Grease composition and method for producing the grease composition

Abstract

This grease composition includes a base oil and a thickener, wherein: the thickener contains a urea compound and a styrene-based polymer; the content of the styrene-based polymer is 2 mass% to 30 mass% with respect to the total amount of the urea compound and the styrene-based polymer; and in the thickener, the average diameter of particles having a diameter of at least 0.2 μm is 0.2 μm to 1.0 μm.

Description

[Technical Field]

[0001] This disclosure relates to a grease composition and a method for producing a grease composition. This application claims priority under the international patent application PCT / JP2021 / 027389 filed on 21 July 2021, and incorporates all the provisions contained in the said international patent application. [Background technology]

[0002] Grease compositions are used to lubricate sliding parts such as rolling bearings and gears. Patent documents 1 to 7 describe grease compositions. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2015-193858 [Patent Document 2] Japanese Patent Publication No. 2013-227438 [Patent Document 3] Japanese Patent Publication No. 2012-177105 [Patent Document 4] Japanese Patent Publication No. 2007-297422 [Patent Document 5] U.S. Patent No. 5207935 [Patent Document 6] Japanese Patent Publication No. 2002-327188 [Patent Document 7] International Publication No. 2019 / 017227 [Overview of the project] [Problems that the invention aims to solve]

[0004] Grease compositions used for lubricating rolling bearings, gears, and the like require good oil retention to ensure proper lubrication. Furthermore, to meet the needs for energy saving and increased efficiency in rolling bearings, gears, and the like, there is a demand for grease compositions that can reduce torque. In other words, there is a need for a grease composition that, when used in rolling bearings, gears, and the like, has good oil retention properties while also ensuring low torque. [Means for solving the problem]

[0005] A grease composition relating to one aspect of this disclosure is: It contains a base oil and a thickener. The above thickener comprises a urea compound and a styrene polymer. The content of the above-mentioned styrene polymer is 2% by mass or more and 30% by mass or less relative to the total amount of the above-mentioned urea compound and the above-mentioned styrene polymer. The above-mentioned thickener has an average diameter of 0.2 μm or larger particles that is between 0.2 μm and 1.0 μm.

[0006] A method for producing a grease composition according to another aspect of the present disclosure is: Styrene-based polymers and Amine compounds and, Isocyanate compounds and, Lubricant and A first solvent that does not dissolve the generated urea compound, Prepare a second solvent that does not dissolve the generated urea compound, The above amine compound is dissolved or dispersed in the first solvent, the above isocyanate compound is dissolved or dispersed in the second solvent, and the above styrene polymer is dissolved or dispersed in one or both of the first and second solvents to prepare a first mixture containing at least the above amine compound and a second mixture containing at least the above isocyanate compound. The first mixture and the second mixture are mixed, and the amine compound and the isocyanate compound are reacted to produce a third mixture containing the styrene polymer and the urea compound. After removing the first solvent and the second solvent from the above-mentioned third mixed solution, the above-mentioned lubricating oil is added.

[0007] A method for manufacturing a grease composition according to another aspect of the present disclosure is as follows. A styrene-based polymer, An amine compound, An isocyanate compound, A first lubricating oil, A second lubricating oil, are prepared, The amine compound is dissolved or dispersed in the first lubricating oil, the isocyanate compound is dissolved or dispersed in the second lubricating oil, and the styrene-based polymer is dissolved or dispersed in one or both of the first lubricating oil and the second lubricating oil to prepare a fourth mixed solution containing at least the amine compound and a fifth mixed solution containing at least the isocyanate compound. The fourth mixed solution and the fifth mixed solution are mixed to react the amine compound and the isocyanate compound.

Advantages of the Invention

[0008] The grease composition of the present disclosure has excellent oil retention. When the grease composition of the present disclosure is used in rolling bearings, gears, etc., low torque characteristics can be ensured. According to the method for manufacturing the grease composition of the present disclosure, the grease composition of the present disclosure can be preferably manufactured.

Brief Description of the Drawings

[0009] [Figure 1] It is a configuration diagram schematically showing an example of a dual pinion type electric power steering device in which a grease composition is enclosed. [Figure 2] It is a cross-sectional view taken along line A-A of FIG. 1. [Figure 3] It is a cross-sectional view taken along line B-B of FIG. 1. [Figure 4] It is a configuration diagram schematically showing an example of a column type electric power steering device in which a grease composition is enclosed. [Figure 5] This is a cross-sectional view AA in Figure 4. [Figure 6] This is a cross-sectional view of a rolling bearing containing a grease composition. [Figure 7] This is a process diagram illustrating method A1 for manufacturing a grease composition. [Figure 8] This is a process diagram illustrating method A2 for manufacturing a grease composition. [Figure 9] This is a process diagram illustrating method A3 for manufacturing a grease composition. [Figure 10] This is a process diagram illustrating method B1 for manufacturing the grease composition. [Figure 11] This is a process diagram illustrating method B2 for manufacturing the grease composition. [Figure 12] This is a process diagram illustrating method B3 for manufacturing the grease composition. [Modes for carrying out the invention]

[0010] <Summary of Embodiments of the Invention Disclosed> The embodiments of the invention disclosed herein are outlined below. (1) A grease composition according to one embodiment of the present disclosure comprises a base oil and a thickener, The above thickener comprises a urea compound and a styrene polymer. The content of the above-mentioned styrene polymer is 2% by mass or more and 30% by mass or less relative to the total amount of the above-mentioned urea compound and the above-mentioned styrene polymer. The above-mentioned thickener has an average diameter of 0.2 μm or larger particles that is between 0.2 μm and 1.0 μm.

[0011] The above grease composition contains a urea compound and a predetermined amount of styrene polymer as thickeners, and the average diameter of particles with a diameter of 0.2 μm or more is between 0.2 μm and 1.0 μm. In other words, the above grease composition does not contain coarse thickener particles that tend to occur when the above urea compound is contained alone. Therefore, the above grease composition has good oil retention. In other words, the above grease composition has good oil retention properties. Furthermore, the above grease composition can operate rolling bearings, gears, etc. with low torque. In other words, the above grease composition has good low torque properties.

[0012] On the other hand, the aforementioned Patent Documents 1 to 7 do not describe how good oil retention and good low torque properties can be achieved simultaneously by using a thickening agent that contains a urea compound and a predetermined amount of styrene-based polymer, and by setting the average diameter of the particles of the thickening agent with a diameter of 0.2 μm or more to 1.0 μm.

[0013] (2) In the grease composition of (1) above, the content of the styrene polymer may be 2% by mass or more and 9% by mass or less with respect to the total amount of the urea compound and the styrene polymer.

[0014] (3) In the grease composition of (1) or (2) above, the urea compound is preferably a diurea. In this case, the grease composition is less likely to deteriorate even when used at high temperatures. In other words, the grease composition has good heat resistance.

[0015] (4) In the grease composition described in any of (1) to (3) above, the base oil is preferably poly-α-olephon. In this case, the grease composition exhibits excellent fluidity at low temperatures. In other words, the grease composition has good low-temperature fluidity. Furthermore, it is less likely to degrade components surrounding rolling surfaces that require lubrication, such as rolling bearings and gears, including rubber and resin components. In other words, the grease composition has low corrosiveness towards rubber and resin components.

[0016] (5) In the grease composition described in any of (1) to (4) above, the content of the thickener is preferably 10% by mass or more and 40% by mass or less with respect to the total amount of the base oil and the thickener. In this case, the grease composition has even better low-torque properties.

[0017] (6) In a method for producing a grease composition according to one embodiment of the present disclosure, Styrene-based polymers and Amine compounds and, Isocyanate compounds and, Lubricant and A first solvent that does not dissolve the generated urea compound, Prepare a second solvent that does not dissolve the generated urea compound, The above amine compound and the above styrene polymer are dissolved or dispersed in the above first solvent to prepare the first mixture. The above isocyanate compound and the above styrene polymer are dissolved or dispersed in the second solvent to prepare a second mixture. The first mixture and the second mixture are mixed, and the amine compound and the isocyanate compound are reacted to produce a third mixture containing the styrene polymer and the urea compound. After removing the first solvent and the second solvent from the third mixture, the lubricating oil is added.

[0018] (7) In a method for producing a grease composition according to another embodiment of the present disclosure, Styrene-based polymers and Amine compounds and, Isocyanate compounds and, Lubricant and A first solvent that does not dissolve the generated urea compound, Prepare a second solvent that does not dissolve the generated urea compound, The above amine compound is dissolved or dispersed in the above first solvent to prepare the first mixture. The above isocyanate compound and the above styrene polymer are dissolved or dispersed in the second solvent to prepare a second mixture. The first mixture and the second mixture are mixed, and the amine compound and the isocyanate compound are reacted to produce a third mixture containing the styrene polymer and the urea compound. After removing the first solvent and the second solvent from the third mixture, the lubricating oil is added.

[0019] (8) In a method for producing a grease composition according to another embodiment of the present disclosure, Styrene-based polymers and Amine compounds and, Isocyanate compounds and, Lubricant and A first solvent that does not dissolve the generated urea compound, Prepare a second solvent that does not dissolve the generated urea compound, The above amine compound and the above styrene polymer are dissolved or dispersed in the above first solvent to prepare the first mixture. The above isocyanate compound is dissolved or dispersed in the above second solvent to prepare a second mixture. The first mixture and the second mixture are mixed, and the amine compound and the isocyanate compound are reacted to produce a third mixture containing the styrene polymer and the urea compound. After removing the first solvent and the second solvent from the third mixture, the lubricating oil is added.

[0020] (9) In a method for producing a grease composition according to another embodiment of the present disclosure, Styrene-based polymers and Amine compounds and, Isocyanate compounds and, First lubricant and A second lubricant, Prepare, The above amine compound and the above styrene polymer are dissolved or dispersed in the above first lubricating oil to prepare a fourth mixture. The above isocyanate compound and the above styrene polymer are dissolved or dispersed in the above second lubricating oil to prepare a fifth mixture. The fourth mixture and the fifth mixture are mixed to react the amine compound with the isocyanate compound.

[0021] (10) In a method for producing a grease composition according to another embodiment of the present disclosure, Styrene-based polymers and Amine compounds and, Isocyanate compounds and, First lubricant and A second lubricant, Prepare, The above amine compound is dissolved or dispersed in the above first lubricating oil to prepare a fourth mixture. The above isocyanate compound and the above styrene polymer are dissolved or dispersed in the above second lubricating oil to prepare a fifth mixture. The fourth mixture and the fifth mixture are mixed to react the amine compound with the isocyanate compound.

[0022] (11) In a method for producing a grease composition according to another embodiment of the present disclosure, Styrene-based polymers and Amine compounds and, Isocyanate compounds and, First lubricant and A second lubricant, Prepare, The above amine compound and the above styrene polymer are dissolved or dispersed in the above first lubricating oil to prepare a fourth mixture. The above isocyanate compound is dissolved or dispersed in the above second lubricating oil to prepare a fifth mixture. The fourth mixture and the fifth mixture are mixed to react the amine compound with the isocyanate compound.

[0023] According to the manufacturing methods described in (6) to (11), the grease composition according to the embodiment of this disclosure can be suitably manufactured.

[0024] <Details of Embodiments of the Invention Disclosed> Embodiments of the invention described herein will be described below. In this disclosure, the embodiments of the invention should be considered in all respects to be illustrative and not restrictive. The scope of the invention is indicated by the claims and is intended to include all modifications in the sense and scope of equivalence to the claims.

[0025] First, an apparatus in which the grease composition of this disclosure is used will be described, and then embodiments relating to the grease composition of this disclosure will be described. The grease composition of this disclosure is used, for example, in dual-pinion type electric power steering devices, column type electric power steering devices, rolling bearings, and the like.

[0026] Dual-pinion type electric power steering system Figure 1 is a schematic diagram showing an example of a dual-pinion type electric power steering system 1, including a steering gear unit 3. Figure 2 is a cross-sectional view AA of Figure 1, showing a part of the steering gear device 3. In Figure 2, the lower part of the drawing corresponds to the vertical downward side when mounted in the vehicle. Figure 3 is a cross-sectional view of BB in Figure 1, showing a part of the steering gear device 3. In Figure 3, the lower part of the drawing corresponds to the vertical lower side when mounted in the vehicle.

[0027] The dual-pinion type electric power steering system 1 comprises a steering wheel 10, a steering shaft 2, a first pinion shaft 32, a rack shaft 31, a housing 33, two rack bushings 30 and 34, two bearings 35 and 36, a first rack guide mechanism 39, and a steering assist device 5. The steering assist device 5 comprises a controller 50, a torque sensor 51, an electric motor 52, a reduction mechanism 53, a second pinion shaft 54, two bearings 55 and 56, a worm housing 57, and a second rack guide mechanism 59. The reduction mechanism 53 comprises a worm 531 and a worm wheel 532.

[0028] A driver operating a vehicle equipped with this dual-pinion type electric power steering system 1 steers by rotating the steering wheel 10. The steering shaft 2 comprises a column shaft 21, a first universal joint 23, an intermediate shaft 22, and a second universal joint 24. The first universal joint 23 comprises a first yoke (not shown), a plurality of first rolling elements (not shown), a first cross shaft (not shown), a plurality of second rolling elements (not shown), and a second yoke (not shown). The second universal joint 24 comprises a third yoke (not shown), a plurality of third rolling elements (not shown), a second cross shaft (not shown), a plurality of fourth rolling elements (not shown), and a fourth yoke (not shown).

[0029] The column shaft 21 has a steering wheel 10 fixed to one end in the extending direction. The column shaft 21 has a first yoke of a first universal joint 23 fixed to the other end in the extending direction. The column shaft 21 is rotatable about a central axis in the extending direction. The first yoke is pivotably fitted to a first pair of trunnions on the same central axis of the first cross shaft via a plurality of first rolling elements. The second yoke is pivotably fitted to a second pair of trunnions on the same central axis of the first cross shaft via a plurality of second rolling elements. The central axes of the first pair of trunnions and the central axes of the second pair of trunnions intersect at a 90-degree angle.

[0030] The second yoke of the first universal joint 23 fixes one end of the intermediate shaft 22 in the extending direction. The intermediate shaft 22 fixes the third yoke of the second universal joint 24 to the other end in the extending direction. The third yoke is pivotably fitted to a third pair of trunnions on the same central axis of the second cross shaft via a plurality of third rolling elements. The fourth yoke is pivotably fitted to a fourth pair of trunnions on the same central axis of the second cross shaft via a plurality of fourth rolling elements. The central axes of the third pair of trunnions and the central axes of the fourth pair of trunnions intersect at a 90-degree angle. The fourth yoke of the second universal joint 24 fixes one end of the first pinion shaft 32 in the extending direction. As a result, when the driver rotates the steering wheel 10, the column shaft 21 rotates around its central axis in the direction of extension, the intermediate shaft 22 also rotates around its central axis in the direction of extension, and the first pinion shaft 32 also rotates around its central axis in the direction of extension.

[0031] In the dual-pinion type electric power steering device 1, the first pinion shaft 32, the rack shaft 31, the housing 33, the two rack bushings 30 and 34, the first bearing 35, the second bearing 36, the first rack guide mechanism 39, the electric motor 52, the reduction mechanism 53, the second pinion shaft 54, the third bearing 55, the fourth bearing 56, the worm housing 57, and the second rack guide mechanism 59 constitute the steering gear device 3 as a rack and pinion type steering device. In Figure 1, the housing 33 is represented by a dashed line (two-dotted line), and its interior is illustrated.

[0032] The first pinion shaft 32 extends vertically from the top to the bottom of the automobile. The first pinion shaft 32 has a serrated portion 324, a first shaft portion 322, a first pinion tooth portion 320, and a first boss portion 323 along its extending direction from one end to the other. Serrations are formed on the serrated portion 324. The serrations on the serrated portion 324 are used to fix the fourth yoke of the second universal joint 24. The first shaft portion 322 is cylindrical in shape. The first pinion tooth portion 320 has first pinion teeth 321 formed on its entire circumferential surface. The extending direction of the first pinion teeth 321 is at an angle that is not 90 degrees with respect to the extending direction of the central axis of the first pinion shaft 32. The first boss portion 323 is cylindrical in shape.

[0033] The housing 33 has a first opening 332 on the steering wheel 10 side, and is sealed on the opposite side of the first opening 332. The first pinion shaft 32 is housed inside the housing 33. The first pinion shaft 32 is rotatably supported by two bearings 35, 36 relative to the housing 33. The first bearing 35 is a ball bearing. The first bearing 35 includes an inner ring, an outer ring, and balls, with the inner ring fixed to the first shaft portion 322 and the outer ring fixed to the housing 33, and the balls rolling between the inner and outer rings. The second bearing 36 is a roller bearing. The second bearing 36 includes rollers and an outer ring, with the outer ring fixed to the housing 33, and the rollers rolling between the outer circumferential surface of the first boss portion 323 and the outer ring.

[0034] With the first pinion shaft 32, the first bearing 35, and the second bearing 36 inserted into the housing 33, the first opening 332 of the housing is fixed with a cover 37 through which the first pinion shaft 32 passes. A seal is fixed to the cover 37 and is slidable on the outer circumferential surface 322b of the first shaft portion 322 of the first pinion shaft 32. A cover member 38 is further fixed to the housing 33. The cover member 38 covers a portion of the first shaft portion 322 of the first pinion shaft 32 from the radial outside.

[0035] The rack shaft 31 comprises a first cylindrical portion 316, a first rack tooth portion 310, a second cylindrical portion 317, a second rack tooth portion 314, and a third cylindrical portion 318, extending from one end to the other in the direction of extension. The first rack tooth portion 310 has first rack teeth 311 formed on a part of its circumferential direction, and the other part is a cylindrical surface 312 with the direction of extension of the rack shaft 31 as its central axis. The second rack tooth portion 314 has second rack teeth 315 formed on a part of its circumferential direction, and the other part is a cylindrical surface 313 with the direction of extension of the rack shaft 31 as its central axis. The outer circumferential surfaces of the first cylindrical portion 316, the second cylindrical portion 317, and the third cylindrical portion 318 are each cylindrical surfaces with the direction of extension of the rack shaft 31 as their central axis. The extending direction of the first rack tooth 311 is at an angle that is not 90 degrees with respect to the extending direction of the rack axis. The extending direction of the second rack tooth 315 is at an angle that is not 90 degrees with respect to the extending direction of the rack axis 31. If the angle of the first rack tooth 311 with respect to the extending direction of the rack axis 31 is X, then the angle of the second rack tooth 315 with respect to the extending direction of the rack axis 31 is π-X.

[0036] The housing 33 extends in a direction different from the first opening 332 on the steering wheel 10 side and has a second opening 333 at one end in the extending direction and a third opening 334 at the other end. The rack shaft 31 is housed inside the housing 33 along the extending direction of the housing 33. A first cylindrical portion 316 at one end of the rack shaft 31 in the extending direction protrudes from the second opening 333 at one end of the housing 33 in the extending direction. A third cylindrical portion 318 at the other end of the rack shaft 31 in the extending direction protrudes from the third opening 334 at the other end of the housing 33 in the extending direction. The housing 33 has a fourth opening 335. The fourth opening 335 is located on the other end of the housing in the extending direction than the first opening 332. The housing 33 further has a fifth opening 336 and a sixth opening 337. The fifth opening 336 is located at approximately the same position as the first opening 332 in the extending direction of the housing 33, in the radial direction with the extending direction of the housing 33 as its central axis, and perpendicular to the first opening 332. The sixth opening 337 is located at approximately the same position as the fourth opening 335 in the extending direction of the housing 33, in the radial direction with the extending direction of the housing 33 as its central axis, and perpendicular to the fourth opening 335.

[0037] A first rack bush 30 is fixed to one end of the housing 33 in the extending direction. The first rack bush 30 is fixed to the housing 33 adjacent to the second opening 333. The first rack bush 30 is slidable on the outer circumferential surface of the first cylindrical portion 316 of the rack shaft 31. A second rack bush 34 is fixed to the other end of the housing 33 in the extending direction. The second rack bush 34 is fixed to the housing 33 adjacent to the third opening 334. The second rack bush 34 is slidable on the outer circumferential surface of the third cylindrical portion 318 of the rack shaft 31.

[0038] The first pinion teeth 321 formed on the first pinion tooth portion 320 of the first pinion shaft 32 and the first rack teeth 311 formed on the first rack tooth portion 310 of the rack shaft 31 are in rolling and sliding contact via the grease composition G. The first pinion teeth 321 and the first rack teeth 311 are meshed via the grease composition G. When the first pinion shaft 32 rotates relative to the housing 33 about its central axis in its extending direction, the rack shaft 31 moves linearly relative to the housing 33 in the extending direction of the housing 33.

[0039] A first rack guide mechanism 39 is fixed to the housing 33. The first rack guide mechanism 39 is fixed to a fifth opening 336. The fifth opening 336 is located on the cylindrical surface 312 side, which is the other circumferential part of the first rack teeth 310 of the rack shaft 31, at the position where the first pinion shaft 32 engages with the rack shaft 31 in the extending direction of the housing 33.

[0040] The first rack guide mechanism 39 includes a first support yoke 391, a first seat member 392, a first coil spring 393, and a first plug 394. The first seat member 392 is sandwiched between the cylindrical surface 312, which is the other circumferential part of the first rack teeth 310 of the rack shaft 31, and the cylindrical surface of the first support yoke 391. The first seat member 392 is fixed to the first support yoke 391. The first seat member 392 and the cylindrical surface 312, which is the other circumferential part of the first rack teeth 310 of the rack shaft 31, are in sliding contact via a grease composition G. The first plug 394 is fixed to the fifth opening 336 of the housing 33. The first plug 394 is in contact with one end of the first coil spring 393. The first support yoke 391 is in contact with the other end of the first coil spring 393. The first coil spring 393 is shorter than its free length when the first plug 394 is fixed to the fifth opening 336. Thus, the first seat member 392 is pressed against the rack shaft 31 relative to the housing 33.

[0041] The second pinion shaft 54 ​​extends from the upper to the lower side in the vertical direction of the automobile. The second pinion shaft 54 ​​has a fitting portion 544, a second shaft portion 542, a second pinion tooth portion 540, and a second boss portion 543 along its extending direction from one end to the other. The fitting portion 544 is cylindrical in shape. The second shaft portion 542 is cylindrical in shape. The second pinion tooth portion 540 has second pinion teeth 541 formed on its entire circumferential surface. The extending direction of the second pinion teeth 541 is at an angle that is not 90 degrees with respect to the extending direction of the central axis of the second pinion shaft 54. The second boss portion 543 is cylindrical in shape.

[0042] A worm wheel 532 is fitted into a mating portion 544. A worm 531 is fixed to the output shaft 521 of an electric motor 52. The electric motor 52 is fixed to a worm housing 57. The worm housing 57 has a seventh opening 571. The output shaft 521 of the electric motor 52 is positioned in the internal space of the worm housing 57 through the seventh opening 571. The electric motor 52 is fixed to the worm housing 57 so as to close the seventh opening 571 of the worm housing 57.

[0043] The worm 531 is located in the internal space of the worm housing 57. The worm wheel 532 is located in the internal space of the worm housing 57. The worm housing 57 has an eighth opening 572 located vertically upward, and the assembly of the second pinion shaft 54 ​​and the worm wheel 532 is inserted into the internal space of the worm housing 57 through the eighth opening 572. The eighth opening is closed by a cover 58. The worm housing 57 has a ninth opening 573 on the opposite side of the eighth opening 572. Part of the second shaft portion 542 of the second pinion shaft 54, the second pinion teeth portion 540, and the second boss portion 543 protrude from the ninth opening 573 of the worm housing 57.

[0044] The worm housing 57 is fixed to the housing 33. The ninth opening 573 of the worm housing 57 and the fourth opening 335 of the housing 33 are in communication, sealing the internal space from the external space.

[0045] The third bearing 55 is a ball bearing. The bearing 55 includes an inner ring, an outer ring, and balls, with the inner ring fixed to the second shaft portion 542 and the outer ring fixed to the worm housing 57, and the balls rolling between the inner and outer rings. The bearing 56 is a roller bearing. The bearing 56 includes rollers and an outer ring, with the outer ring fixed to the housing 33, and the rollers rolling between the outer circumferential surface of the second boss portion 543 and the outer ring.

[0046] The second pinion teeth 541 formed on the second pinion tooth portion 540 of the second pinion shaft 54 ​​and the second rack teeth 315 formed on the second rack tooth portion 314 of the rack shaft 31 are in rolling and sliding contact via the grease composition G. The second pinion teeth 541 and the second rack teeth 315 are meshed via the grease composition G. When the second pinion shaft 54 ​​rotates relative to the housing 33 about its central axis in its extending direction, the rack shaft 31 moves linearly relative to the housing 33 in the extending direction of the housing 33.

[0047] The housing 33 has a second rack guide mechanism 59 fixed to it. The second rack guide mechanism 59 is fixed to a sixth opening 337. The sixth opening 337 is located on the cylindrical surface 313 side of the second rack teeth 314 of the rack shaft 31, at the position where the second pinion shaft 54 ​​engages with the rack shaft 31 in the extending direction of the housing 33.

[0048] The second rack guide mechanism 59 includes a second support yoke 591, a second seat member 592, a second coil spring 593, and a second plug 594. The second seat member 592 is sandwiched between the cylindrical surface 313, which is the other circumferential part of the second rack teeth 314 of the rack shaft 31, and the cylindrical surface of the second support yoke 591. The second seat member 592 is fixed to the second support yoke 591. The second seat member 592 and the cylindrical surface 313, which is the other circumferential part of the second rack teeth 314 of the rack shaft 31, are in sliding contact via a grease composition G. The second plug 594 is fixed to the sixth opening 337 of the housing 33. The second plug 594 is in contact with one end of the second coil spring 593. The second support yoke 591 is in contact with the other end of the second coil spring 593. The second coil spring 593 is shorter than its free length when the second plug 594 is fixed to the sixth opening 337. Thus, the second seat member 592 is pressed against the rack shaft 31 relative to the housing 33.

[0049] The torque sensor 51 detects the steering torque applied by the driver to the steering wheel 10 via the column shaft 21. The reduction mechanism 53 is an assembly in which a worm 531, which rotates integrally with the output shaft 521 of the electric motor 52, and a worm wheel 532, which rotates integrally with the second pinion shaft 54, are meshed together. Motor current is supplied to the electric motor 52 from the controller 50. The controller 50 controls the electric motor 52 based on the steering torque and vehicle speed detected by the torque sensor 51, and transmits the rotational force of the output shaft 521 of the electric motor 52, which has been reduced by the reduction mechanism 53, to the second pinion shaft 54. The rotational force of the second pinion shaft 54 ​​is applied as a steering assist force from the second pinion teeth 541 to the second rack teeth 315.

[0050] The housing 33 is fixed to an automobile (not shown) with its extension direction aligned with the width direction of the vehicle. Ball joint sockets 11, 11 are fixed to one end and the other end of the rack shaft 31, respectively, and tie rods 12, 12 connected to these ball joint sockets 11, 11 are connected via knuckle arms 13, 13 to the raceways of rolling bearings that rotatably support a pair of left and right front wheels 14, 14. The rack shaft 31 moves linearly in the extension direction of the housing 33, thereby steering the left and right front wheels 14, 14, which are the steering wheels.

[0051] A grease composition G is sealed inside the housing 33. The grease composition G lubricates the space between the rolling and sliding surfaces of the first pinion teeth 321 and the first rack teeth 311, which come into contact when the first pinion teeth 321 and the first rack teeth 311 mesh with each other. The grease composition G also lubricates the space between the sliding surface of the first seat member 392 and the sliding surface of the cylindrical surface 312, which is the other circumferential part of the first rack teeth portion 310 of the rack shaft 31, which come into contact when the first seat member 392 and the rack shaft 31 are pressed against each other. Grease composition G lubricates the space between the rolling and sliding surfaces of the second pinion teeth 541 and the second rack teeth 315, which come into contact when the second pinion teeth 541 and the second rack teeth 315 mesh with each other. Grease composition G lubricates the space between the sliding surface of the second seat member 592 and the sliding surface of the cylindrical surface 313, which is the other circumferential part of the second rack teeth portion 314 of the rack shaft 31, which come into contact when the second seat member 592 and the rack shaft 31 are pressed against each other.

[0052] The steering gear device 3 configured in this manner has the grease composition of the present disclosure sealed inside as the grease composition G. Since the grease composition of the present disclosure has oil retention properties, the steering gear device 3 has good seizure resistance and wear resistance.

[0053] ≪Column-type electric power steering system≫ Figure 4 is a schematic diagram showing an example of a column-type electric power steering system 601, including a steering gear unit 603. Figure 5 is a cross-sectional view AA of Figure 4, showing a part of the steering gear device 603. In Figure 5, the lower part of the drawing corresponds to the vertical downward side when mounted in the vehicle.

[0054] The column-type electric power steering system 601 comprises a steering wheel 610, a steering shaft 602, a pinion shaft 632, a rack shaft 631, a housing 633, two rack bushings 630 and 634, two bearings 635 and 636, a rack guide mechanism 639, and a steering assist device 4. A driver operating a vehicle equipped with this column-type electric power steering system 601 steers by rotating the steering wheel 610. The steering shaft 602 comprises a column shaft 621, a first universal joint 623, an intermediate shaft 622, and a second universal joint 624. The first universal joint 623 comprises a first yoke (not shown), a plurality of first rolling elements (not shown), a first cross shaft (not shown), a plurality of second rolling elements (not shown), and a second yoke (not shown). The second universal joint 624 comprises a third yoke (not shown), a plurality of third rolling elements (not shown), a second cross shaft (not shown), a plurality of fourth rolling elements (not shown), and a fourth yoke (not shown).

[0055] A steering wheel 610 is fixed to one end of the column shaft 621 in the extending direction. The first yoke of a first universal joint 623 is fixed to the other end of the column shaft 621 in the extending direction. The column shaft 621 is rotatable about its central axis in the extending direction. The first yoke is pivotably fitted to a first pair of trunnions, which lie on the same central axis of the first cross shaft, via a plurality of first rolling elements. The second yoke is pivotably fitted to a second pair of trunnions, which lie on the same central axis of the first cross shaft, via a plurality of second rolling elements. The central axes of the first pair of trunnions and the central axes of the second pair of trunnions intersect at a 90-degree angle.

[0056] The second yoke of the first universal joint 623 fixes one end of the intermediate shaft 622 in the extending direction. The intermediate shaft 622 fixes the third yoke of the second universal joint 624 to the other end in the extending direction. The third yoke is pivotably fitted via a plurality of third rolling elements to a third pair of trunnions that lie on the same central axis of the second cross shaft. The fourth yoke is pivotably fitted via a plurality of fourth rolling elements to a fourth pair of trunnions that lie on the same central axis of the second cross shaft. The central axes of the third pair of trunnions and the central axes of the fourth pair of trunnions intersect at a 90-degree angle. The fourth yoke of the second universal joint 624 fixes one end of the pinion shaft 632 in the extending direction. As a result, when the driver rotates the steering wheel 610, the column shaft 621 rotates around its central axis in the direction of extension, the intermediate shaft 622 also rotates around its central axis in the direction of extension, and the pinion shaft 632 also rotates around its central axis in the direction of extension.

[0057] Of the column-type electric power steering device 601, the pinion shaft 632, rack shaft 631, housing 633, two rack bushings 630 and 634, two bearings 635 and 636, and rack guide mechanism 639 constitute the steering gear device 603 as a rack and pinion type steering device. In Figure 4, the housing 633 is represented by a dashed line (two-dot line), and its interior is illustrated.

[0058] The pinion shaft 632 extends from the top to the bottom in the vertical direction of the automobile. The pinion shaft 632 has a serrated portion 724, a shaft portion 722, a pinion tooth portion 720, and a boss portion 723 along its extending direction from one end to the other. Serrations are formed on the serrated portion 724. The serrations on the serrated portion 724 are used to fix the fourth yoke of the second universal joint 624. The shaft portion 722 is cylindrical in shape. Pinion teeth 721 are formed on the entire circumferential surface of the pinion tooth portion 720. The extending direction of the pinion teeth 721 is at an angle that is not 90 degrees with respect to the extending direction of the central axis of the pinion shaft 632. The boss portion 723 is cylindrical in shape.

[0059] The housing 633 has a first opening 732 on the steering wheel 610 side, and is sealed on the opposite side of the first opening 732. The pinion shaft 632 is housed inside the housing 633. The pinion shaft 632 is rotatably supported by two bearings 635 and 636 relative to the housing 633. Bearing 635 is a ball bearing. Bearing 635 includes an inner ring, an outer ring, and balls, with the inner ring fixed to the shaft portion 722 and the outer ring fixed to the housing 633, and the balls rolling between the inner and outer rings. Bearing 636 is a roller bearing. Bearing 636 includes rollers and an outer ring, with the outer ring fixed to the housing 633, and the rollers rolling between the outer circumferential surface of the boss portion 723 and the outer ring.

[0060] With the pinion shaft 632 and two bearings 635 and 636 inserted into the housing 633, the first opening 732 of the housing is fixed with a cover 637 through which the pinion shaft 632 passes. A seal is fixed to the cover 637 and is slidable on the outer circumferential surface 722b of the shaft portion 722 of the pinion shaft 632. A cover member 638 is further fixed to the housing 633. The cover member 638 covers a portion of the shaft portion 722 of the pinion shaft 632 from the radial outside.

[0061] The rack shaft 631 comprises a first cylindrical portion 716, a rack tooth portion 710, and a second cylindrical portion 717, extending from one end to the other in the direction of extension. The rack tooth portion 710 has rack teeth 711 formed on a part of its circumferential direction, while the other part in the circumferential direction is a cylindrical surface 712 with the direction of extension of the rack shaft 631 as its central axis. The outer circumferential surfaces of the first cylindrical portion 716 and the second cylindrical portion 717 are both cylindrical surfaces with the direction of extension of the rack shaft 631 as their central axis. The direction of extension of the rack teeth 711 is at an angle that is not 90 degrees with respect to the direction of extension of the rack shaft 631.

[0062] The housing 633 extends in a direction different from the first opening 732 on the steering wheel 610 side and has a second opening 733 at one end in the direction of extension and a third opening 734 at the other end. The rack shaft 631 is housed inside the housing 633 along the direction of extension of the housing 633. One end of the rack shaft 631 in the direction of extension protrudes from the second opening 733 at the one end of the housing 633 in the direction of extension. The other end of the rack shaft 631 in the direction of extension protrudes from the third opening 734 at the other end of the housing 633 in the direction of extension.

[0063] A first rack bush 630 is fixed to one end of the housing 633 in the extending direction. The first rack bush 630 is fixed to the housing 633 adjacent to the second opening 733. The first rack bush 630 is slidable on the outer circumferential surface of the first cylindrical portion 716 of the rack shaft 631. A second rack bush 634 is fixed to the other end of the housing 633 in the extending direction. The second rack bush 634 is fixed to the housing 633 adjacent to the third opening 734. The second rack bush 634 is slidable on the outer circumferential surface of the second cylindrical portion 717 of the rack shaft 631.

[0064] The pinion teeth 721 formed on the pinion teeth portion 720 of the pinion shaft 632 and the rack teeth 711 formed on the rack teeth portion 710 of the rack shaft 631 are in rolling and sliding contact via the grease composition G. The pinion teeth 721 and the rack teeth 711 are meshed via the grease composition G. When the pinion shaft 632 rotates relative to the housing 633 about its central axis in the direction of its extension, the rack shaft 631 moves linearly relative to the housing 633 in the direction of its extension.

[0065] The housing 633 is fixed to an automobile (not shown) with its extension direction aligned with the width direction of the vehicle. Ball joint sockets 11, 11 are fixed to one end and the other end of the rack shaft 631, respectively, and tie rods 12, 12 connected to these ball joint sockets 11, 11 are connected via knuckle arms 13, 13 to the raceways of rolling bearings that rotatably support a pair of left and right front wheels 14, 14. The rack shaft 631 moves linearly in the extension direction of the housing 633, thereby steering the left and right front wheels 14, 14, which are the steering wheels.

[0066] The housing 633 has a rack guide mechanism 639 fixed to it. The housing 633 has a fourth opening 736 on the cylindrical surface 712 side, which is the other side in the circumferential direction of the rack teeth 710 of the rack shaft 631, at the position where the pinion shaft 632 engages with the rack shaft 631 in the extending direction.

[0067] The rack guide mechanism 639 includes a support yoke 791, a seat member 792, a coil spring 793, and a plug 794. The seat member 792 is sandwiched between the cylindrical surface 712, which is the other circumferential part of the rack teeth 710 of the rack shaft 631, and the cylindrical surface of the support yoke 791. The seat member 792 is fixed to the support yoke 791. The seat member 792 and the cylindrical surface 712, which is the other circumferential part of the rack teeth 710 of the rack shaft 631, are in sliding contact via a grease composition G. The plug 794 is fixed to the fourth opening 736 of the housing 633. The plug 794 is in contact with one end of the coil spring 793. The support yoke 791 is in contact with the other end of the coil spring 793. The coil spring 793 is shorter than its free length when the plug 794 is fixed to the fourth opening 736. Therefore, the seat member 792 is pressed against the rack shaft 631 relative to the housing 633.

[0068] The steering assist device 4 includes a controller 40, a torque sensor 41 that detects the steering torque applied by the driver to the steering wheel 610, an electric motor 42, and a reduction mechanism 43 that reduces the rotational force of the output shaft 421 of the electric motor 42 and transmits it to the column shaft 621. The reduction mechanism 43 is an assembly in which a worm 431 that rotates integrally with the output shaft 421 of the electric motor 42 and a worm wheel 432 that rotates integrally with the column shaft 621 are meshed together. Motor current is supplied to the electric motor 42 from the controller 40. The controller 40 controls the electric motor 42 based on the steering torque and vehicle speed detected by the torque sensor 41, and the rotational force of the output shaft 421 of the electric motor 42, which has been reduced by the reduction mechanism 43, is applied to the column shaft 621 as a steering assist force.

[0069] A grease composition G is sealed inside the housing 633. The grease composition G lubricates the space between the rolling and sliding surfaces of the pinion teeth 721 and the rack teeth 711, which come into contact when the pinion teeth 721 and rack teeth 711 mesh with each other. The grease composition G lubricates the space between the sliding surface of the seat member 792 and the sliding surface of the cylindrical surface 712, which is the other circumferential part of the rack teeth portion 710 of the rack shaft 631, which come into contact when the seat member 792 and the rack shaft 631 are pressed against each other.

[0070] The steering gear device 603 configured in this manner has the grease composition of the present disclosure sealed inside as the grease composition G. Since the grease composition of the present disclosure ensures oil retention, the steering gear device 603 has good seizure resistance and wear resistance.

[0071] Rolling bearings Figure 6 is a cross-sectional view of a ball bearing 801, which is an example of a rolling bearing. The ball bearing 801 comprises an inner ring 802, an outer ring 803 provided radially outside the inner ring 802, a plurality of rolling elements, balls 804, provided between the inner ring 802 and the outer ring 803, and an annular cage 805 that holds these balls 804. In addition, seals 806 are provided on one axial side and the other side of the ball bearing 801. Furthermore, the annular region 807 between the inner ring 802 and the outer ring 803 is filled with grease composition G.

[0072] The inner ring 802 has an inner raceway surface 821 formed on its outer circumference, on which the ball 804 rolls. The outer ring 803 has an outer raceway surface 831 formed on its inner circumference, on which the ball 804 rolls. Multiple balls 804 are interposed between the inner raceway surface 821 and the outer raceway surface 831, and they roll on these inner and outer raceway surfaces 821 and 831. The grease composition G sealed in region 807 is also present at the contact points between the ball 804 and the inner raceway surface 821 of the inner ring 802, and at the contact points between the ball 804 and the outer raceway surface 831 of the outer ring 803. The grease composition G is sealed in such a way that it occupies 20% to 40% of the volume of the space remaining after removing the ball 804 and the retainer 805 from the space surrounded by the inner ring 802, the outer ring 803, and the seal 806. The seal 806 is an annular member comprising an annular core metal 806a and an elastic member 806b fixed to the core metal 806a, with its radially outer portion fixed to the outer ring 803 and its radially inner portion slidably mounted to the inner ring 802. The seal 806 prevents the sealed grease composition G from leaking to the outside.

[0073] The ball bearing 801 configured in this way is sealed with the grease composition G of the present disclosure. Since the grease composition of the present disclosure ensures oil retention, the ball bearing 801 has good seizure resistance and wear resistance.

[0074] The grease composition of this disclosure can be used by sealing it in the dual-pinion type electric power steering device, column type electric power steering device, rolling bearings, etc.

[0075] Grease Composition A grease composition according to the embodiments of this disclosure comprises a base oil and a thickener, wherein the thickener comprises a urea compound and a styrene polymer.

[0076] (Base oil) Examples of the above-mentioned base oils include poly-α-olefin (PAO), ester oil, polyalkylene glycol, fluorine oil, silicone oil, and ether oil. Among these, poly-α-olefin (PAO) is preferred. This is because the grease composition has good low-temperature fluidity when poly-α-olefin is used. Furthermore, the grease composition has weak aggressiveness towards rubber and resin components.

[0077] Examples of the poly-α-olefins mentioned above include α-olefins such as 1-hexene, 1-octene, 1-nonene, 1-decene, 1-dodecene, and 1-tetradecene, which are oligomerized or polymerized, and further, those which are hydrogenated. As the poly-α-olefins mentioned above, PAO4 to PAO8, which are oligomerized 1-decene, are preferred.

[0078] The kinematic viscosity of the above base oil at 40°C is 20 mm². 2 / s or more 60mm 2 A torque of / s or less is preferable. In this case, the above grease composition is suitable for reducing torque. The kinematic viscosity of the base oil (at 40°C) is 25 mm 2 / s or more 50mm 2 / s or less is preferable. The kinematic viscosity of the base oil mentioned above is a value in accordance with JIS K 2283.

[0079] (Thickener) The thickener described above is a mixture containing a urea compound and a styrene-based polymer. When a grease composition contains a thickener comprising a urea compound and a styrene-based polymer, the grease composition has good oil retention properties and is suitable for ensuring low torque performance.

[0080] [Urea compounds] Examples of the above-mentioned urea compounds include urea compounds such as diurea, triurea, tetraurea, and polyurea (excluding diurea, triurea, and tetraurea), urea-urethane compounds, urethane compounds such as diurethane, or mixtures thereof.

[0081] As the above urea compound, diurea represented by the following structural formula (1) is preferred in that the above grease composition has good heat resistance. R 1 -NHCONH-R 2 -NHCONH-R 3 ...(1) (In formula (1), R1 and R 3 each independently represents an amino residue, and R 2 represents a diisocyanate residue.) The diurea represented by the above structural formula (1) is a reaction product of an amine compound and a diisocyanate compound.

[0082] The above amine compound may be any amine compound known as an amine compound for synthesizing diurea known as a thickener. Examples of the above amine compound include alkylamine, alkylphenylamine, cyclohexylamine, etc. Among these, alkylamine is preferable in that the grease composition has good low torque property and in that the grease composition has good heat resistance.

[0083] The above diisocyanate compound may be any diisocyanate compound known as a diisocyanate compound for synthesizing diurea known as a thickener. Examples of the above diisocyanate compound include 2,4-toluene diisocyanate (2,4-TDI), 2,6-toluene diisocyanate (2,6-TDI), a mixture of 2,4-TDI and 2,6-TDI, 4,4′-diphenylmethane diisocyanate (MDI), etc.

[0084] The content of the above thickener is preferably 10% by mass or more and 40% by mass or less based on the total amount of the above base oil and the above thickener. This is because the grease composition has good low torque property.

[0085] In order to obtain the diurea represented by the above structural formula (1), the above amine compound and the above diisocyanate compound can be reacted under various conditions. The above reaction may be carried out, for example, (a) in a base oil or (b) in a solvent. If carried out in a base oil, the resulting mixture can be used as a grease composition. If carried out in a solvent, the solvent can be removed to obtain powdered diurea, and then the powdered diurea can be mixed with the base oil to obtain a grease composition. The method for producing the above grease composition will be described in detail later.

[0086] [Styrene polymer] The above-mentioned styrene-based polymer is a polymer that contains styrene or a derivative thereof as a monomer component. The styrene-based polymer described above may be a homopolymer of styrene or its derivatives, or it may be a copolymer of a first monomer component selected from styrene and its derivatives with another monomer component. The other monomer component may be styrene or its derivatives, as long as it is different from the first monomer component. Examples of the above copolymers include random copolymers, alternating copolymers, block copolymers, and graft copolymers.

[0087] Examples of the styrene homopolymers mentioned above include atactic polystyrene, isotactic polystyrene, poly-p-methylstyrene, poly-p-ethylstyrene, poly-p-isopropylstyrene, and poly-α-methylstyrene.

[0088] Examples of the copolymers mentioned above include copolymers of a first monomer component selected from styrene and its derivatives with styrene or its derivatives other than the first monomer component. Examples of the copolymers mentioned above include copolymers of the first monomer component and an alkadiene. Examples of alkadienes include butadiene, isoprene, pentadiene, and hexadiene.

[0089] Styrene-isoprene copolymer is preferred as the copolymer. In the above-mentioned styrene-isoprene copolymer, the ratio (molar ratio) of styrene to isoprene should be styrene:isoprene = 1:9 to 9:1. The above copolymer is not limited to copolymers of two monomer components, but may also be a copolymer of three or more monomer components.

[0090] The number-average molecular weight of the above styrene-based polymer is preferably between 10,000 and 500,000, and more preferably between 20,000 and 200,000. The above number-average quantities are measured using gel permeation chromatography.

[0091] Commercially available styrene-based polymers can also be used as the above-mentioned polymers. Examples of commercially available products include Lubrizol® 7306 (manufactured by Lubrizol Nippon Co., Ltd.), 7308, 7460, Infineum® SV140 (manufactured by Infineum Inc.), 150, 160, Septon® 1001 (manufactured by Kuraray Inc.), 1020, and others.

[0092] The styrene polymer content is 2% by mass or more and 30% by mass or less relative to the total amount of the urea compound and the styrene polymer. When the styrene-based polymer content is less than 2% by mass, the grease composition does not have good oil retention or good low torque properties. On the other hand, even when it exceeds 30% by mass, the oil retention of the grease composition does not improve much.

[0093] From the viewpoint of ensuring good oil retention and good low torque properties, the content of the styrene-based polymer is preferably 2% by mass or more and 20% by mass or less, and more preferably 2% by mass or more and 9% by mass or less, relative to the total amount of the urea compound and the styrene-based polymer.

[0094] In the above grease composition, the thickener has an average diameter of particles with a diameter of 0.2 μm or more that is between 0.2 μm and 1.0 μm. The average diameter of the thickener is calculated by assuming the shape of the thickener particles is a perfect sphere and determining the average diameter from the volume of the particles. The particle diameter of the thickening agent described above is measured using a confocal laser microscope with a laser beam of wavelength 488 nm as the excitation light. In observation of thickeners using a confocal laser microscope, particles with a diameter of less than 0.2 μm cannot be observed due to the resolution of the confocal laser microscope. Therefore, the grease composition of this disclosure specifies the average diameter of the thickener particles with a diameter of 0.2 μm or more as the average value of the thickener diameter. This does not mean that the above-mentioned grease composition does not contain thickening agent particles with a diameter of less than 0.2 μm.

[0095] When the above grease composition is irradiated with laser light of a wavelength of 488 nm, the urea compound constituting the thickener emits fluorescence, and the urea compound is observed as a fluorescence image. Furthermore, in the above grease composition, the styrene-based polymer exists in an intertwined state with the urea compound. Therefore, in the grease composition of this disclosure, the fluorescence image of the urea compound observed with a confocal laser microscope is considered to be the fluorescence image of the thickening agent particles. Furthermore, in the above observation, the volume of the thickener particles is measured, the shape of the thickener particles is assumed to be a perfect sphere, the diameter of the thickener particles is calculated from the measured volume, and the average value is calculated. The average value of the above diameter can be calculated using commercially available analysis software.

[0096] The above thickener achieves both oil retention and improved low-torque performance by setting the average diameter of particles with a diameter of 0.2 μm or more to 0.2 μm or more and 1.0 μm or less. If the average diameter exceeds 1.0 μm, oil retention and low torque performance will decrease. On the other hand, as mentioned above, since no thickening agent particles with a diameter of less than 0.2 μm could be observed, the lower limit of the average diameter is 0.2 μm.

[0097] The above-mentioned grease composition may contain additives to the extent that they do not impair the effects of the present invention. Examples of such additives include antioxidants, rust inhibitors, extreme pressure agents, wear inhibitors, dyes, color stabilizers, thickeners, structural stabilizers, metal deactivators, viscosity index improvers, and the like. If the above grease composition contains additives, it is preferable that the total content of the additives in the grease composition be 10% by mass or less relative to the total mass of the base oil and the thickener.

[0098] As described above, the grease composition of this disclosure can be suitably used, for example, as a grease composition to be sealed in gears such as electric power steering gears in automobiles, or in rolling bearings.

[0099] ≪Method for producing grease composition≫ As a method for producing the grease composition of this disclosure, one can employ (a) a method in which a urea compound is synthesized in a solvent and then the obtained urea compound is mixed with a base oil (hereinafter also referred to as production method A), or (b) a method in which a urea compound is synthesized in a base oil (hereinafter also referred to as production method B). The above-mentioned urea compound can be synthesized by mixing an amine compound and an isocyanate compound in a predetermined molar ratio and reacting the amine compound with the isocyanate compound. Below, the method for producing the above-mentioned grease composition will be explained using the case where a diisocyanate compound is used as the isocyanate compound and diurea is synthesized as the urea compound as an example.

[0100] (Manufacturing method A) Examples of specific embodiments of manufacturing method A include manufacturing methods A1 to A3.

[0101] [Manufacturing method A1] Figure 7 is a process diagram illustrating method A1 for manufacturing the grease composition. (1) In manufacturing method A1, first, predetermined amounts of amine compound, diisocyanate compound, styrene polymer, solvent A, and solvent B are prepared. Specific examples of amine compounds, diisocyanate compounds, and styrene polymers are as described above.

[0102] Solvents A and B should each have a lower boiling point than the prepared styrene-based polymer and be able to dissolve the prepared styrene-based polymer. Specific examples of solvents A and B include, for example, toluene, hexane, ethyl acetate, tetrahydrofuran, p-xylene, m-xylene, o-xylene, and methyl acetate. It is preferable to avoid using substances that react with isocyanate groups, such as substances having amine groups or hydroxyl groups, or substances that react with amine groups, as solvents A and B. The solvents A and B described above are preferably those with a lower viscosity than the prepared styrene-based polymer. In this disclosure, the viscosity of the solvent and the styrene-based polymer is measured using a Cannon-Fenske viscometer according to the method of JIS Z8803:2011.

[0103] Solvent A and solvent B may be the same or different, but it is preferable that they be the same. In subsequent steps, when mixture A containing solvent A and mixture B containing solvent B are mixed, the two mixtures mix reliably, making it suitable for promoting the reaction between amine compounds and diisocyanate compounds. Furthermore, when solvents A and B are removed in subsequent steps, the selection of removal methods and conditions becomes easier.

[0104] (2) Next, a portion of the styrene polymer and an amine compound are added to solvent A to obtain a mixture A (S111). At this time, the timing of adding the styrene polymer and amine compound to solvent A is not particularly limited. (a) A solution may be prepared by dissolving a styrene polymer in solvent A, and then an amine compound may be dissolved or dispersed in the resulting solution to obtain a mixture A. (b) A mixture may be prepared by dissolving or dispersing an amine compound in solvent A, and then a styrene polymer may be dissolved in the resulting mixture to obtain mixture A. (c) The amine compound and the styrene polymer may be added to solvent A simultaneously, and then all components may be mixed to obtain mixture A. In this case, the amount of the amine compound should be, for example, 5% by mass or more and 60% by mass or less relative to 100% by mass of solvent A. Furthermore, the amount of styrene polymer may be, for example, 0.3% by mass or more and 30% by mass or less relative to 100% by mass of solvent A.

[0105] (3) Separately from step (2) above, the remaining styrene polymer and diisocyanate compound are added to solvent B to obtain mixed solution B (S112). At this time, the timing of adding the styrene polymer and diisocyanate compound to solvent B is not particularly limited. (a) A solution may be prepared by dissolving a styrene polymer in solvent B, and then a diisocyanate compound may be dissolved or dispersed in the resulting solution to obtain a mixed solution B. (b) A mixture may be prepared by dissolving or dispersing a diisocyanate compound in solvent B, and then a styrene polymer may be dissolved in the resulting mixture to obtain mixture B. (c) The diisocyanate compound and the styrene polymer may be added to solvent B simultaneously, and then all components may be mixed to obtain mixture B. In this case, the amount of the diisocyanate compound should be, for example, 5% by mass or more and 60% by mass or less relative to 100% by mass of solvent B. Furthermore, the amount of styrene-based polymer should be, for example, 0.3% by mass or less per 100% by mass of solvent B, or 30% by mass or less.

[0106] (4) Next, mixture A and mixture B are mixed to react the amine compound with the diisocyanate compound to synthesize diurea (S113). Here, you can either stir mixture A while adding mixture B dropwise to mix the two, or stir mixture B while adding mixture A dropwise to mix the two. The mixing of mixture A and mixture B may be carried out at room temperature or under heating. If the process is carried out under heating, the heating temperature should be, for example, between 40°C and 110°C.

[0107] The mixture of mixture A and mixture B may be mixed in such a ratio of 2 to 2.2 moles of amine compound to 1 mole of diisocyanate compound. The reaction time between the amine compound and the diisocyanate compound is not particularly limited; any time sufficient for the reaction to proceed adequately is acceptable. Specifically, for example, a reaction time of 0.2 hours or more and 5 hours or less is appropriate.

[0108] In steps (2) to (4) above, the mixing of the amine compound, diisocyanate compound, and styrene polymer into their respective solvents, as well as the mixing of mixture A and mixture B, can be carried out using, for example, a mechanical stirrer or a magnetic stirrer. Among these, the method using a mechanical stirrer is preferred because it makes it easier to uniformly mix each component.

[0109] By going through steps (1) to (4) as described above, a mixture containing diurea, a styrene-based polymer, solvent A, and solvent B can be obtained.

[0110] (5) Remove solvent A and solvent B from the mixture obtained in step (4) above (S114). The method for removing solvents A and B is not particularly limited; they can be vaporized at room temperature, or by heating, reducing pressure, stirring, etc., as needed. The specific method can be appropriately selected depending on the types of solvents A and B, and the following methods are examples. For example, one method involves leaving the above mixture at room temperature and atmospheric pressure to vaporize solvent A and solvent B. Another method involves heating the mixture under atmospheric pressure at a temperature lower than the boiling points of solvents A and B to vaporize them. In this case, examples of heating conditions include heating under atmospheric pressure in a constant temperature bath at 40°C for 5 to 10 hours. These methods can be combined.

[0111] (6) Next, the mixture remaining after removing solvent A and solvent B is washed (S115). This washing process removes any unreacted amine compounds or diisocyanate compounds that remain in the mixture. Here are some specific examples of cleaning methods, such as the following: First, the mixture after removing solvents A and B is mixed with water, filtered through a membrane filter, and the residue is collected. Then, the residue is heated at a temperature lower than the boiling point of water and lower than the boiling point of the styrene polymer to vaporize the water adhering to the residue, and the water is removed from the residue. Examples of heating conditions include heating in a high-temperature bath at 80°C under atmospheric pressure for 5 to 10 hours.

[0112] (7) The washed mixture is recovered to obtain mixture C containing diurea and a styrene polymer (S116). The resulting mixture C may be subjected to diurea pulverization as needed. Pulverization can be performed to finely and homogenize the thickener. When performing the above-mentioned grinding process, it is preferable to use a small grinder (for example, Lab Millser, manufactured by Osaka Chemical Co., Ltd.) because it can be carried out with simple equipment and at low cost.

[0113] (8) Next, the base oil is added to mixture C containing diurea and styrene polymer, and the two are mixed (S117). Specific examples of the above-mentioned base oils are as described above.

[0114] Here, the base oil may be stirred while the mixture C is added dropwise to mix the two, or the mixture C may be stirred while the base oil is added dropwise to mix the two. The mixing of the above mixture C and the above base oil is preferably carried out under heating. In this case, the heating temperature should be, for example, 130°C to 180°C. The mixing time between the above mixture C and the above base oil is not particularly limited; for example, it may be between 0.5 hours and 2 hours.

[0115] The method for mixing the above mixture C with the base oil is not particularly limited as long as the two are mixed uniformly, and examples include using a mechanical stirrer or a magnetic stirrer. Among these, the method using a mechanical stirrer is preferred because it makes it easier to mix the two uniformly.

[0116] The above-mentioned grease composition can be manufactured through this process.

[0117] [Manufacturing method A2] Figure 8 is a process diagram illustrating method A2 for manufacturing the grease composition. (1) In manufacturing method A2, first, predetermined amounts of the amine compound, diisocyanate compound, styrene polymer, solvent A, and solvent B are prepared. Specific examples and preferred examples of amine compounds, diisocyanate compounds, and styrene-based polymers are as described above.

[0118] Specific examples, preferred examples, and examples to avoid of solvent A and solvent B are the same as in manufacturing method A1. Solvent A and solvent B may be the same or different, but it is preferable that they be the same.

[0119] (2) Next, an amine compound is added to solvent A to obtain a mixed solution A' (S121). In this case, the amount of the amine compound should be, for example, 5% to 60% by mass relative to 100% by mass of solvent A.

[0120] (3) Separately from step (2) above, a styrene polymer and a diisocyanate compound are added to solvent B to obtain a mixture B (S122). At this time, the timing of adding the styrene polymer and diisocyanate compound to solvent B is not particularly limited. (a) A solution may be prepared by dissolving a styrene polymer in solvent B, and then a diisocyanate compound may be dissolved or dispersed in the resulting solution to obtain a mixed solution B. (b) A mixture may be prepared by dissolving or dispersing a diisocyanate compound in solvent B, and then a styrene polymer may be dissolved in the resulting mixture to obtain mixture B. (c) The diisocyanate compound and the styrene polymer may be added to solvent B simultaneously, and then all components may be mixed to obtain mixture B. In this case, the amount of the diisocyanate compound should be, for example, 5% to 60% by mass relative to 100% by mass of solvent B. Furthermore, the amount of styrene polymer may be, for example, 0.3% to 30% by mass relative to 100% by mass of solvent B.

[0121] (4) Next, mixture A' and mixture B are mixed to react the amine compound with the diisocyanate compound to synthesize diurea (S123). This process can be carried out in the same manner as step (4) of manufacturing method A1, except that mixture A is replaced with mixture A'.

[0122] In steps (2) to (4) above, the mixing of the amine compound, diisocyanate compound, and styrene polymer into their respective solvents, as well as the mixing of mixture A' and mixture B, can be carried out using, for example, a mechanical stirrer or a magnetic stirrer. Among these, the method using a mechanical stirrer is preferred because it facilitates the uniform mixing of each component.

[0123] By going through steps (1) to (4) as described above, a mixture containing diurea, a styrene-based polymer, solvent A, and solvent B can be obtained.

[0124] (5) Remove solvent A and solvent B from the mixture obtained in step (4) above (S124). This process can be carried out in the same manner as in step (5) of manufacturing method A1.

[0125] (6) Next, the mixture remaining after removing solvent A and solvent B is washed (S125). This washing process removes any unreacted amine compounds or diisocyanate compounds that remain in the mixture. This process can be carried out in the same manner as step (6) of manufacturing method A1.

[0126] (7) The washed mixture is collected to obtain mixture C containing diurea and a styrene polymer (S126). The resulting mixture C may be subjected to diurea pulverization as needed. Pulverization can be performed to finely and homogenize the thickener. When performing the above-mentioned grinding process, it is preferable to use a small grinder (for example, Lab Millser, manufactured by Osaka Chemical Co., Ltd.) because it can be carried out with simple equipment and at low cost.

[0127] (8) Next, the base oil is added to mixture C containing diurea and styrene polymer, and the two are mixed (S127). Specific examples of the above-mentioned base oils are as described above. The mixing of mixture C with the base oil may be carried out in the same manner as in step (8) of manufacturing method A1.

[0128] The above-mentioned grease composition can also be manufactured by going through such a process.

[0129] [Manufacturing method A3] Figure 9 is a process diagram illustrating method A3 for manufacturing the grease composition. (1) In manufacturing method A3, first, predetermined amounts of the amine compound, diisocyanate compound, styrene polymer, solvent A, and solvent B are prepared. Specific examples and preferred examples of amine compounds, diisocyanate compounds, and styrene-based polymers are as described above.

[0130] Specific examples, preferred examples, and examples to avoid of solvent A and solvent B are the same as in manufacturing method A1. Solvent A and solvent B may be the same or different, but it is preferable that they be the same.

[0131] (2) Next, a styrene polymer and an amine compound are added to solvent A to obtain a mixture A (S131). At this time, the timing of adding the styrene polymer and amine compound to solvent A is not particularly limited. (a) A solution may be prepared by dissolving a styrene polymer in solvent A, and then an amine compound may be dissolved or dispersed in the resulting solution to obtain a mixture A. (b) A mixture may be prepared by dissolving or dispersing an amine compound in solvent A, and then a styrene polymer may be dissolved in the resulting mixture to obtain mixture A. (c) The amine compound and the styrene polymer may be added to solvent A simultaneously, and then all components may be mixed to obtain mixture A. In this case, the amount of the amine compound should be, for example, 5% to 60% by mass relative to 100% by mass of solvent A. Furthermore, the amount of styrene polymer may be, for example, 0.3% to 30% by mass relative to 100% by mass of solvent A.

[0132] (3) Separately from step (2) above, a diisocyanate compound is added to solvent B to obtain a mixed solution B' (S132). In this case, the amount of the diisocyanate compound should be, for example, 5% to 60% by mass relative to 100% by mass of solvent B.

[0133] (4) Next, mixture A and mixture B' are mixed to react the amine compound with the diisocyanate compound to synthesize diurea (S133). This process can be carried out in the same manner as step (4) of manufacturing method A1, except that mixture B is replaced with mixture B'.

[0134] In steps (2) to (4) above, the mixing of the amine compound, diisocyanate compound, and styrene polymer into their respective solvents, as well as the mixing of mixture A and mixture B', can be carried out using, for example, a mechanical stirrer or a magnetic stirrer. Among these, the method using a mechanical stirrer is preferred because it facilitates the uniform mixing of each component.

[0135] By going through steps (1) to (4) as described above, a mixture containing diurea, a styrene-based polymer, solvent A, and solvent B can be obtained.

[0136] (5) Remove solvent A and solvent B from the mixture obtained in step (4) above (S134). This process can be carried out in the same manner as in step (5) of manufacturing method A1.

[0137] (6) Next, the mixture remaining after removing solvents A and B is washed (S135). This washing process removes any unreacted amine compounds or diisocyanate compounds that remain in the mixture. This process can be carried out in the same manner as step (6) of manufacturing method A1.

[0138] (7) The washed mixture is recovered to obtain mixture C containing diurea and a styrene polymer (S136). The resulting mixture C may be subjected to diurea pulverization as needed. Pulverization can be performed to finely and homogenize the thickener. When performing the above-mentioned grinding process, it is preferable to use a small grinder (for example, Lab Millser, manufactured by Osaka Chemical Co., Ltd.) because it can be carried out with simple equipment and at low cost.

[0139] (8) Next, the base oil is added to mixture C containing diurea and styrene polymer, and the two are mixed (S137). Specific examples of the above-mentioned base oils are as described above. The mixing of mixture C with the base oil may be carried out in the same manner as in step (8) of manufacturing method A1.

[0140] The above-mentioned grease composition can also be manufactured by going through such a process.

[0141] [A modified example of manufacturing method A] In manufacturing methods A1 to A3, after mixing mixture C with the base oil, a homogenization process using a roll mill or the like may be performed as needed. Furthermore, when producing a grease composition containing additives in addition to mixture C and base oil, for example, the base oil and mixture C may be mixed first, and then the necessary additives may be mixed, or the base oil, mixture C, and necessary additives may be mixed simultaneously.

[0142] (c) The steps of removing solvent A and solvent B (S114, S124, S134) and washing the mixture (S115, S125, S135) may be performed in reverse order. In this case, for example, the following methods may be employed. The above mixture, in which diurea is dispersed in solvents A and B, is placed in a separatory funnel, and water is then added to the separatory funnel to transfer the unreacted amine compound and unreacted diisocyanate compound to the aqueous phase. Next, the water containing the unreacted amine compound and diisocyanate compound is removed from the separatory funnel. Subsequently, solvents A and B are removed from the mixture washed using the separatory funnel by the method of removing solvents A and B (S114, S124, S134).

[0143] The steps of washing the mixture (S115, S125, S135) are not mandatory and may be omitted. After the steps for synthesizing diurea (S113, S123, S133), a base oil may be added to the mixture obtained in the diurea synthesis step before the steps for removing solvent A and solvent B (S114, S124, S134). In this case, the step of adding the base oil to mixture C (S117, S127, S137) is unnecessary.

[0144] Method A, which includes a step of synthesizing diurea in the presence of a styrene-based polymer, is suitable as a method for producing a grease composition that has good oil retention and can ensure low torque.

[0145] (Manufacturing method B) Examples of specific embodiments of manufacturing method B include manufacturing methods B1 to B3.

[0146] [Manufacturing method B1] Figure 10 is a process diagram illustrating method B1 for manufacturing the grease composition. (1) In manufacturing method B1, first, predetermined amounts of amine compound, diisocyanate compound, styrene polymer, and base oil are prepared. Specific examples of amine compounds, diisocyanate compounds, styrene polymers, and base oils are as described above.

[0147] (2) Half of the base oil is mixed with a portion of the styrene polymer and an amine compound to obtain a mixture D (S211). At this time, the timing of adding the styrene polymer and amine compound to the base oil is not particularly limited. (a) After mixing a styrene-based polymer with the base oil, an amine compound may be further mixed in. (b) After mixing the amine compound with the base oil, a styrene polymer may be further mixed in. (c) The amine compound and the styrene polymer may be added to the base oil simultaneously, and then all the components may be mixed.

[0148] (3) The remaining styrene polymer and diisocyanate compound are added to the remaining base oil to obtain a mixture E (S212). In this case, the timing of adding the styrene polymer and diisocyanate compound to the base oil is not particularly limited. (a) After mixing a styrene-based polymer with the base oil, a diisocyanate compound may be further mixed in. (b) After mixing a diisocyanate compound with the base oil, a styrene polymer may be further mixed in. (c) A diisocyanate compound and a styrene polymer may be added to the base oil simultaneously, and then all components may be mixed.

[0149] (4) Mixing solution D containing the amine compound with mixture E containing the diisocyanate compound, the amine compound and the diisocyanate compound are reacted to synthesize diurea (S213). Here, you can either stir mixture D while adding mixture E dropwise to mix the two, or stir mixture E while adding mixture D dropwise to mix the two.

[0150] The mixing of mixture D and mixture E may be carried out at room temperature or under heating. If the process is carried out under heating, the heating temperature should be, for example, between 150°C and 180°C. The mixture of mixture D and mixture E may be mixed in such a ratio of 2 to 2.2 moles of amine compound to 1 mole of diisocyanate compound. The reaction time between the amine compound and the diisocyanate compound is not particularly limited; any time sufficient for the reaction to proceed adequately is acceptable. Specifically, for example, a reaction time of 0.5 hours or more and 2 hours or less is appropriate.

[0151] In steps (2) to (4) above, the mixing of the amine compound, diisocyanate compound, and styrene polymer into their respective base oils, as well as the mixing of mixture D and mixture E, can be carried out using, for example, a mechanical stirrer or a magnetic stirrer. Among these, the method using a mechanical stirrer is preferred because it facilitates the uniform mixing of each component.

[0152] By going through steps (1) to (4) as described above, a grease composition containing diurea and a styrene-based polymer in a base oil can be produced.

[0153] [Manufacturing method B2] Figure 11 is a process diagram illustrating method B2 for manufacturing the grease composition. (1) In manufacturing method B2, first, predetermined amounts of amine compound, diisocyanate compound, styrene polymer, and base oil are prepared. Specific examples and preferred examples of amine compounds, diisocyanate compounds, styrene polymers, and base oils are as described above.

[0154] (2) Add the amine compound to half the amount of base oil to obtain a mixed solution D' (S221).

[0155] (3) Add the styrene polymer and the diisocyanate compound to the remaining base oil to obtain a mixture E (S222). In this case, the timing of adding the styrene polymer and diisocyanate compound to the base oil is not particularly limited. (a) After mixing a styrene-based polymer with the base oil, a diisocyanate compound may be further mixed in. (b) After mixing a diisocyanate compound with the base oil, a styrene polymer may be further mixed in. (c) A diisocyanate compound and a styrene polymer may be added to the base oil simultaneously, and then all components may be mixed.

[0156] (4) Mix the mixture D' containing the amine compound with the mixture E containing the diisocyanate compound to react the amine compound with the diisocyanate compound and synthesize diurea (S223). This process can be carried out in the same manner as step (4) of manufacturing method B1, except that mixture D is replaced with mixture D'.

[0157] In steps (2) to (4) above, the mixing of the amine compound, diisocyanate compound, and styrene polymer into their respective base oils, as well as the mixing of mixture D' and mixture E, can be carried out using, for example, a mechanical stirrer or a magnetic stirrer. Among these, the method using a mechanical stirrer is preferred because it facilitates the uniform mixing of each component.

[0158] A grease composition containing diurea and a styrene-based polymer in a base oil can also be produced by going through the steps (1) to (4) described above.

[0159] [Manufacturing method B3] Figure 12 is a process diagram illustrating method B3 for manufacturing the grease composition. (1) In manufacturing method B3, first, predetermined amounts of amine compound, diisocyanate compound, styrene polymer, and base oil are prepared. Specific examples and preferred examples of amine compounds, diisocyanate compounds, styrene polymers, and base oils are as described above.

[0160] (2) Add a styrene polymer and an amine compound to half the amount of base oil to obtain a mixture D (S231). At this time, the timing of adding the styrene polymer and amine compound to the base oil is not particularly limited. (a) After mixing a styrene-based polymer with the base oil, an amine compound may be further mixed in. (b) After mixing the amine compound with the base oil, a styrene polymer may be further mixed in. (c) The amine compound and the styrene polymer may be added to the base oil simultaneously, and then all the components may be mixed.

[0161] (3) Add the diisocyanate compound to the remaining base oil to obtain the mixture E' (S232).

[0162] (4) Mixture D containing the amine compound and mixture E' containing the diisocyanate compound are mixed to react the amine compound with the diisocyanate compound and synthesize diurea (S233). This process can be carried out in the same manner as step (4) of manufacturing method B1, except that mixture E is replaced with mixture E'.

[0163] In steps (2) to (4) above, the mixing of the amine compound, diisocyanate compound, and styrene polymer into their respective base oils, as well as the mixing of mixture D and mixture E', can be carried out using, for example, a mechanical stirrer or a magnetic stirrer. Among these, the method using a mechanical stirrer is preferred because it facilitates the uniform mixing of each component.

[0164] A grease composition containing diurea and a styrene-based polymer in a base oil can also be produced by going through the steps (1) to (4) described above.

[0165] [Variations of manufacturing method B] In manufacturing methods B1 to B3, after synthesizing diurea, homogenization treatment using a roll mill or the like may be performed as needed. Furthermore, when producing a grease composition containing additives in addition to a base oil, diurea, and a styrene-based polymer, for example, the diurea can be synthesized first, and then the necessary additives can be mixed in.

[0166] In manufacturing method B1, the amount of styrene polymer added to mixture D and the amount of styrene polymer added to mixture E may be the same or different. In manufacturing 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.

[0167] In steps (2) to (4) of manufacturing method B1, a mixture D' obtained by mixing a base oil with an amine compound and a mixture E' obtained by mixing a base oil with a diisocyanate compound may be prepared, and then the mixture D' and mixture E' may be mixed with a styrene-based polymer.

[0168] Method B, which includes a step of synthesizing diurea in the presence of a styrene-based polymer, is also suitable as a method for producing a grease composition that has good oil retention and is suitable for ensuring low torque. [Examples]

[0169] Next, the invention of this disclosure will be described in more detail based on examples, but the invention of this disclosure is not limited to the examples.

[0170] The following raw materials were used in the examples / comparative examples. • Diisocyanate compound: 4,4′-diphenylmethane diisocyanate (MDI) • Amine compound: Octylamine • Base oil: Poly-α-OLEPONE: PAO8 (base oil kinematic viscosity at 40°C is 46 mmHg) 2 / s) • Solvent: Toluene • Styrene polymer: Styrene-isoprene copolymer (manufactured by Lubrizol Nippon Co., Ltd., Lubrizol 7306) • Acrylic polymer: Alkyl methacrylate copolymer (manufactured by Sanyo Chemical Industries, Acruve V-1001)

[0171] (Example 1) (1) A styrene-isoprene copolymer was dissolved in toluene. Furthermore, a predetermined amount of octylamine was mixed into the resulting solution to obtain mixed solution A1. (2) Separately from the above step (1), a predetermined amount of MDI was mixed with a solution of styrene-isoprene copolymer dissolved in toluene to obtain mixed solution B1. Here, the amount of styrene-isoprene copolymer added to obtain mixture A1 and the amount of styrene-isoprene copolymer added to obtain mixture B1 were the same.

[0172] In steps (1) and (2), the amounts of octylamine and MDI were such that the mixing ratio of the two (octylamine:MDI) was 2:1 in molar ratio, and the amount of diurea produced was 40% by mass relative to 100% by mass of toluene. Furthermore, the amount of styrene-isoprene copolymer added was set so that the amount of styrene-isoprene copolymer contained in mixture C of diurea and styrene-isoprene copolymer, as described later, was 7.00% by mass relative to the total amount of diurea and styrene-isoprene copolymer. Mixture A1 was prepared by adding styrene-isoprene copolymer and octylamine while stirring toluene with a mechanical stirrer. Furthermore, the mixture B1 was prepared by adding styrene-isoprene copolymer and MDI while stirring toluene with a mechanical stirrer.

[0173] (3) Mixture A1 was stirred with a mechanical stirrer while mixture B1 was added dropwise to mixture A1 to mix the two. After the dropwise addition of mixture B1 was complete, octylamine and MDI were reacted at room temperature while stirring was continued for 0.5 hours to produce diurea.

[0174] (4) Subsequently, the mixture containing diurea, styrene-isoprene copolymer and toluene was left at room temperature for 24 hours to evaporate and remove the toluene, thereby producing mixture C (thickener) of diurea and styrene-isoprene copolymer.

[0175] (5) PAO8, which is the base oil at room temperature, was mixed with mixture C at room temperature and heated to 150°C while stirring with a mechanical stirrer. The base oil mixed with mixture C was maintained at 170°C and stirred with a mechanical stirrer for 30 minutes. After that, it was allowed to cool to room temperature while continuing to stir with a mechanical stirrer, and stirring was stopped. In this case, the amount of PAO8 (base oil) was set to be 70.00% by mass of the total amount of PAO8 and mixture C. Subsequently, a homogenization process using a roll mill was performed to complete the grease composition.

[0176] The diurea produced in this embodiment has the following structural formula. TIFF0007838580000001.tif13120

[0177] (Example 2) A grease composition was completed in the same manner as in Example 1, except that the amount of styrene-isoprene copolymer added was changed so that the amount of styrene-isoprene copolymer in mixture C was 14.00% by mass relative to the total amount of diurea and styrene-isoprene copolymer.

[0178] (Comparative Example 1) A grease composition was completed in the same manner as in Example 1, except that the amount of styrene-isoprene copolymer added was changed so that the amount of styrene-isoprene copolymer in mixture C was 1.00% by mass relative to the total amount of diurea and styrene-isoprene copolymer.

[0179] (Comparative Example 2) (1) A predetermined amount of octylamine was mixed with toluene to obtain mixture A2. (2) Separately from the process in (1) above, a predetermined amount of MDI was mixed with toluene to obtain mixture B2.

[0180] In the steps (1) and (2), the amounts of the octylamine and the MDI were such that the mixing ratio of the two (octylamine:MDI) was 2:1 in molar ratio, and the amount of the produced diurea was 40% by mass based on 100% by mass of toluene. The preparation of the mixed solution A2 was carried out by adding octylamine while stirring toluene with a mechanical stirrer. Also, the preparation of the mixed solution B1 was carried out by adding MDI while stirring toluene with a mechanical stirrer.

[0181] (3) While stirring the mixed solution A2 with a mechanical stirrer, the mixed solution B2 was dropped into the mixed solution A2 to mix the two. After the dropping of the mixed solution B2 was completed, while continuing stirring for 0.5 hours, octylamine and MDI were reacted at room temperature to produce diurea.

[0182] (4) Thereafter, the mixture containing diurea and toluene was left standing at room temperature for 24 hours to evaporate and remove toluene, and diurea (thickener) was produced.

[0183] (5) The room-temperature diurea obtained in (4) was put into PAO8 as the base oil at room temperature, and heated to 150°C while stirring with a mechanical stirrer. While maintaining the base oil mixed with diureia at 170°C, stirring was continuously carried out with a mechanical stirrer for 30 minutes. Thereafter, while continuously stirring with a mechanical stirrer, it was allowed to cool to room temperature and the stirring was stopped. At this time, the amount of PAO8 (base oil) was set to be 70.00% by mass based on the total amount of PAO8 and the mixture C. Thereafter, a homogenization treatment using a roll mill was carried out to complete the grease composition.

[0184] The structural formula of the diurea produced in this Comparative Example 2 is the same as that in Example 1. The grease composition produced in this Comparative Example 2 does not contain a styrene-isoprene copolymer.

[0185] (Comparative Example 3) A grease composition was completed in the same manner as in Example 1, except that an acrylic polymer (alkyl methacrylate copolymer) was used instead of the styrene-isoprene copolymer.

[0186] (Comparative Example 4) (1) Diurea was produced in the same manner as in steps (1) to (4) of Comparative Example 2. (2) Styrene-isoprene copolymer and the room-temperature diurea obtained in (1) were added to PAO8 (room temperature) as the base oil, and the mixture was heated to 150°C while stirring with a mechanical stirrer. The base oil mixture of styrene-isoprene copolymer and diurea was maintained at 170°C and stirred with a mechanical stirrer for 30 minutes. After that, the mixture was allowed to cool to room temperature while continuing to stir with a mechanical stirrer, and stirring was stopped.

[0187] In this case, the amount of PAO8 (base oil) was set to 70.00% by mass relative to the total amount of PAO8, styrene-isoprene copolymer, and diurea. Furthermore, the amount of styrene-isoprene copolymer was set to 7.00% by mass relative to the total amount of styrene-isoprene copolymer and diurea. Subsequently, a homogenization process using a roll mill was performed to complete the grease composition.

[0188] (Example 3) (1) Use PAO8 as the base oil and heat this base oil to 100°C. (2) Base oil, styrene-isoprene copolymer, octylamine, and 4,4'-diphenylmethane diisocyanate (MDI) were weighed. The amounts of octylamine and MDI were weighed so that the mixing ratio (octylamine:MDI) of the two was 2:1 in molar ratio. Here, the amount of base oil was set to be 85.00% by mass of the total amount of PAO8 and thickener (styrene-isoprene copolymer and diurea produced through subsequent processes). Furthermore, the amount of styrene-isoprene copolymer was set to 7.00% by mass of the total amount of styrene-isoprene copolymer and the resulting diurea.

[0189] (3) Half of the base oil (100°C), half of the styrene-isoprene copolymer, and octylamine were placed in stainless steel container A and stirred at 100°C for 30 minutes to obtain mixed solution D1. (4) In another stainless steel container B, the remaining half of the base oil (100°C), the remaining half of the styrene-isoprene copolymer, and the MDI were added and stirred at 100°C for 30 minutes to obtain the mixture E1.

[0190] (5) Mixture D1 containing octylamine in stainless steel container A was dropped into stainless steel container B and gradually added to mixture E1 containing MDI. (6) After confirming that the entire contents of the mixed liquid D1 in stainless steel container A had been poured into stainless steel container B, the temperature was raised to 170°C. (7) While heating, the mixture was stirred and the temperature was maintained at 170°C for 30 minutes. (8) The heating was stopped, and the mixture was allowed to cool naturally while stirring until it reached 100°C. (9) After confirming that the temperature had fallen below 100°C, stirring was stopped and the mixture was allowed to cool naturally to room temperature. (10) The grease composition was completed by homogenization treatment using a roll mill.

[0191] (Comparative Example 5) (1) Use PAO8 as the base oil and heat this base oil to 100°C. (2) Base oil, octylamine, and 4,4'-diphenylmethane diisocyanate (MDI) were weighed. The amounts of octylamine and MDI were weighed so that the mixing ratio (octylamine:MDI) of the two was 2:1 in molar ratio. Here, the amount of base oil was set to be 85.00% by mass of the total amount of PAO8 and thickener (diurea produced through a subsequent process).

[0192] (3) Half of the base oil (100°C) and octylamine were added to stainless steel container A, and the mixture was stirred at 100°C for 30 minutes to obtain mixed solution D2. (4) Pour the remaining half amount of base oil (100 °C) and MDI into another stainless steel container B, and stir at 100 °C for 30 minutes to obtain a mixed solution E2.

[0193] (5) The mixed solution D2 containing octylamine in the stainless steel container A was dropped into the stainless steel container B and gradually added to the mixed solution E2 containing MDI. (6) After confirming that the total amount of the mixed solution D2 in the stainless steel container A was completely added to the stainless steel container B, the temperature was raised to 170 °C. (7) Stir while heating and keep the temperature at 170 °C for 30 minutes. (8) Stop heating and let it cool naturally while stirring until it cools to 100 °C. (9) After confirming that the temperature has dropped below 100 °C, stop stirring and let it cool naturally until it reaches room temperature. (10) Perform a homogenization treatment with a roll mill to complete the grease composition. The grease composition produced in Comparative Example 5 does not contain a styrene-isoprene copolymer. [[ID=…]](比較例6) (1) In the same manner as in steps (1) to (9) of Comparative Example 5, a composition containing base oil and diurea was obtained. (2) Add the styrene-isoprene copolymer dissolved in a solvent (toluene) to the composition obtained in (1) and stir at room temperature for 30 minutes. At this time, the amount of the styrene-isoprene copolymer was set to an amount such that it would be 7.00% by mass based on the total amount of the styrene-isoprene copolymer and diurea. (3) Stir while heating and keep the temperature at 100 °C for 30 minutes to evaporate and remove toluene. Thereafter, perform a homogenization treatment using a roll mill to complete the grease composition.

[0195] The following evaluations were performed on the grease compositions produced in the examples and comparative examples. The results are shown in Table 3. 1. Penetration (60W) ​​The consistency (60W) of the grease compositions prepared in the examples and comparative examples was measured according to the method conforming to JIS K 2220.

[0196] 2.Oil separation degree The degree of oil separation was measured for the grease compositions prepared in the examples and comparative examples (excluding the grease compositions of Comparative Examples 4 and 6) using a method compliant with JIS K 2220 11. The results are shown in Table 1. In this experiment, the sample amount was 10g, the test temperature was 150°C, and the test duration was 24 hours. Two samples were used, and the average value was used as the evaluation result.

[0197] 3. Bearing rotation torque The bearing rotation torque of the grease compositions prepared in the examples and comparative examples (excluding the grease compositions of Comparative Examples 3, 4, and 6) was measured using a rotation torque tester according to the conditions in Table 1 below. Here, the grease compositions prepared in the examples and comparative examples were respectively sealed into a test bearing, 6202 2RUCM (with non-contact seals on both sides), in such a manner that the grease composition constituted 35% by volume relative to the volume of the space enclosed by the inner ring, outer ring, and seals, excluding the balls and cage. This test bearing is installed in the testing machine and tested for 1800 min. -1 The bearing was rotated for 30 minutes, and the average torque during the last minute was defined as the bearing rotation torque. The sample size was 2, and the average value was used as the evaluation result. In this evaluation, it is considered that a rotational torque of 12 mN·m or less indicates good low torque performance, and a rotational torque of 10 mN·m or less indicates even better low torque performance.

[0198] [Table 1]

[0199] 4. Measurement of the average particle size of the thickener The average particle size of the thickener contained in the grease compositions prepared in the examples and comparative examples was measured using a confocal laser microscope (Leica Microsystems, TCS SP08). The configuration of the confocal laser microscope shown in Table 2 was used. This device has built-in software (Leica Application Suite X (LAS X) Version 4.4.0) that can calculate the average particle diameter of the observed material. Using this software, the volume of the thickener can be calculated for each particle from the acquired 3D image, the diameter of each particle can be calculated assuming the shape of each particle is a perfect sphere, and the average value of the diameters of each particle can be calculated as the measured value (average particle diameter). The average diameter of the obtained thickeners is shown in Table 3.

[0200] [Table 2]

[0201] [Table 3]

[0202] As shown in Table 3, the thickener contained in the grease composition according to the embodiment of this disclosure has an average diameter of particles with a diameter of 0.2 μm or more of 0.2 μm or more and 1.0 μm or less. Furthermore, it was found that the above grease composition has a low oil separation rate (0.2% or less) and good oil retention properties. In addition, it was found that the above grease composition has good low torque properties. [Explanation of symbols]

[0203] 1: Dual-pinion type electric power steering system, 2: Steering shaft, 3: Steering gear system, 33: Housing 31: Rack shaft, 310: First rack tooth section, 311: First rack tooth, 312: Cylindrical surface, 313: Cylindrical surface, 314: Second rack tooth section, 315: Second rack tooth, 32: First pinion shaft, 320: First pinion teeth, 321: First pinion teeth, 392: First seat member 54: Second pinion shaft, 540: Second pinion teeth, 541: Second pinion teeth, 592: Second seat member 601: Column-type electric power steering system, 602: Steering shaft, 603: Steering gear system, 633: Housing 631: Rack shaft, 710: Rack teeth, 711: Rack teeth, 712: Cylindrical surface 632: Pinion shaft, 720: Pinion teeth, 721: Pinion teeth, 792: Seat member 801: Ball bearing, 802: Inner ring, 803: Outer ring, 804: Balls, 805: Cage, 806: Seal G Grease Composition

Claims

1. Styrene-based polymers and Amine compounds and, Isocyanate compounds and, Lubricant and A first solvent that does not dissolve the generated urea compound, Prepare a second solvent that does not dissolve the generated urea compound, The amine compound is dissolved or dispersed in the first solvent, the isocyanate compound is dissolved or dispersed in the second solvent, and the styrene polymer is dissolved or dispersed in one or both of the first and second solvents to prepare a first mixture containing at least the amine compound and a second mixture containing at least the isocyanate compound. The first mixture and the second mixture are mixed, and the amine compound and the isocyanate compound are reacted to produce a third mixture containing the styrene polymer and the urea compound. A method for producing a grease composition, comprising removing the first solvent and the second solvent from the third mixture, adding the lubricating oil, and ensuring that the content of the styrene polymer is 2% by mass or more and 30% by mass or less relative to the total amount of the styrene polymer and the urea compound.

2. The method for producing the grease composition according to Claim 1, wherein the content of the styrene polymer is 2% by mass or more and 20% by mass or less with respect to the total amount of the styrene polymer and the urea compound.

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