM> aligned with a vehicle-width direction. Ball joint sockets <NUM>, <NUM> are fixed to one end and the other end of the rack shaft <NUM>, respectively, and tie rods <NUM>, <NUM> connected to these ball joint sockets <NUM>, <NUM>, respectively, are connected to bearing rings of rolling bearings that rotatably support a right and left pair of front wheels <NUM>, <NUM> via knuckle arms <NUM>, <NUM>. Moving the rack shaft <NUM> in a linear direction, in the extending direction of the housing <NUM>, steers the right and left front wheels <NUM>, <NUM>, which are steered wheels.

The rack guide mechanism <NUM> is fixed to the housing <NUM>. The housing <NUM> has a fourth opening <NUM> at a cylindrical face <NUM> side that is the other portion of the rack toothed portion <NUM> of the rack shaft <NUM> in the circumferential direction, at a position where the pinion shaft <NUM> meshes with the rack shaft <NUM>, in the extending direction.

The rack guide mechanism <NUM> includes a support yoke <NUM>, a sheet member <NUM>, a coil spring <NUM>, and a plug <NUM>. The sheet member <NUM> is interposed between the cylindrical face <NUM>, which is the other portion of the rack toothed portion <NUM> of the rack shaft <NUM> in the circumferential direction, and a cylindrical face of the support yoke <NUM>. The sheet member <NUM> is fixed to the support yoke <NUM>. The sheet member <NUM> and the cylindrical face <NUM>, which is the other portion of the rack toothed portion <NUM> of the rack shaft <NUM> in the circumferential direction, are capable of sliding contact via the grease composition G. The plug <NUM> is fixed to the fourth opening <NUM> of the housing <NUM>. The plug <NUM> is in contact with one end of the coil spring <NUM>. The support yoke <NUM> is in contact with the other end of the coil spring <NUM>. The coil spring <NUM> is shorter than a free length thereof in a state in which the plug <NUM> is fixed to the fourth opening <NUM>. Thus, the sheet member <NUM> is pressed against the rack shaft <NUM> with respect to the housing <NUM>.

The steering assistance device <NUM> includes a controller <NUM>, a torque sensor <NUM> that detects steering torque applied by the driver to the steering wheel <NUM>, an electric motor <NUM>, and speed reducing mechanism <NUM> that reduces the rotational force of the output shaft <NUM> of the electric motor <NUM> and performs transmission thereof to the column shaft <NUM>. The speed reducing mechanism <NUM> is an assembly in which a worm <NUM> that rotates integrally with the output shaft <NUM> of the electric motor <NUM> and a worm wheel <NUM> that rotates integrally with the column shaft <NUM> mesh with each other. A motor current is supplied to the electric motor <NUM> from the controller <NUM>. The controller <NUM> controls the electric motor <NUM> based on the steering torque detected by the torque sensor <NUM>, vehicle speed, and so forth, and applies the rotational force of the output shaft <NUM> of the electric motor <NUM>, of which speed is reduced by the speed reducing mechanism <NUM>, to the column shaft <NUM> as a steering assisting force.

The grease composition G is sealed within the housing <NUM>. The grease composition G is interposed between rolling and sliding faces of the pinion teeth <NUM> and rolling and sliding faces of the rack teeth <NUM>, which are in contact with each other when the pinion teeth <NUM> and the rack teeth <NUM> mesh with each other, thereby lubricating between the rolling and sliding faces of both. The grease composition G is interposed between a sliding face of the sheet member <NUM> and a sliding face of the cylindrical face <NUM>, which is the other portion of the rack toothed portion <NUM> of the rack shaft <NUM> in the circumferential direction, where the sheet member <NUM> and the rack shaft <NUM> come into contact by being pressed against each other, thereby lubricating between both sliding faces.

<FIG> is a cross-sectional view of a ball bearing <NUM>, which is an example of a rolling bearing.

The ball bearing <NUM> includes an inner ring <NUM>, an outer ring <NUM> provided on an outer side of the inner ring <NUM> in a radial direction, balls <NUM> serving as a plurality of rolling elements provided between the inner ring <NUM> and the outer ring <NUM>, and a cage <NUM> that is annular in shape and that holds these balls <NUM>. Also, seals <NUM> are provided on each of one side and the other side in an axial direction of the ball bearing <NUM>.

Further, the grease composition G is sealed in an annular region <NUM> between the inner ring <NUM> and the outer ring <NUM>.

The inner ring <NUM> has an inner raceway face <NUM> formed on an outer periphery thereof, on which the balls <NUM> roll.

The outer ring <NUM> has an outer raceway face <NUM> formed on an inner periphery thereof, on which the balls <NUM> roll.

A plurality of the balls <NUM> is interposed between the inner raceway face <NUM> and the outer raceway face <NUM>, and rolls on the inner raceway face <NUM> and the outer raceway face <NUM>. The grease composition G sealed in the region <NUM> is also interposed at contact portions between the balls <NUM> and the inner raceway face <NUM> of the inner ring <NUM>, and at contact portions between the balls <NUM> and the outer raceway face <NUM> of the outer ring <NUM>. Note that the grease composition G is sealed in so as to occupy <NUM>% by volume or more and <NUM>% by volume or less of volume of a space surrounded by the inner ring <NUM>, the outer ring <NUM>, and the seals <NUM>, excluding the balls <NUM> and the cage <NUM>.

The seals <NUM> are members that are annular and that include a core 806a that is annular, and an elastic member 806b fixed to the core 806a, with a radial-direction outer-side portion fixed to the outer ring <NUM>, and a radial-direction inner-side portion slidably attached onto the inner ring <NUM>. The seals <NUM> prevent the grease composition G that is sealed in from externally leaking.

The ball bearing <NUM> configured in this way has the grease composition according to the present disclosure sealed therein as the grease composition G. The grease composition according to the present disclosure ensures oil retention properties, and accordingly the ball bearing <NUM> has good seizure resistance and wear resistance.

The grease composition according to the present disclosure can be sealed in and used with the above-described dual-pinion type electric power steering systems, column type electric power steering systems, rolling bearings, and so forth.

The grease composition according to an embodiment of the present disclosure includes a base oil and a thickener, and the thickener includes a urea compound and a styrene-based polymer.

Examples of the base oil include poly-α-olefin (PAO), ester oil, polyalkylene glycol, fluorine oil, silicone oil, ether oil, and so forth.

Among these, poly-α-olefin (PAO) is preferred. This is because the above grease composition has good low-temperature fluidity by using poly-α-olefin. This is also because the grease composition exhibits little aggression with respect to members made of rubber or made of resin.

Examples of the poly-α-olefin include oligomerized or polymerized α-olefins such as <NUM>-hexene, <NUM>-octene, <NUM>-nonene, <NUM>-decene, <NUM>-dodecene, and <NUM>-tetradecene, or the like, and further hydrides thereof.

As for the poly-α-olefin, PAO4 to PAO8, which are oligomerized <NUM>-decene, are preferable.

The base oil kinematic viscosity of the base oil at <NUM> is preferably <NUM><NUM>/s or more and <NUM><NUM>/s or less. In this case, the grease composition is suitable for achieving low torque.

The base oil kinematic viscosity (<NUM>) is more preferably <NUM><NUM>/s or more and <NUM><NUM>/s or less.

The above base oil kinematic viscosity is a value conforming to JIS K <NUM>.

The thickener is a blended substance containing a urea compound and a styrene-based polymer. When the grease composition contains a thickener containing a urea compound and a styrene-based polymer, the grease composition has good oil retention properties and is suitable for ensuring low torque performance.

Examples of the urea compound include urea compounds such as diurea, triurea, tetraurea, and polyurea (excluding diurea, triurea, and tetraurea), and so forth, urea/urethane compounds, urethane compounds such as diurethane and so forth, blended substances thereof, and so forth.

As for the urea compound, diurea represented by the following Structural Formula (<NUM>) is preferable, with regard to the point that the grease composition has good heat resistance.

R<NUM> - NHCONH - R<NUM> - NHCONH - R<NUM> · · ·     (<NUM>).

(In Formula (<NUM>), R<NUM> and R<NUM> represent amino residues, independently from each other, and R<NUM> represents a diisocyanate residue.

Diurea represented by the above Structural Formula (<NUM>) is a reaction product of an amine compound and a diisocyanate compound.

The amine compound may be any one that is known to be an amine compound for synthesizing diurea, which is known as a thickener.

Examples of the amine compounds include alkylamines, alkylphenylamines, cyclohexylamines, and so forth.

Among these, alkylamines are preferred, with respect to the point that the grease composition has good low torque properties, and the point that the grease composition has good heat resistance.

The diisocyanate compound may be any diisocyanate compound that is known to be a diisocyanate compound for synthesizing diurea, which is known as a thickener. Examples of the diisocyanate compound include <NUM>,<NUM>-toluene diisocyanate (<NUM>,<NUM>-TDI), <NUM>,<NUM>-toluene diisocyanate (<NUM>,<NUM>-TDI), a blended substance of <NUM>,<NUM>-TDI and <NUM>,<NUM>-TDI, <NUM>,<NUM>'-diphenylmethane diisocyanate (MDI), and so forth.

The content of the thickener is preferably <NUM>% by mass or more and <NUM>% by mass or less as to the total amount of the base oil and the thickener.

The reason thereof is that the grease composition has good low torque properties.

In order to obtain the diurea represented by the above Structural Formula (<NUM>), reaction of the amine compound and the diisocyanate compound can be carried out under various conditions. The above reaction may be carried out, for example, (a) in a base oil, or (b) in a solvent. When carried out in a base oil, the blended substance following the reaction can be used as the grease composition. When carried out in a solvent, the grease composition can be obtained by removing the solvent to obtain diurea in powder form, following which the diurea in powder form is blended with a base oil. A production method for the grease composition will be described in detail later.

The styrene-based polymer is a polymer containing styrene or a derivative thereof as a monomer component.

The styrene-based polymer may be a homopolymer of styrene or a derivative thereof, or a copolymer of a first monomer component selected from among styrene and derivatives thereof and another monomer component. The other monomer component may be styrene or a derivative thereof, as long as it is different from the first monomer component.

Examples of the copolymer include random copolymerization, alternating copolymerization, block copolymerization, and graft copolymers.

Examples of the styrene homopolymer include atactic polystyrene, isotactic polystyrene, poly-p-methylstyrene, poly-p-ethylstyrene, poly-p-isopropylstyrene, poly-α-methylstyrene, and so forth.

Examples of the copolymer include a copolymer of a first monomer component selected from styrene and derivatives thereof, and styrene or a derivative thereof other than the first monomer component.

Examples of the copolymer also include a copolymer of the first monomer component and an alkadiene. Examples of the alkadiene include butadiene, isoprene, pentadiene, hexadiene, and so forth.

In the above styrene-isoprene copolymer, the ratio (molar ratio) of styrene and isoprene can be styrene : isoprene = <NUM>:<NUM> to <NUM>:<NUM>.

The copolymer is not limited to a copolymer of two types of monomer components, and may be a copolymer of three or more types of monomer components.

The number average molecular weight of the styrene-based polymer is preferably <NUM>,<NUM> or more and <NUM>,<NUM> or less, and more preferably <NUM>,<NUM> or more and <NUM>,<NUM> or less. Measurement of the above number average molecular weight is performed using gel permeation chromatography.

Commercially available products can also be used for the styrene-based polymer. Specific examples of commercially available products include Lubrizol (registered trademark) <NUM> (manufactured by The Lubrizol Corporation), <NUM> of the same, <NUM> of the same, Infineum (registered trademark) SV140 (manufactured by Infineum International Limited), <NUM> of the same, <NUM> of the same, Septon (registered trademark) <NUM> (manufactured by Kuraray Co. ), <NUM> of the same, and so forth.

The content of the styrene-based polymer is <NUM>% by mass or more and <NUM>% by mass or less as to the total amount of the urea compound and the styrene-based polymer. When the content of the styrene-based polymer is less than <NUM>% by mass, the grease composition has neither good oil retention properties nor good low torque properties. On the other hand, the oil retention properties of the grease composition will hardly improve even when the content thereof exceeds <NUM>% by mass.

The content of the styrene-based polymer is preferably <NUM>% by mass or more and <NUM>% by mass or less as to the total amount of the urea compound and the styrene-based polymer, from the perspective of ensuring good oil retention properties and good low torque properties, and more preferably <NUM>% by mass or more and <NUM>% by mass or less.

In the above grease composition, the particles of the thickener that have diameters of <NUM> or more have an average value of diameter of <NUM> or more and <NUM> or less. The average value of the diameter of the thickener is the average value of the diameter calculated from the volume of the particles, assuming the shape of the particles of the thickener to be a true sphere.

The diameter of the particles of the thickener is measured using a confocal laser microscope using a laser beam with a wavelength of <NUM> as excitation light.

When observing the thickener using a confocal laser microscope, particles with a diameter of less than <NUM> cannot be observed, due to the resolution of the confocal laser microscope. Accordingly, in the grease composition of the present disclosure, the average value of the diameter of the thickener is defined as the average value of the diameter of the particles of the thickener with a diameter of <NUM> or more.

This does not mean that the above grease composition does not contain particles of thickener less than <NUM> in diameter.

When the above grease composition is irradiated with a laser beam having a wavelength of <NUM>, the urea compound making up the thickener emits fluorescence, and accordingly the urea compound is observed as a fluorescent image. Also, in the grease composition, the styrene-based polymer is present in a state of being entangled with the urea compound. Accordingly, in the grease composition of the present disclosure, the fluorescence image of the urea compound observed with a confocal laser microscope is regarded as being a fluorescence image of the thickener particles.

Also, in the above observation, the volume of the thickener particles is measured, the diameter of the thickener particles is calculated from the measured volume assuming the shape of the thickener particles to be a true sphere, and the average value thereof is calculated. The average value of the diameter can be calculated using commercially available analysis software.

The particles of the thickener that have diameters of <NUM> or more have an average value of diameter of <NUM> or more and <NUM> or less, thereby enabling both of ensuring oil retention properties and improving low torque performance.

When the average value of the diameter exceeds <NUM>, oil retention properties and low torque performance will deteriorate.

On the other hand, thickener particles with a diameter of less than <NUM> cannot be observed, as described above, and accordingly the lower limit of the average diameter is <NUM>.

The above grease composition may contain additives to the extent that the effects of the invention of the present disclosure are not impaired. Examples of the above additives include antioxidants, rust inhibitors, extreme pressure agents, anti-wear agents, dyes, hue stabilizers, viscosity improvers, structural stabilizers, metal deactivators, viscosity index improvers, and so forth.

When the grease composition contains additives, the total content of the additives in the grease composition is preferably <NUM>% by mass or less as to the total mass of the base oil and the thickener.

As described above, the grease composition according to the present disclosure can be suitably used, for example, as a grease composition or the like that is sealed in gears such as electric power steering gears or the like of automobiles, rolling bearings, and so forth.

Methods of producing the grease composition according to the present disclosure that can be employed include (a) a method of synthesizing a urea compound in a solvent, and thereafter blending the obtained urea compound with a base oil (hereinafter also referred to as production method A), and (b) a method of synthesizing a urea compound in a base oil (hereinafter also referred to as production method B).

The urea compound can be synthesized by blending an amine compound and an isocyanate compound at a predetermined molar ratio, and causing reaction of the amine compound and the isocyanate compound. Production methods of the above grease composition will be described below by way of an example of a case in which a diisocyanate compound is used as the isocyanate compound, and diurea is synthesized as the urea compound.

As specific embodiments of production method A, for example, production methods A1 to A3 can be exemplified.

<FIG> is a flowchart for describing a production method A1 of the grease composition. (<NUM>) In production method A1, first, predetermined amounts of each of an amine compound, a diisocyanate compound, a styrene-based polymer, a solvent A, and a solvent B are provided. Specific examples of the amine compound, the diisocyanate compound, and the styrene-based polymer are as described above.

Preferably, each of the solvent A and the solvent B has a boiling point that is lower than that of the provided styrene-based polymer, and is capable of dissolving the styrene-based polymer that is provided.

Specific examples of the solvent A and the solvent B include toluene, hexane, ethyl acetate, tetrahydrofuran, p-xylene, m-xylene, o-xylene, methyl acetate and so forth. Note that it is preferable to avoid using substances that will react with substances having isocyanate groups, such as substances having amine groups, substances having hydroxyl groups, and so forth, or substances that will react with substances having amine groups, as the above solvent A and solvent B.

The solvent A and the solvent B preferably have a lower viscosity than the styrene-based polymer that is provided.

In the present disclosure, the viscosities of the solvents and the styrene-based polymer are measured using a Cannon-Fenske viscometer, in accordance with the method of JIS Z <NUM>:<NUM>.

The solvent A and the solvent B may be the same or may be different, but are preferably the same.

When a blended solution A containing the solvent A and a blended solution B containing the solvent B are blended in a latter process, the two are blended in a sure manner, which is suitable for promoting the reaction between the amine compound and the diisocyanate compound. Moreover, when removing the solvent A and the solvent B in a subsequent process, selection of the removal method and removal conditions is facilitated.

(<NUM>) Next, a portion of the styrene-based polymer and the amine compound are added to the solvent A to obtain a blended solution A (S111).

At this time, the timing of adding the styrene-based polymer and the amine compound to the solvent A is not limited in particular, and (a) the styrene-based polymer may be dissolved in the solvent A to prepare a solution, following which the amine compound is dissolved or dispersed in the obtained solution, thereby yielding the blended solution A, (b) the amine compound may be dissolved or dispersed in the solvent A to prepare a blended solution, following which the styrene-based polymer is dissolved in the obtained blended solution, thereby yielding the blended solution A, or (c) the amine compound and the styrene-based polymer may be added to the solvent A at the same time, following which all the components are blended to yield the blended solution A.

At this time, the amount of the amine compound can be, for example, <NUM>% by mass or more and <NUM>% by mass or less as to <NUM>% by mass of the solvent A.

Also, the amount of the styrene-based polymer can be, for example, <NUM>% by mass or more and <NUM>% by mass or less as to <NUM>% by mass of the solvent A.

(<NUM>) Separately from the process of (<NUM>) above, the remaining styrene-based polymer and diisocyanate compound are added to the solvent B to obtain the blended solution B (S112).

At this time, the timing of adding the styrene-based polymer and the diisocyanate compound to the solvent B is not limited in particular, and (a) the styrene-based polymer may be dissolved in the solvent B to prepare a solution, following which the diisocyanate compound is dissolved or dispersed in the obtained solution, thereby yielding the blended solution B, (b) the diisocyanate compound may be dissolved or dispersed in solvent B to prepare a blended solution, following which the styrene-based polymer is dissolved in the obtained blended solution, thereby yielding the blended solution B, or (c) the diisocyanate compound and the styrene-based polymer may be added to the solvent B at the same time, following which all the components are blended to yield the blended solution B.

At this time, the amount of the diisocyanate compound can be, for example, <NUM>% by mass or more and <NUM>% by mass or less as to <NUM>% by mass of the solvent B.

Also, the amount of the styrene-based polymer can be, for example, <NUM>% by mass or more and <NUM>% by mass or less as to <NUM>% by mass of the solvent B.

(<NUM>) Next, the blended solution A and the blended solution B are blended, and reaction of the amine compound and the diisocyanate compound is carried out, so as to synthesize diurea (S113).

Here, the blended solution B may be added dropwise to the blended solution A while stirring the blended solution A, thereby blending the two, or the blended solution A may be added dropwise to the blended solution B while stirring the blended solution B, thereby blending the two.

The blended solution A and the blended solution B may be blended at room temperature or under heat.

When performing under heat, the heating temperature can be, for example, <NUM> or higher and <NUM> or lower.

The blended solution A and the blended solution B may be blended such that <NUM> mol of the diisocyanate compound is blended as to <NUM> to <NUM> mol of the amine compound. The duration of reaction of the amine compound and the diisocyanate compound is not limited in particular, and may be any duration that allows the reaction to proceed sufficiently. Specifically, the duration may be, for example, <NUM> hours or more and <NUM> hours or less.

In the processes of (<NUM>) to (<NUM>) above, the blending of the amine compound, the diisocyanate compound, and the styrene-based polymer into their respective solvents, and the blending of the blended solution A and the blended solution B can be carried out using, for example, a mechanical stirrer, a magnet stirrer, or the like. Among these, a method using a mechanical stirrer is preferable due to facilitating uniform blending of each component.

Going through such processes of (<NUM>) to (<NUM>) enables a blended substance containing diurea, styrene-based polymer, and solvent A and solvent B, to be obtained.

(<NUM>) The solvent A and the solvent B are removed from the blended substance obtained in the process of (<NUM>) above (S114).

The method for removing the solvent A and the solvent B is not limited in particular, and the solvent A and the solvent B can be vaporized at room temperature, or while appropriately performing heating, pressure reduction, stirring, and so forth, as necessary. Specific methods can be selected as appropriate, depending on the types of the solvent A and the solvent B, and the following methods can be exemplified.

One example of a method is to let the blended substance stand at room temperature and atmospheric pressure to vaporize the solvent A and the solvent B.

Also, for example, another method that can be given is to heat the blended substance under atmospheric pressure at a temperature lower than the boiling points of the solvent A and the solvent B, to vaporize the solvent A and the solvent B. In this case, heating conditions that can be exemplified include performing heating under atmospheric pressure in a constant temperature bath at <NUM> for <NUM> hours or more and <NUM> hours or less, or the like, for example. These methods may be combined.

(<NUM>) Next, the blended substance that remains after removing the solvent A and the solvent B is washed (S115).

Performing this washing process enables unreacted amine compounds and diisocyanate compounds remaining in the blended substance to be removed.

Specific examples of the cleaning method here include the following method, for example. First, the blended substance following the removal of the solvent A and the solvent B therefrom is blended with water, filtered with a membrane filter, and residue is collected. Thereafter, the residue is heated at a temperature lower than the boiling point of water, and lower than the boiling point of the styrene-based polymer, so as to vaporize water adhering to the residue, and thus remove water from the residue. In this case, heating conditions that can be exemplified include performing heating under atmospheric pressure in a high-temperature bath at <NUM> for <NUM> hours or more and <NUM> hours or less, or the like, for example.

(<NUM>) The blended substance that is washed is collected to obtain a blended substance C containing diurea and styrene-based polymer (S116).

The blended substance C that is obtained may be subjected to pulverization processing of diurea, as necessary. Performing the pulverization processing enables the thickener to be made finer and more uniform.

The above pulverization processing is preferably performed using a small-sized pulverizer (e.g., Labo Millser manufactured by Osaka Chemical Co. , or the like), because the pulverization processing can be performed with a simple device and at low costs.

(<NUM>) Next, base oil is added to the blended substance C containing diurea and styrene-based polymer, and the two are blended (S117).

Specific examples of the base oil are as described above.

Here, the blended substance C may be added dropwise to the base oil while stirring the base oil, to blend the two, or the base oil may be added dropwise to the blended substance C while stirring the blended substance C, to blend the two.

The blended substance C and the base oil are preferably blended under heat. At this time, the heating temperature may be, for example, <NUM> or higher and <NUM> or lower.

The blending duration of the blended substance C and the base oil is not limited in particular, and may be, for example, <NUM> hours or more and <NUM> hours or less.

The method of blending the blended substance C and the base oil is not limited in particular, as long as both are blended uniformly, and examples thereof include a method using a mechanical stirrer or a magnetic stirrer, or the like. Among these, a method using a mechanical stirrer is preferable due to facilitating uniform blending of the two.

The above grease composition can be produced through such processes.

<FIG> is a flowchart for describing a production method A2 of the grease composition. (<NUM>) In production method A2, first, predetermined amounts of each of the amine compound, the diisocyanate compound, the styrene-based polymer, the solvent A, and the solvent B are provided.

Specific examples and suitable examples of the amine compound, the diisocyanate compound, and the styrene-based polymer are as described above.

Specific examples, preferred examples, and examples preferably avoided, regarding the solvent A and the solvent B, are the same as those for production method A1. The solvent A and the solvent B may be the same or may be different, but are preferably the same.

(<NUM>) Next, the amine compound is added to the solvent A to obtain a blended solution A' (S121).

At this time, the amount of the amine compound may be, for example, <NUM>% by mass or more and <NUM>% by mass or less as to <NUM>% by mass of the solvent A.

(<NUM>) Separately from the process of (<NUM>) above, the styrene-based polymer and the diisocyanate compound are added to the solvent B to obtain the blended solution B (S122).

(<NUM>) Next, the blended solution A' and the blended solution B are blended, and reaction of the amine compound and the diisocyanate compound is carried out, so as to synthesize diurea (S123).

This process can be performed in the same way as the process of (<NUM>) in production method A1, except that the blended solution A is replaced with the blended solution A'.

In the processes of (<NUM>) to (<NUM>) above, the blending of the amine compound, the diisocyanate compound, and the styrene-based polymer into their respective solvents, and the blending of the blended solution A' and the blended solution B can be carried out using, for example, a mechanical stirrer, a magnet stirrer, or the like. Among these, a method using a mechanical stirrer is preferable due to facilitating uniform blending of each component.

(<NUM>) The solvent A and the solvent B are removed from the blended substance obtained in the process of (<NUM>) above (S124).

This process can be performed in the same way as the process of (<NUM>) in production method A1.

(<NUM>) Next, the blended substance that remains after removing the solvent A and the solvent B is washed (S125).

(<NUM>) The blended substance that is washed is collected to obtain a blended substance C containing diurea and styrene-based polymer (S126).

(<NUM>) Next, base oil is added to the blended substance C containing diurea and styrene-based polymer, and the two are blended (S127).

The blended substance C and the base oil may be blended in the same way as in process of (<NUM>) in production method A1.

The above grease composition can be produced through such processes as well.

<FIG> is a flowchart for describing a production method A3 of the grease composition.

(<NUM>) Next, the styrene-based polymer and the amine compound are added to the solvent A to obtain a blended solution A (S131).

Also, the amount of the styrene-based polymer may be, for example, <NUM>% by mass or more and <NUM>% by mass or less as to <NUM>% by mass of the solvent A.

(<NUM>) Separately from the process of (<NUM>) above, the diisocyanate compound is added to the solvent B to obtain a blended solution B' (S132).

(<NUM>) Next, the blended solution A and the blended solution B' are blended, and reaction of the amine compound and the diisocyanate compound is carried out, so as to synthesize diurea (S133).

This process can be performed in the same way as the process of (<NUM>) in production method A1, except that the blended solution B is replaced with the blended solution B'.

In the processes of (<NUM>) to (<NUM>) above, the blending of the amine compound, the diisocyanate compound, and the styrene-based polymer into their respective solvents, and the blending of the blended solution A and the blended solution B' can be carried out using, for example, a mechanical stirrer, a magnet stirrer, or the like. Among these, a method using a mechanical stirrer is preferable due to facilitating uniform blending of each component.

(<NUM>) The solvent A and the solvent B are removed from the blended substance obtained in the process of (<NUM>) above (S134).

(<NUM>) Next, the blended substance that remains after removing the solvent A and the solvent B is washed (S135).

(<NUM>) The blended substance that is washed is collected to obtain a blended substance C containing diurea and styrene-based polymer (S136).

(<NUM>) Next, base oil is added to the blended substance C containing diurea and styrene-based polymer, and the two are blended (S137).

In production methods A1 to A3, homogenization processing using a roll mill or the like may be performed as necessary, after blending the blended substance C and the base oil.

Also, when producing a grease composition containing additives in addition to the blended substance C and the base oil, for example, necessary additives may be blended therein after blending the base oil and the blended substance C, or the blended substance C and the necessary additives may be blended into the base oil at the same time.

(c) The order of the process of removing the solvent A and the solvent B (S114, S124, S134) and the process of washing the blended substance (S115, S125, S135) may be reversed. In this case, for example, the following method, or the like, can be employed.

The above blended substance in which diurea is dispersed in the solvent A and the solvent B is placed in a separatory funnel, water is further placed in this separatory funnel, and unreacted amine compounds and unreacted diisocyanate compounds are transferred to the water phase. Next, the water containing the unreacted amine compounds and diisocyanate compounds is removed from the separatory funnel. Thereafter, the solvent A and the solvent B are removed from the above blended substance that has been washed using the separatory funnel, by the method of the process for removing the solvent A and the solvent B (S114, S124, S134).

The process of washing the blended substance (S115, S125, S135) is not an essential process, and may be omitted.

After performing the process of synthesizing diurea (S113, S123, S133), and before the process of removing the solvent A and the solvent B (S114, S124, S134), the base oil may also be added to the blended substance obtained in the process of synthesizing diurea. In this case, the process of adding the base oil to the blended substance C (S117, S127, S137) becomes unnecessary.

Production method A, which includes the process of synthesizing diurea in the presence of a styrene-based polymer, is suitable as a method for manufacturing a grease composition that has good oil retention properties and can ensure low torque performance.

As specific embodiments of production method B, for example, production methods B1 to B3 can be exemplified.

<FIG> is a flowchart for describing a production method B1 of the grease composition.

The blended solution D and the blended solution E may be blended at room temperature or under heat.

The blended solution D and the blended solution E may be blended such that <NUM> mol of the diisocyanate compound is blended as to <NUM> to <NUM> mol of the amine compound.

The duration of reaction of the amine compound and the diisocyanate compound is not limited in particular, and may be any duration that allows the reaction to proceed sufficiently. Specifically, the duration may be, for example, <NUM> hours or more and <NUM> hours or less.

In the processes of (<NUM>) to (<NUM>) above, the blending of the amine compound, the diisocyanate compound, and the styrene-based polymer into their respective base oils, and the blending of the blended solution D and the blended solution E can be carried out using, for example, a mechanical stirrer, a magnet stirrer, or the like. Among these, a method using a mechanical stirrer is preferable due to facilitating uniform blending of each component.

By going through the processes of (<NUM>) to (<NUM>), a grease composition containing diurea and styrene-based polymer in the base oil can be produced.

<FIG> is a flowchart for describing a production method B2 of the grease composition.

In the processes of (<NUM>) to (<NUM>) above, the blending of the amine compound, the diisocyanate compound, and the styrene-based polymer into their respective base oils, and the blending of the blended solution D' and the blended solution E can be carried out using, for example, a mechanical stirrer, a magnet stirrer, or the like. Among these, a method using a mechanical stirrer is preferable due to facilitating uniform blending of each component.

A grease composition containing diurea and styrene-based polymer in the base oil can be produced by going through such processes of (<NUM>) to (<NUM>) as well.

<FIG> is a flowchart for describing a production method B3 of the grease composition.

In the processes of (<NUM>) to (<NUM>) above, the blending of the amine compound, the diisocyanate compound, and the styrene-based polymer into their respective base oils, and the blending of the blended solution D and the blended solution E' can be carried out using, for example, a mechanical stirrer, a magnet stirrer, or the like. Among these, a method using a mechanical stirrer is preferable due to facilitating uniform blending of each component.

In production methods B1 to B3, homogenization processing using a roll mill or the like may be performed as necessary, after diurea is synthesized.

Also, when producing a grease composition containing additives in addition to the base oil, the diurea, and the styrene-based polymer, for example, necessary additives may be blended in following synthesizing of diurea.

In production method B1, the amount of styrene-based polymer mixed in the blended solution D and the amount of styrene-based polymer blended in the blended solution E may be the same or may be different.

In production methods B1 to B3, the amount of base oil to which the amine compound is added and the amount of base oil to which the isocyanate compound is added may be different.

In processes of (<NUM>) to (<NUM>) of production method B1, after preparing the blended solution D' in which the base oil is blended with the amine compound, and the blended solution E' in which the base oil is blended with the diisocyanate compound, the blended solution D', the blended solution E', and the styrene-based polymer may be blended.

Production method B, which includes the process of synthesizing diurea in the presence of such a styrene-based polymer, is also suitable as a method for manufacturing a grease composition that has good oil retention properties and can ensure low torque performance.

Next, the invention according to the present disclosure will be described in more detail based on Examples, but it should be noted that the invention according to the present disclosure is not limited to the Examples alone.

In the Examples / Comparative Examples, the following raw materials were used.

Now, the amount of styrene-isoprene copolymer added to obtain the blended solution A1 and the amount of styrene-isoprene copolymer added to obtain the blended solution B1 were set to be the same.

In the processes of (<NUM>) and (<NUM>), the amounts of the octylamine and the MDI were set to be such that the mixing ratio of the two (octylamine : MDI) was <NUM>:<NUM> in molar ratio, and the amount of diurea generated was an amount that was <NUM>% by mass as to <NUM>% by mass of the toluene.

Also, the amount of styrene-isoprene copolymer added was such that the amount of styrene-isoprene copolymer contained in a later-described blended substance C of diurea and styrene-isoprene copolymer was set to be <NUM>% by mass as to the total amount of diurea and styrene-isoprene copolymer.

The blended solution A1 was prepared by adding the styrene-isoprene copolymer and the octylamine while stirring the toluene with a mechanical stirrer.

Also, the blended solution B1 was prepared by adding the styrene-isoprene copolymer and the MDI while stirring the toluene with a mechanical stirrer.

(<NUM>) The blended solution B1 was added dropwise to the blended solution A1 while stirring the blended solution A1 with a mechanical stirrer, thereby blending the two. After the dropwise addition of the blended solution B1 was completed, reaction of the octylamine and the MDI was carried out at room temperature while stirring for <NUM> hours to generate diurea.

(<NUM>) Thereafter, the blended substance containing diurea, styrene-isoprene copolymer, and toluene was left standing at room temperature for <NUM> hours, and the toluene was evaporated and removed, thereby producing the blended substance C of diurea and styrene-isoprene copolymer (thickener).

(<NUM>) The blended substance C at room temperature was added to the PAO8 as a base oil at room temperature, and heated to <NUM> while stirring with a mechanical stirrer. The base oil into which the blended substance C was blended was continuously stirred with a mechanical stirrer for <NUM> minutes, while maintained at <NUM>. Thereafter, the blended substance was allowed to cool in still air to room temperature while stirring with the mechanical stirrer, and the stirring was then stopped.

At this time, the amount of the PAO8 (base oil) was set to be <NUM>% by mass as to the total amount of the PAO8 and the blended substance C.

Thereafter, homogenization processing was performed using a roll mill, thus completing the grease composition.

The diurea generated in this example has the following Structural Formula.

A grease composition was completed in the same way as in Example <NUM>, except for the amount of styrene-isoprene copolymer added being changed such that the amount of styrene-isoprene copolymer contained in the blended substance C was set to be <NUM>% by mass as to the total amount of diurea and styrene-isoprene copolymer.

The blended solution A2 was prepared by adding octylamine to toluene while stirring the toluene with a mechanical stirrer.

Also, the blended solution B1 was prepared by adding MDI to toluene while stirring the toluene with a mechanical stirrer.

(<NUM>) The blended solution B2 was added dropwise to the blended solution A2 while stirring the blended solution A2 with a mechanical stirrer, thereby blending the two. After the dropwise addition of the blended solution B2 was completed, reaction of the octylamine and the MDI was carried out at room temperature while stirring for <NUM> hours to generate diurea.

(<NUM>) Thereafter, the blended substance containing diurea and toluene was left standing at room temperature for <NUM> hours, and the toluene was evaporated and removed, thereby producing diurea (thickener).

(<NUM>) The room temperature diurea obtained in (<NUM>) was added to the PAO8 as a base oil at room temperature, and heated to <NUM> while stirring with a mechanical stirrer. The base oil into which the diurea was blended was continuously stirred with a mechanical stirrer for <NUM> minutes, while maintained at <NUM>. Thereafter, the blended solution was allowed to cool in still air to room temperature while stirring with the mechanical stirrer, and the stirring was then stopped.

The Structural Formula of the diurea generated in the present Comparative Example <NUM> is the same as that in Example <NUM>.

The grease composition produced in Comparative Example <NUM> does not contain styrene-isoprene copolymers.

A grease composition was completed in the same way as in Example <NUM>, except that an acrylic-based polymer (alkyl-methacrylate-based copolymer) was mixed in instead of the styrene-isoprene copolymer.

At this time, the amount of the PAO8 (base oil) was set to be <NUM>% by mass as to the total amount of the PAO8, the styrene-isoprene copolymer, and the diurea. The amount of the styrene-isoprene copolymer was set to be <NUM>% by mass as to the total amount of the styrene-isoprene copolymer and diurea.

Now, the amount of base oil was set to be an amount that was <NUM>% by mass as to the total amount of the PAO8 and the thickener (styrene-isoprene copolymer and diurea generated through a later process).

Also, the amount of the styrene-isoprene copolymer was set to be <NUM>% by mass as to the total amount of the styrene-isoprene copolymer and the diurea that was generated.

(<NUM>) Half of the base oil (<NUM>), half of the styrene-isoprene copolymer, and the octylamine were placed in a stainless steel container A, and the blended substance was stirred at <NUM> for <NUM> minutes to obtain a blended solution D1. (<NUM>) Into another stainless steel container B were placed the remaining half of the base oil (<NUM>), the remaining half of the styrene-isoprene copolymer, and the MDI, and stirred at <NUM> for <NUM> minutes, thereby obtaining a blended solution E1.

(<NUM>) The blended solution D1 containing octylamine in the stainless steel container A was added dropwise into the stainless steel container B, and gradually introduced into the blended solution E1 containing the MDI.

(<NUM>) After confirming that the entire amount of the blended solution D1 in the stainless steel container A was introduced into the stainless steel container B, the temperature was raised to <NUM>.

(<NUM>) Stirring was performed while heating, and the temperature was maintained at <NUM> for <NUM> minutes.

(<NUM>) The heating was stopped, and the blended solution was allowed to cool in still air to <NUM>, while stirring.

(<NUM>) After confirming that the temperature was no higher than <NUM>, stirring was stopped and the blended solution was allowed to cool in still air, in that state, to room temperature.

(<NUM>) Homogenization processing was performed using a roll mill, thereby completing a grease composition.

Now, the amount of base oil was set to be an amount that was <NUM>% by mass as to the total amount of the PAO8 and the thickener (diurea generated through a later process).

(<NUM>) Half of the base oil (<NUM>) and the octylamine were placed in a stainless steel container A, and stirred at <NUM> for <NUM> minutes to obtain a blended solution D2.

(<NUM>) Into another stainless steel container B were placed the remaining half of the base oil (<NUM>) and the MDI, and stirred at <NUM> for <NUM> minutes, thereby obtaining a blended solution E2.

(<NUM>) The blended solution D2 containing octylamine in the stainless steel container A was added dropwise into the stainless steel container B, and gradually introduced into the blended solution E2 containing the MDI.

(<NUM>) After confirming that the entire amount of the blended solution D2 in the stainless steel container A was introduced into the stainless steel container B, the temperature was raised to <NUM>.

The grease composition produced in Comparative Example <NUM> does not contain a styrene-isoprene copolymer.

The grease compositions produced in the Examples and the Comparative Examples were evaluated as follows. The results are shown in Table <NUM>.

The worked penetration (60W) of the grease compositions produced in the Examples and the Comparative Examples was measured by a method conforming to JIS K <NUM>.

The oil separation degree of the grease compositions produced in the Examples and the Comparative Examples (excluding the grease compositions of Comparative Examples <NUM> and <NUM>) was measured using a method conforming to JIS K <NUM>. The results are shown in Table <NUM>.

At this time, the sample amount was <NUM>, the test temperature was <NUM>, and the test duration was <NUM> hours. The number of samples was <NUM>, and the average value thereof was used as the evaluation result.

The bearing running torque of the grease compositions prepared in the Examples and the Comparative Examples (excluding the grease compositions of Comparative Examples <NUM>, <NUM>, and <NUM>) was measured using a running torque tester under conditions shown in Table <NUM> below. Now, the grease compositions made in the Examples and the Comparative Examples were each applied to a test bearing, which was a 62022RUCM (with non-contact seals on both sides), with the balls and the cage removed from the space surrounded by the inner ring, the outer ring, and the seals, into which space the grease composition was filled in so as to be <NUM>% by volume as to the volume of the space.

This test bearing was installed in a test machine and rotated at <NUM>-<NUM> for <NUM> minutes, and the average value of the torque during the final one minute was taken as the bearing running torque. The number of samples was <NUM>, and the average value thereof was used as the evaluation result.

Note that in this evaluation, a running torque of <NUM> mN·m or less is considered to have good low torque properties, and <NUM> mN·m or less is considered to have even better low torque properties.

The average particle size of the thickener contained in the grease compositions prepared in the Examples and the Comparative Examples was measured using a confocal laser microscope (TCS SP08, manufactured by Leica Microsystems). At this time, the configuration of the confocal laser microscope shown in Table <NUM> was employed.

This device has built-in software (Leica Application Suite X (LAS X) Version <NUM>. <NUM>) that can calculate the average particle size of observed objects. Using this software enables calculation of the volume of the thickener for each particle from a three-dimensional image that is acquired, calculation of the diameter of each particle assuming that the shape of each particle is a true sphere, and calculation of the average value of the diameter of each particle as a measured value (average particle size).

The average values of the diameters of the thickeners that were obtained are shown in Table <NUM>.

Claim 1:
A production method of a grease composition, the production method comprising:
providing
a styrene-based polymer,
an amine compound,
an isocyanate compound,
a lubricating oil,
a first solvent that does not dissolve a urea compound that is generated, and
a second solvent that does not dissolve the urea compound that is generated wherein
the content of the styrene-based polymer is <NUM>% by mass or more and <NUM>% by mass or less as to the total amount of the urea compound and the styrene-based polymer;
dissolving or dispersing the amine compound in the first solvent, dissolving or dispersing the isocyanate compound in the second solvent, dissolving or dispersing the styrene-based polymer in one or both of the first solvent and the second solvent, such that a first blended solution containing at least the amine compound and a second blended solution containing at least the isocyanate compound are prepared;
blending the first blended solution and the second blended solution, and carrying out reaction of the amine compound and the isocyanate compound, such that a third blended solution containing the styrene-based polymer and the urea compound is generated; and
adding the lubricating oil after removing the first solvent and the second solvent from the third blended solution.