Grease composition and method for producing grease composition

Abstract

A grease composition, wherein the grease composition contains a base oil and a thickener, the thickener contains a urea compound and a styrene-based polymer, the content of the styrene-based polymer is 2 mass% or more and 30 mass% or less relative to the total amount of the urea compound and the styrene-based polymer, and the average value of diameters of particles having a diameter of 0.2 μm or more in the thickener is 0.2 μm or more and 1.0 μm or less.

Description

Technical Field

[0001] This disclosure relates to grease compositions and methods for manufacturing grease compositions.

[0002] This application claims priority based on International Patent Application PCT / JP 2021 / 027389, filed on July 21, 2021, the entire contents of which are set forth in the aforementioned International Patent Application. Background Technology

[0003] Grease compositions are used for lubrication of sliding parts such as rolling bearings and gears.

[0004] Lubricating grease compositions are described in Patent Documents 1 to 7.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2015-193858

[0008] Patent Document 2: Japanese Patent Application Publication No. 2013-227438

[0009] Patent Document 3: Japanese Patent Application Publication No. 2012-177105

[0010] Patent Document 4: Japanese Patent Application Publication No. 2007-297422

[0011] Patent Document 5: US Patent No. 5,207,935

[0012] Patent Document 6: Japanese Patent Application Publication No. 2002-327188

[0013] Patent Document 7: International Publication No. 2019 / 017227 Summary of the Invention

[0014] The problem that the invention aims to solve

[0015] For grease compositions used for lubricating rolling bearings, gears, etc., good oil retention is required to ensure good lubrication. Furthermore, to meet the needs of energy saving and high efficiency in rolling bearings, gears, etc., the aforementioned grease compositions are required to reduce torque.

[0016] That is, a grease composition is required that has good oil retention properties and can ensure low torque when used in rolling bearings, gears, etc.

[0017] Methods for solving problems

[0018] One aspect of this disclosure relates to a grease composition comprising a base oil and a thickener.

[0019] The aforementioned thickeners include urea compounds and styrene polymers.

[0020] Relative to the combined amount of the urea compound and the styrene polymer, the content of the styrene polymer is 2% by mass or more and 30% by mass or less.

[0021] The average diameter of the particles with a diameter of 0.2 μm or more in the above thickeners is 0.2 μm or more and 1.0 μm or less.

[0022] In another embodiment of the method for manufacturing a grease composition disclosed herein, the following steps are taken:

[0023] Styrene polymers,

[0024] amine compounds,

[0025] Isocyanate compounds,

[0026] lubricating oil,

[0027] The first solvent that does not dissolve the generated urea compound, and

[0028] The second solvent does not dissolve the generated urea compound.

[0029] 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, thereby preparing a first mixture containing at least the amine compound and a second mixture containing at least the isocyanate compound.

[0030] The first mixture and the second mixture are mixed to react the amine compound and the isocyanate compound, thereby generating a third mixture containing the styrene polymer and the urea compound.

[0031] Remove the first solvent and the second solvent from the third mixture, and then add the lubricating oil.

[0032] In another embodiment of the method for manufacturing a grease composition disclosed herein, the following steps are taken:

[0033] Styrene polymers,

[0034] amine compounds,

[0035] Isocyanate compounds,

[0036] First lubricating oil, and

[0037] Second lubricating oil,

[0038] 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 polymer is dissolved or dispersed in one or both of the first and second lubricating oils, thereby preparing a fourth mixture containing at least the amine compound and a fifth mixture containing at least the isocyanate compound.

[0039] The fourth and fifth mixtures are mixed to react the amine compound with the isocyanate compound.

[0040] Invention Effects

[0041] The grease composition disclosed herein has excellent oil retention properties.

[0042] The grease composition disclosed herein ensures low torque when used in rolling bearings, gears, etc.

[0043] The method for manufacturing the grease composition according to this disclosure can be used to properly manufacture the grease composition of this disclosure. Attached Figure Description

[0044] [ Figure 1 This diagram schematically illustrates an example of a dual-pinion type electric power steering system containing a grease composition.

[0045] [ Figure 2 ]for Figure 1 AA section diagram.

[0046] [ Figure 3 ]for Figure 1 BB cross-sectional view.

[0047] [ Figure 4 This diagram schematically illustrates an example of a column-type electric power steering system containing a grease composition.

[0048] [ Figure 5 ]for Figure 4 AA section diagram.

[0049] [ Figure 6 [This is a cross-sectional view of a rolling bearing encapsulated with a grease composition.]

[0050] [ Figure 7 This is a process diagram illustrating method A1 for manufacturing a lubricating grease composition.

[0051] [ Figure 8 This is a process diagram illustrating method A2 for manufacturing a lubricating grease composition.

[0052] [ Figure 9 This is a process diagram illustrating method A3 for manufacturing a lubricating grease composition.

[0053] [ Figure 10 This is a process diagram illustrating method B1 for manufacturing a lubricating grease composition.

[0054] [ Figure 11 This is a process diagram illustrating method B2 for manufacturing a lubricating grease composition.

[0055] [ Figure 12 This is a process diagram illustrating method B3 for manufacturing a lubricating grease composition. Detailed Implementation

[0056] <Summary of Embodiments of the Invention as disclosed herein>

[0057] The following is a summary description of embodiments of the invention disclosed herein.

[0058] (1) One embodiment of the grease composition of this disclosure comprises a base oil and a thickener.

[0059] The aforementioned thickeners include urea compounds and styrene polymers.

[0060] Relative to the combined amount of the urea compound and the styrene polymer, the content of the styrene polymer is 2% by mass or more and 30% by mass or less.

[0061] The average diameter of the particles with a diameter of 0.2 μm or more in the above thickeners is 0.2 μm or more and 1.0 μm or less.

[0062] The above-described grease composition contains a urea compound and a predetermined amount of a styrene polymer as a thickener, and the average diameter of the particles with a diameter of 0.2 μm or more in the thickener is 0.2 μm or more and 1.0 μm or less. That is, the above-described grease composition does not contain coarse thickener particles that would easily occur if the urea compound were contained alone. Therefore, the above-described grease composition retains oil well. In other words, the above-described grease composition has good oil retention properties. Furthermore, the above-described grease composition enables rolling bearings, gears, etc., to operate at low torque. In other words, the above-described grease composition has good low-torque properties.

[0063] On the other hand, none of the aforementioned patent documents 1 to 7 describe a method that combines good oil retention and good low torque performance by using a urea compound and a predetermined amount of styrene polymer as a thickener and by setting the average diameter of particles with a diameter of 0.2 μm or more in the thickener to be 0.2 μm or more and 1.0 μm or less.

[0064] (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, relative to the total amount of the urea compound and the styrene polymer.

[0065] (3) In the grease composition of (1) or (2) above, the urea compound is preferably a diurea.

[0066] Under these conditions, the grease composition is not easily degraded even when used at high temperatures. In other words, the above-mentioned grease composition has good heat resistance.

[0067] (4) In any one of the above (1) to (3) grease compositions, the base oil is preferably a poly-α-olefin.

[0068] In this case, the grease composition exhibits excellent flowability at low temperatures. In other words, the grease composition described above has good low-temperature flowability. Furthermore, it does not easily degrade components, such as rubber or resin components, located around the lubricated sliding surfaces of rolling bearings, gears, etc. In other words, the grease composition described above has weak aggression towards rubber or resin components.

[0069] (5) In any one of the above (1) to (4) grease compositions, the content of the thickener is preferably 10% by mass or more and 40% by mass or less relative to the total amount of the base oil and the thickener.

[0070] In this case, the grease composition exhibits better low-torque properties.

[0071] (6) In a method for manufacturing a grease composition according to one embodiment of the present disclosure, the following steps are taken:

[0072] Styrene polymers,

[0073] amine compounds,

[0074] Isocyanate compounds,

[0075] lubricating oil,

[0076] The first solvent that does not dissolve the generated urea compound, and

[0077] The second solvent does not dissolve the generated urea compound.

[0078] The first mixture is prepared by dissolving or dispersing the amine compound and the styrene polymer in the first solvent.

[0079] The second mixture is prepared by dissolving or dispersing the isocyanate compound and the styrene polymer in the second solvent.

[0080] The first mixture and the second mixture are mixed to react the amine compound and the isocyanate compound, generating a third mixture containing the styrene polymer and the urea compound.

[0081] Remove the first solvent and the second solvent from the third mixture, and then add the lubricating oil.

[0082] (7) In another embodiment of the method for manufacturing a grease composition according to the present disclosure, the following preparation is made:

[0083] Styrene polymers,

[0084] amine compounds,

[0085] Isocyanate compounds,

[0086] lubricating oil,

[0087] The first solvent that does not dissolve the generated urea compound, and

[0088] The second solvent does not dissolve the generated urea compound.

[0089] The first mixture is prepared by dissolving or dispersing the amine compound in the first solvent.

[0090] The isocyanate compound and the styrene polymer are dissolved or dispersed in the second solvent to prepare a second mixture.

[0091] The first mixture and the second mixture are mixed to react the amine compound and the isocyanate compound, generating a third mixture containing the styrene polymer and the urea compound.

[0092] Remove the first solvent and the second solvent from the third mixture, and then add the lubricating oil.

[0093] (8) In another embodiment of the method for manufacturing a grease composition according to the present disclosure, the following are prepared:

[0094] Styrene polymers,

[0095] amine compounds,

[0096] Isocyanate compounds,

[0097] lubricating oil,

[0098] The first solvent that does not dissolve the generated urea compound, and

[0099] The second solvent does not dissolve the generated urea compound.

[0100] The first mixture is prepared by dissolving or dispersing the amine compound and the styrene polymer in the first solvent.

[0101] The isocyanate compound is dissolved or dispersed in the second solvent to prepare a second mixture.

[0102] The first mixture and the second mixture are mixed to react the amine compound and the isocyanate compound, generating a third mixture containing the styrene polymer and the urea compound.

[0103] Remove the first solvent and the second solvent from the third mixture, and then add the lubricating oil.

[0104] (9) In another embodiment of the method for manufacturing a grease composition according to the present disclosure, the following preparation is made:

[0105] Styrene polymers,

[0106] amine compounds,

[0107] Isocyanate compounds,

[0108] First lubricating oil, and

[0109] Second lubricating oil,

[0110] The above-mentioned amine compound and the above-mentioned styrene polymer are dissolved or dispersed in the above-mentioned first lubricating oil to prepare a fourth mixture.

[0111] The isocyanate compound and the styrene polymer are dissolved or dispersed in the second lubricating oil to prepare the fifth mixture.

[0112] The fourth and fifth mixtures are mixed to react the amine compound with the isocyanate compound.

[0113] (10) In another embodiment of the method for manufacturing a grease composition according to the present disclosure, the following are prepared:

[0114] Styrene polymers,

[0115] amine compounds,

[0116] Isocyanate compounds,

[0117] First lubricating oil, and

[0118] Second lubricating oil,

[0119] The fourth mixture is prepared by dissolving or dispersing the aforementioned amine compound in the first lubricating oil.

[0120] The isocyanate compound and the styrene polymer are dissolved or dispersed in the second lubricating oil to prepare the fifth mixture.

[0121] The fourth and fifth mixtures are mixed to react the amine compound with the isocyanate compound.

[0122] (11) In another embodiment of the method for manufacturing a grease composition according to the present disclosure, the following are prepared:

[0123] Styrene polymers,

[0124] amine compounds,

[0125] Isocyanate compounds,

[0126] First lubricating oil, and

[0127] Second lubricating oil,

[0128] The above-mentioned amine compound and the above-mentioned styrene polymer are dissolved or dispersed in the above-mentioned first lubricating oil to prepare a fourth mixture.

[0129] The isocyanate compound is dissolved or dispersed in the second lubricating oil to prepare the fifth mixture.

[0130] The fourth and fifth mixtures are mixed to react the amine compound with the isocyanate compound.

[0131] According to the manufacturing methods described in (6) to (11), the grease composition involved in the embodiments of this disclosure can be appropriately manufactured.

[0132] <Detailed description of embodiments of the invention disclosed herein>

[0133] The following describes embodiments of the invention disclosed herein.

[0134] It should be noted that the embodiments described in this disclosure are illustrative in all respects and not restrictive. The scope of the invention is defined by the claims and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0135] First, an apparatus using the grease composition of this disclosure will be described, and then embodiments related to the grease composition of this disclosure will be described.

[0136] The grease compositions disclosed herein are used, for example, in dual pinion type electric power steering systems, column type electric power steering systems, rolling bearings, etc.

[0137] Dual-pinion type electric power steering system

[0138] Figure 1 A schematic diagram illustrating an example configuration of a dual pinion type electric power steering system 1 including a steering gear assembly 3.

[0139] Figure 2 To illustrate a portion of the steering gear assembly 3 Figure 1 AA section view. In Figure 2 In the middle, the lower part of the diagram corresponds to the lower side in the vertical direction when mounted on a vehicle.

[0140] Figure 3 To illustrate a portion of the steering gear assembly 3 Figure 1 BB cross-sectional view. In Figure 3 In the middle, the lower part of the diagram corresponds to the lower side in the vertical direction when mounted on a vehicle.

[0141] The dual-pinion type electric power steering system 1 includes: 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 includes: a controller 50, a torque sensor 51, a 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 includes a worm 531 and a worm wheel 532.

[0142] A driver operating a car equipped with the dual-pinion type electric power steering system 1 performs steering operations by rotating the steering wheel 10. The steering shaft 2 includes a column shaft 21, a first universal joint 23, an intermediate shaft 22, and a second universal joint 24. The first universal joint 23 includes: 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 includes: 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).

[0143] A steering wheel 10 is fixed to one end of a column shaft 21 in the extending direction. A first yoke of a first universal joint 23 is fixed to the other end of the column shaft 21 in the extending direction. The column shaft 21 is rotatable about a central axis in the extending direction. The first yoke is pivotally engaged with a first pair of trunnions on the same central axis of the first cross shaft via a plurality of first rolling elements. A second yoke is pivotally engaged with 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 intersect at a 90-degree angle with the central axes of the second pair of trunnions.

[0144] The second yoke of the first universal joint 23 fixes one end of the intermediate shaft 22 in its extension direction. The third yoke of the second universal joint 24 is fixed at the other end of the intermediate shaft 22 in its extension direction. The third yoke is pivotally engaged with the 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 pivotally engaged with the 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 its extension direction. Thus, when the driver rotates the steering wheel 10, the column shaft 21 rotates around its central axis in its extension direction, the intermediate shaft 22 also rotates around its central axis in its extension direction, and the first pinion shaft 32 also rotates around its central axis in its extension direction.

[0145] In the dual-pinion type electric power steering device 1, the first pinion shaft 32, rack shaft 31, housing 33, two rack bushings 30 and 34, first bearing 35, second bearing 36, first rack guide plate mechanism 39, electric motor 52, reduction mechanism 53, second pinion shaft 54, third bearing 55, fourth bearing 56, worm housing 57, and second rack guide plate mechanism 59 constitute the steering gear device 3 as a rack and pinion type steering device. Figure 1 In the diagram, the shell 33 is represented by an imaginary line (double-dotted line), and its interior is shown.

[0146] The first pinion shaft 32 extends from the upper side to the lower side in the vertical direction of the vehicle. Along its extension direction, 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. Serrations are formed on the serrated portion 324. The serrations of the serrated portion 324 are fixed to the fourth yoke of the second universal joint 24. The first shaft portion 322 is cylindrical. The first pinion tooth portion 320 has first pinion teeth 321 formed on its entire circumferential surface. The extension direction of the first pinion teeth 321 has an angle other than 90 degrees relative to the extension direction of the central axis of the first pinion shaft 32. The first boss portion 323 is cylindrical.

[0147] The housing 33 has a first opening 332 on the steering wheel 10 side, and the side opposite to the first opening 332 is sealed. A first pinion shaft 32 is housed inside the housing 33. The first pinion shaft 32 is rotatably supported relative to the housing 33 by two bearings 35 and 36. The first bearing 35 is a ball bearing. The first bearing 35 includes an inner ring, an outer ring, and balls. The inner ring is fixed to the first shaft portion 322, and the outer ring is fixed to the housing 33. The balls roll on the inner and outer rings. The second bearing 36 is a roller bearing. The second bearing 36 includes rollers and an outer ring. The outer ring is fixed to the housing 33, and the rollers roll on the outer peripheral surface of the first boss portion 323 and the outer ring.

[0148] With the first pinion shaft 32, the first bearing 35, and the second bearing 36 inserted into the housing 33, a cover 37, through which the first pinion shaft 32 passes, is fixed to the first opening 332 of the housing. A seal is fixed to the cover 37 and is slidable on the outer peripheral surface 322b of the first shaft portion 322 of the first pinion shaft 32. A cover member 38 is also 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 radially outer side.

[0149] The rack shaft 31 has the following components extending from one end to the other: 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. The first rack tooth portion 310 has a first rack tooth 311 formed on a portion of its circumferential direction, and the remaining portion is a cylindrical surface 312 centered on the extending direction of the rack shaft 31. The second rack tooth portion 314 has a second rack tooth 315 formed on a portion of its circumferential direction, and the remaining portion is a cylindrical surface 313 centered on the extending direction of the rack shaft 31. 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 centered on the extending direction of the rack shaft 31. The extending direction of the first rack tooth 311 has an angle other than 90 degrees relative to the extending direction of the rack shaft. The extension direction of the second rack tooth 315 has an angle other than 90 degrees with respect to the extension direction of the rack shaft 31. When the angle of the first rack tooth 311 with respect to the extension direction of the rack shaft 31 is X, the angle of the second rack tooth 315 with respect to the extension direction of the rack shaft 31 is π-X.

[0150] The housing 33 extends in a direction different from the first opening 332 on the steering wheel 10 side, having a second opening 333 at one end of the extending direction and a third opening 334 at the other end. A rack shaft 31 is housed inside the housing 33 along its extending direction. A first cylindrical portion 316 at one end of the rack shaft 31 protrudes from the second opening 333 at one end of the extending direction of the housing 33. A third cylindrical portion 318 at the other end of the extending direction of the rack shaft 31 protrudes from the third opening 334 at the other end of the extending direction of the housing 33. The housing 33 has a fourth opening 335. The fourth opening 335 is located closer to the other end of the housing's extending direction than the first opening 332. The housing 33 also 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, radially about the extending direction of the housing 33 as its central axis, and in a direction perpendicular to the first opening 332. The sixth opening 337 and the fourth opening 335 are located at approximately the same position in the extending direction of the housing 33, in the radial direction with the extending direction of the housing 33 as the central axis, and in a direction perpendicular to the fourth opening 335.

[0151] The first rack bushing 30 is fixed to one end of the housing 33 in the extending direction. The first rack bushing 30 is abutted against the second opening 333 and fixed to the housing 33. The first rack bushing 30 is slidable on the outer circumferential surface of the first cylindrical portion 316 of the rack shaft 31. The second rack bushing 34 is fixed to the other end of the housing 33 in the extending direction. The second rack bushing 34 is abutted against the third opening 334 and fixed to the housing 33. The second rack bushing 34 is slidable on the outer circumferential surface of the third cylindrical portion 318 of the rack shaft 31.

[0152] The first pinion tooth 321 formed on the first pinion tooth portion 320 of the first pinion shaft 32 and the first rack tooth 311 formed on the first rack tooth portion 310 of the rack shaft 31 are in contact in a rolling sliding manner via a grease composition G. The first pinion tooth 321 and the first rack tooth 311 mesh via the grease composition G. When the first pinion shaft 32 rotates relative to the housing 33 with its central axis in its extending direction as the center, the rack shaft 31 moves in a linear direction relative to the housing 33 in the extending direction of the housing 33.

[0153] The first rack guide plate mechanism 39 is fixed to the housing 33. The first rack guide plate mechanism 39 is fixed to the fifth opening 336. The fifth opening 336 is located on the cylindrical surface 312 side of the rack shaft 31, which is the other part of the rack shaft 310 in the circumferential direction of the first rack tooth portion 310, at the position where the first pinion shaft 32 meshes with the rack shaft 31 in the extending direction of the housing 33.

[0154] The first rack guide plate mechanism 39 includes: a first support yoke 391, a first plate member 392, a first helical spring 393, and a first plug 394. The first plate member 392 is sandwiched between the cylindrical surface 312 of the rack shaft 31, which is the other circumferential part of the first rack tooth 310, and the cylindrical surface of the first support yoke 391. The first plate member 392 is fixed to the first support yoke 391. The first plate member 392 and the cylindrical surface 312 of the rack shaft 31, which is the other circumferential part of the first rack tooth 310, are in slidable 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 contacts one end of the first helical spring 393. The first support yoke 391 contacts the other end of the first helical spring 393. The first helical spring 393 becomes shorter than its free length when the first plug 394 is fixed to the fifth opening 336. Therefore, the first component 392 is pressed against the rack shaft 31 relative to the housing 33.

[0155] The second pinion shaft 54 ​​extends from the upper side to the lower side in the vertical direction of the vehicle. Along its extension direction, the second pinion shaft 54 ​​has a mating portion 544, a second shaft portion 542, a second pinion tooth portion 540, and a second boss portion 543. The mating portion 544 is cylindrical. The second shaft portion 542 is cylindrical. The second pinion tooth portion 540 has second pinion teeth 541 formed on its entire circumferential surface. The extension direction of the second pinion teeth 541 has an angle other than 90 degrees with respect to the extension direction of the central axis of the second pinion shaft 54. The second boss portion 543 is cylindrical.

[0156] The worm gear 532 engages with the fitting part 544. The worm 531 is fixed to the output shaft 521 of the motor 52. The motor 52 is fixed to the worm housing 57. The worm housing 57 has a seventh opening 571. The output shaft 521 of the motor 52 is disposed in the internal space of the worm housing 57 via the seventh opening 571. The motor 52 is fixed to the worm housing 57 by blocking the seventh opening 571 of the worm housing 57.

[0157] The worm 531 is disposed within the internal space of the worm housing 57. The worm wheel 532 is disposed within the internal space of the worm housing 57. The worm housing 57 has an eighth opening 572 above the plumb bob, through which the assembly of the second pinion shaft 54 ​​and the worm wheel 532 is inserted into the internal space of the worm housing 57. The eighth opening is closed by a cover 58. The worm housing 57 has a ninth opening 573 on the side opposite to the eighth opening 572. A portion of the second shaft portion 542 of the second pinion shaft 54, the second pinion tooth portion 540, and the second boss portion 543 protrude from the ninth opening 573 of the worm housing 57.

[0158] The worm housing 57 is fixed to the housing 33. The ninth opening 573 of the worm housing 57 communicates with the fourth opening 335 of the housing 33, sealing the internal space from the external space.

[0159] The third bearing 55 is a ball bearing. Bearing 55 includes an inner ring, an outer ring, and balls. The inner ring is fixed to the second shaft portion 542, and the outer ring is fixed to the worm housing 57. The balls roll on the inner and outer rings. Bearing 56 is a roller bearing. Bearing 56 includes rollers and an outer ring. The outer ring is fixed to the housing 33, and the rollers roll on the outer circumferential surface of the second boss portion 543 and the outer ring.

[0160] The second pinion tooth 541 formed on the second pinion tooth portion 540 of the second pinion shaft 54 ​​and the second rack tooth 315 formed on the second rack tooth portion 314 of the rack shaft 31 are in contact in a rolling sliding manner via the grease composition G. The second pinion tooth 541 and the second rack tooth 315 mesh via the grease composition G. When the second pinion shaft 54 ​​rotates relative to the housing 33 with its central axis in its extending direction as the center, the rack shaft 31 moves in a linear direction relative to the housing 33 in the extending direction of the housing 33.

[0161] The housing 33 is fixed with a second rack guide mechanism 59. The second rack guide mechanism 59 is fixed on a sixth opening 337. The sixth opening 337 is located on the cylindrical surface 313 side of the rack shaft 31, which is the other part of the rack shaft 31 that serves as the circumferential part of the second rack tooth 314, at the position where the second pinion shaft 54 ​​meshes with the rack shaft 31 in the extending direction of the housing 33.

[0162] The second rack guide plate mechanism 59 includes: a second support yoke 591, a second plate member 592, a second helical spring 593, and a second plug 594. The second plate member 592 is sandwiched between the cylindrical surface 313 of the rack shaft 31, which is the other circumferential part of the second rack tooth 314, and the cylindrical surface of the second support yoke 591. The second plate member 592 is fixed to the second support yoke 591. The second plate member 592 and the cylindrical surface 313 of the rack shaft 31, which is the other circumferential part of the second rack tooth 314, are in slidable 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 contacts one end of the second helical spring 593. The second support yoke 591 contacts the other end of the second helical spring 593. The second helical spring 593 becomes shorter than its free length when the second plug 594 is fixed to the sixth opening 337. Therefore, the second component 592 is pressed against the rack shaft 31 relative to the housing 33.

[0163] 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 consisting of a worm gear 531 that rotates integrally with the output shaft 521 of the motor 52 and a worm wheel 532 that rotates integrally with the second pinion shaft 54. The controller 50 supplies motor current to the motor 52. Based on the steering torque, vehicle speed, etc., detected by the torque sensor 51, the controller 50 controls the motor 52, transmitting the rotational force of the output shaft 521 of the motor 52, 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.

[0164] In a vehicle (not shown), housing 33 is fixed such that its extension direction aligns with the vehicle's width direction. Ball joint sockets 11, 11 are fixed to one and the other ends of rack shaft 31, respectively. Steering tie rods 12, 12, connected to these ball joint sockets 11, 11, are connected via steering knuckle arms 13, 13 to the raceways of rolling bearings that rotatably support a pair of left and right front wheels 14, 14. Rack shaft 31 moves linearly along the extension direction of housing 33, thereby steering the left and right front wheels 14, 14, which act as steering wheels.

[0165] A grease composition G is sealed inside the housing 33. The grease composition G lubricates the two sliding surfaces by being sandwiched between the rolling sliding surfaces of the first pinion teeth 321 and the first rack teeth 311, which are in contact due to meshing. The grease composition G also lubricates the two sliding surfaces by being sandwiched between the sliding surface of the first piece member 392 and the rack shaft 31, which are in contact due to pressing against each other, and the cylindrical surface 312 of the rack shaft 31, which is the other circumferential part of the first rack tooth portion 310. Finally, the grease composition G lubricates the two sliding surfaces by being sandwiched between the rolling sliding surfaces of the second pinion teeth 541 and the second rack teeth 315, which are in contact due to meshing. The grease composition G lubricates the sliding surfaces of the two sliding surfaces by being sandwiched between the sliding surface of the second member 592 and the sliding surface of the cylindrical surface 313 of the rack shaft 31, which is the other circumferential part of the second rack tooth 314, which are pressed against each other by the second member 592 and the rack shaft 31.

[0166] The steering gear assembly 3 configured in this way is insulated with the grease composition of this disclosure as grease composition G. Because the grease composition of this disclosure ensures oil retention, the steering gear assembly 3 exhibits good resistance to burning and sticking, and good wear resistance.

[0167] Column-type electric power steering system

[0168] Figure 4 This diagram schematically illustrates an example of the configuration of a column-type electric power steering system 601, which includes a steering gear assembly 603.

[0169] Figure 5 To illustrate a portion of the steering gear assembly 603 Figure 4 AA section view. In Figure 5 In the middle, the lower part of the diagram corresponds to the lower side in the vertical direction when mounted on a vehicle.

[0170] The column-type electric power steering system 601 includes: 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 performs steering operations by rotating the steering wheel 610. The steering shaft 602 includes: a column shaft 621, a first universal joint 623, an intermediate shaft 622, and a second universal joint 624. The first universal joint 623 includes: 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 includes: 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).

[0171] A steering wheel 610 is fixed to one end of a column shaft 621 in the extending direction. A 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 a central axis in the extending direction. The first yoke is pivotally engaged with a first pair of trunnions on the same central axis of the first cross shaft via a plurality of first rolling elements. A second yoke is pivotally engaged with 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 intersect at a 90-degree angle with the central axes of the second pair of trunnions.

[0172] The second yoke of the first universal joint 623 fixes one end of the intermediate shaft 622 in its extension direction. The third yoke of the second universal joint 624 is fixed at the other end of the intermediate shaft 622 in its extension direction. The third yoke is pivotally engaged with the 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 pivotally engaged with the 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 intersect the central axes of the fourth pair of trunnions at a 90-degree angle. The fourth yoke of the second universal joint 624 fixes one end of the pinion shaft 632 in its extension direction. Thus, when the driver rotates the steering wheel 610, the column shaft 621 rotates around its central axis in its extension direction, the intermediate shaft 622 also rotates around its central axis in its extension direction, and the pinion shaft 632 also rotates around its central axis in its extension direction.

[0173] In the column-type electric power steering system 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 steering system. Figure 4 In the diagram, the shell 633 is represented by an imaginary line (double-dotted line), and its interior is shown.

[0174] The pinion shaft 632 extends from the upper side to the lower side in the vertical direction of the vehicle. Along its extension direction, the pinion shaft 632 has a serrated portion 724, a shaft portion 722, a pinion tooth portion 720, and a boss portion 723 from one end to the other. Serrations are formed on the serrated portion 724. The serrations of the serrated portion 724 are fixed to the fourth yoke of the second universal joint 624. The shaft portion 722 is cylindrical. The pinion tooth portion 720 has pinion teeth 721 formed on its entire circumferential surface. The extending direction of the pinion teeth 721 has an angle other than 90 degrees relative to the extending direction of the central axis of the pinion shaft 632. The boss portion 723 is cylindrical.

[0175] The housing 633 has a first opening 732 on the steering wheel 610 side, and the side opposite to the first opening 732 is sealed. A pinion shaft 632 is housed inside the housing 633. The pinion shaft 632 is rotatably supported relative to the housing 633 by two bearings 635 and 636. Bearing 635 is a ball bearing. Bearing 635 includes an inner ring, an outer ring, and balls; the inner ring is fixed to the shaft portion 722, and the outer ring is fixed to the housing 633; ​​the balls roll on the inner and outer rings. Bearing 636 is a roller bearing. Bearing 636 includes rollers and an outer ring; the outer ring is fixed to the housing 633, and the rollers roll on the outer peripheral surface of the boss portion 723 and the outer ring.

[0176] With the pinion shaft 632 and the two bearings 635 and 636 inserted into the housing 633, a cover 637, through which the pinion shaft 632 passes, is fixed to the first opening 732 of the housing. 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 also fixed to the housing 633. The cover member 638 covers a portion of the shaft portion 722 of the pinion shaft 632 from the radially outer side.

[0177] The rack shaft 631 has, from one end to the other in the extending direction, a first cylindrical portion 716, a rack tooth portion 710, and a second cylindrical portion 717. The rack tooth portion 710 has rack teeth 711 formed on a portion of its circumferential direction, and the remaining portion in the circumferential direction is a cylindrical surface 712 with the extending direction 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 respectively cylindrical surfaces with the extending direction of the rack shaft 631 as their central axis. The extending direction of the rack teeth 711 has an angle other than 90 degrees relative to the extending direction of the rack shaft 631.

[0178] The housing 633 extends in a direction different from the first opening 732 on the steering wheel 610 side, having a second opening 733 at one end in the extending direction and a third opening 734 at the other end. A rack shaft 631 is received inside the housing 633 along its extending direction. One end of the rack shaft 631 protrudes from the second opening 733 at that end of the housing 633. The other end of the rack shaft 631 protrudes from the third opening 734 at the other end of the housing 633.

[0179] The first rack bushing 630 is fixed to one end of the housing 633 in the extending direction. The first rack bushing 630 is abutted against the second opening 733 and fixed to the housing 633. The first rack bushing 630 is slidable on the outer circumferential surface of the first cylindrical portion 716 of the rack shaft 631. The second rack bushing 634 is fixed to the other end of the housing 633 in the extending direction. The second rack bushing 634 is abutted against the third opening 734 and fixed to the housing 633. The second rack bushing 634 is slidable on the outer circumferential surface of the second cylindrical portion 717 of the rack shaft 631.

[0180] The pinion teeth 721 formed on the pinion tooth portion 720 of the pinion shaft 632 and the rack teeth 711 formed on the rack tooth portion 710 of the rack shaft 631 are in contact in a rolling sliding manner via the grease composition G. The pinion teeth 721 and the rack teeth 711 mesh via the grease composition G. When the pinion shaft 632 rotates relative to the housing 633 with its central axis in its extending direction as the center, the rack shaft 631 moves in a straight line relative to the housing 633 in the extending direction of the housing 633.

[0181] In a vehicle (not shown), housing 633 is fixed such that its extending direction aligns with the vehicle's width direction. Ball joint sockets 11, 11 are fixed to one and the other ends of rack shaft 31, respectively. Steering tie rods 12, 12, connected to these ball joint sockets 11, 11, are connected via steering knuckle arms 13, 13 to the raceways of rolling bearings that rotatably support a pair of left and right front wheels 14, 14. Rack shaft 31 moves linearly along the extending direction of housing 33, thereby steering the left and right front wheels 14, 14, which act as steering wheels.

[0182] A rack guide plate mechanism 639 is fixed on the housing 633. The housing 633 has a fourth opening 736 on the cylindrical surface 712 side of the rack shaft 631, which is the other part of the rack tooth 710 in the circumferential direction, at the position where the pinion shaft 632 meshes with the rack shaft 631 in the extending direction.

[0183] The rack guide mechanism 639 includes a support yoke 791, a plate member 792, a helical spring 793, and a plug 794. The plate member 792 is sandwiched between a cylindrical surface 712 of the rack shaft 631 (which is the other circumferential part of the rack teeth 710) and a cylindrical surface of the support yoke 791. The plate member 792 is fixed to the support yoke 791. The plate member 792 and the cylindrical surface 712 of the rack shaft 631 (which is the other circumferential part of the rack teeth 710) are in slidable contact via a grease composition G. The plug 794 is fixed to a fourth opening 736 of the housing 633. The plug 794 contacts one end of the helical spring 793. The support yoke 791 contacts the other end of the helical spring 793. The helical spring 793 becomes shorter than its free length when the plug 794 is fixed to the fourth opening 736. Therefore, the plate member 792 is pressed against the rack shaft 631 relative to the housing 633.

[0184] 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 formed by meshing a worm gear 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. The controller 40 supplies electric current to the electric motor 42. The controller 40 controls the electric motor 42 based on the steering torque, vehicle speed, etc. detected by the torque sensor 41, and the rotational force of the output shaft 421 of the electric motor 42, reduced by the reduction mechanism 43, is applied to the column shaft 621 as a steering assist force.

[0185] A grease composition G is sealed inside the housing 633. The grease composition G lubricates the two rolling sliding surfaces by being sandwiched between the rolling sliding surfaces of the pinion teeth 721 and the rack teeth 711, which are in contact due to meshing. The grease composition G also lubricates the two sliding surfaces by being sandwiched between the sliding surface of the plate member 792 and the rack shaft 631, which are in contact due to pressing against each other. The grease composition G lubricates the two sliding surfaces by being sandwiched between the sliding surface of the plate member 792 and the cylindrical surface 712 of the rack shaft 631, which is the other circumferential part of the rack tooth portion 710.

[0186] The steering gear assembly 603 configured in this way is insulated with the grease composition of this disclosure as grease composition G. Because the grease composition of this disclosure ensures oil retention, the steering gear assembly 603 exhibits good resistance to burning and sticking, and good wear resistance.

[0187] Rolling bearings

[0188] Figure 6 This is a cross-sectional view of ball bearing 801, which is an example of a rolling bearing.

[0189] The ball bearing 801 includes: an inner ring 802, an outer ring 803 disposed radially outside the inner ring 802, a plurality of rolling balls 804 disposed between the inner ring 802 and the outer ring 803, and an annular retainer 805 holding the rolling balls 804. Additionally, seals 806 are provided on one axial side and the other axial side of the ball bearing 801.

[0190] Furthermore, a grease composition G is sealed in the annular region 807 between the inner ring 802 and the outer ring 803.

[0191] The inner ring 802 has an inner raceway surface 821 formed on its outer periphery for the balls 804 to roll.

[0192] The outer ring 803 has an outer raceway surface 831 formed on its inner circumference for the balls 804 to roll.

[0193] Multiple balls 804 are sandwiched between the inner raceway surface 821 and the outer raceway surface 831, and roll on the inner raceway surface 821 and the outer raceway surface 831.

[0194] The grease composition G sealed in region 807 is also sandwiched in the contact area between the ball 804 and the inner raceway surface 821 of the inner ring 802, and the contact area between the ball 804 and the outer raceway surface 831 of the outer ring 803. It should be noted that the grease composition G is sealed in such a way that, relative to the volume of the space after removing the ball 804 and the retainer 805 from the space enclosed by the inner ring 802, the outer ring 803 and the seal 806, the grease composition G accounts for more than 20% and less than 40% by volume.

[0195] The seal 806 is an annular member having an annular mandrel 806a and an elastic member 806b fixed to the mandrel 806a. The radially outer portion is fixed to the outer ring 803, and the radially inner portion is mounted on the inner ring 802 in a sliding contact manner. The seal 806 prevents the sealed grease composition G from leaking to the outside.

[0196] The ball bearing 801 configured in this way is encapsulated with the grease composition of this disclosure as grease composition G. Because the grease composition of this disclosure ensures oil retention, the ball bearing 801 exhibits good resistance to burning and sticking, and good wear resistance.

[0197] The grease composition disclosed herein can be used in the aforementioned dual pinion type electric power steering system, column type electric power steering system, rolling bearing, etc.

[0198] Lubricating Grease Compositions

[0199] The grease compositions described in this disclosure include a base oil and a thickener, wherein the thickener comprises a urea compound and a styrene polymer.

[0200] (Base oil)

[0201] Examples of base oils mentioned above include: poly-α-olefin (PAO), ester oils, polyalkylene glycols, fluorinated oils, silicone oils, and ether oils.

[0202] Poly-α-olefin (PAO) is preferred. This is because the grease composition exhibits good low-temperature fluidity by using poly-α-olefin. Furthermore, the grease composition exhibits low aggression towards rubber and resin components.

[0203] Examples of the aforementioned poly-α-olefins include substances obtained by oligomerizing or polymerizing α-olefins such as 1-hexene, 1-octene, 1-nonene, 1-decene, 1-dodecene, and 1-tetradecene, as well as substances obtained by hydrogenating them.

[0204] As the above-mentioned poly-α-olefin, PAO4 to PAO8 obtained by oligomerizing 1-decene are preferred.

[0205] The preferred dynamic viscosity of the base oil at 40°C is 20 mm. 2 / second or higher and 60mm 2 / s or less. In this case, the above-mentioned grease composition is suitable for achieving low torque.

[0206] The preferred dynamic viscosity (40°C) of the aforementioned base oil is 25 mm. 2 / second or higher and 50mm 2 / second or less.

[0207] The dynamic viscosity of the base oils mentioned above is based on JIS K 2283.

[0208] (Thickener)

[0209] The thickener described above is a mixture containing urea compounds and styrene polymers.

[0210] When the grease composition contains a thickener comprising urea compounds and styrene polymers, the grease composition exhibits good oil retention and is suitable for ensuring low torque performance.

[0211] [Urea compounds]

[0212] Examples of the aforementioned urea compounds include, for example, urea compounds such as diurea, triurea, tetraurea, polyurea (other than diurea, triurea, and tetraurea), urea-carbamate compounds, carbamate compounds such as dicarbamates, or mixtures thereof.

[0213] From the viewpoint that the above-mentioned urea compound has good heat resistance, a diurea represented by the following structural formula (1) is preferred.

[0214] R 1 -NHCONH-R 2 -NHCONH-R 3 …(1)

[0215] (In equation (1), R) 1 and R 3 Each represents an amino residue independently, R 2 This indicates a diisocyanate residue.

[0216] The diurea represented by the above structural formula (1) is a reaction product of an amine compound and a diisocyanate compound.

[0217] The aforementioned amine compounds can be any amine compounds known for their use in the synthesis of diureas, which are known as thickeners.

[0218] Examples of the aforementioned amine compounds include alkylamines, alkylanilines, and cyclohexylamines.

[0219] From the viewpoints of the grease composition having good low torque properties and good heat resistance, alkylamines are preferred.

[0220] The diisocyanate compound mentioned above can be any diisocyanate compound known as a diisocyanate compound used in the synthesis of diurea, which is known as a thickener.

[0221] Examples of the diisocyanate compounds mentioned above include 2,4-toluene diisocyanate (2,4-TDI), 2,6-toluene diisocyanate (2,6-TDI), mixtures of 2,4-TDI and 2,6-TDI, and 4,4'-diphenylmethane diisocyanate (MDI).

[0222] Relative to the total amount of the base oil and the thickener, the content of the thickener is preferably 10% by mass or more and 40% by mass or less.

[0223] The reason is that the grease composition has good low torque properties.

[0224] 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.

[0225] The above reaction can be carried out, for example, in (a) a base oil or in (b) a solvent. When carried out in a base oil, the resulting mixture can be used as a grease composition. When carried out in a solvent, by removing the solvent, powdered diurea is obtained, and then the powdered diurea is mixed with the base oil to obtain a grease composition.

[0226] The method for manufacturing the above-mentioned grease composition is described in detail below.

[0227] [Styrene polymers]

[0228] The aforementioned styrene polymers are polymers that contain styrene or its derivatives as monomer components.

[0229] The aforementioned styrene-based polymers can be homopolymers of styrene or its derivatives, or copolymers of a first monomer component selected from styrene and its derivatives with other monomer components. These other monomer components can also be styrene or its derivatives, as long as they differ from the first monomer component.

[0230] Examples of the aforementioned copolymers include random copolymers, alternating copolymers, block copolymers, and graft copolymers.

[0231] Examples of homopolymers of the aforementioned styrene include: atactic polystyrene, isotactic polystyrene, poly(p-methylstyrene), poly(p-ethylstyrene), poly(p-isopropylstyrene), poly(α-methylstyrene), etc.

[0232] Examples of copolymers include copolymers of a first monomer component selected from styrene and its derivatives with styrene or its derivatives other than the first monomer component.

[0233] Examples of copolymers described above include copolymers of the first monomer component and a diene. Examples of the diene include butadiene, isoprene, pentadiene, and hexadiene.

[0234] As the copolymer mentioned above, styrene-isoprene copolymer is preferred.

[0235] In the above styrene-isoprene copolymer, the ratio (molar ratio) of styrene to isoprene can be set as styrene:isoprene = 1:9 to 9:1.

[0236] The copolymers mentioned above are not limited to copolymers with two monomer components, but can also be copolymers with three or more monomer components.

[0237] The number-average molecular weight of the above-mentioned styrene polymers is preferably 10,000 or more and 500,000 or less, more preferably 20,000 or more and 200,000 or less.

[0238] The number-average molecular weights were determined using gel permeation chromatography.

[0239] Commercially available products can also be used as the aforementioned styrene polymers.

[0240] Specific examples of commercially available products include: Lubrizol (registered trademark) 7306 (manufactured by Lubrizol Corporation of Japan), Lubrizol 7308, Lubrizol 7460, Infineum (registered trademark) SV140 (manufactured by Infineum Corporation), Infineum 150, Infineum 160, Septon (registered trademark) 1001 (manufactured by Kuraray Corporation), Septon 1020, etc.

[0241] 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 urea compound and the styrene polymer.

[0242] When the content of the aforementioned styrene polymers is less than 2% by mass, the grease composition does not exhibit good oil retention and good low-torque properties. On the other hand, even when the content exceeds 30% by mass, the oil retention of the grease composition hardly improves.

[0243] From the viewpoint of ensuring good oil retention and good low torque, the content of the styrene polymer is preferably 2% by mass or more and 20% by mass or less, 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 polymer.

[0244] In the above-described grease composition, the average diameter of the thickener particles with a diameter of 0.2 μm or more is 0.2 μm or more and 1.0 μm or less. The average diameter of the thickener is the average diameter calculated from the volume of the particle, assuming the shape of the thickener particles to be perfectly spherical.

[0245] The diameter of the aforementioned thickener particles was measured using a confocal laser microscope with a laser of wavelength 488 nm as the excitation light.

[0246] In observations of thickeners using a confocal laser microscope, particles with a diameter less than 0.2 μm cannot be observed due to the microscope's limited resolution. Therefore, the grease composition of this disclosure specifies the average diameter of thickener particles with a diameter of 0.2 μm or more as the average diameter of the thickener.

[0247] This does not mean that the above-mentioned grease composition does not contain thickener particles with a diameter of less than 0.2 μm.

[0248] When the above-mentioned grease composition is irradiated with a laser with a wavelength of 488 nm, the urea compound constituting the thickener emits fluorescence, and thus the urea compound is observed in the form of a fluorescence image. Furthermore, in the above-mentioned grease composition, the styrene polymer exists in a state where it is entangled with the urea compound.

[0249] Therefore, in the grease compositions of this disclosure, the fluorescence image of the urea compound observed using a confocal laser microscope is regarded as the fluorescence image of the thickener particles.

[0250] In addition, in the above observation, the volume of the thickener particles was measured, the shape of the thickener particles was regarded as a perfect sphere, the diameter of the thickener particles was calculated from the measured volume, and their average value was calculated.

[0251] The average diameter mentioned above can be calculated using commercially available analysis software.

[0252] By setting the average diameter of particles with a diameter of 0.2 μm or more in the above thickener to be 0.2 μm or more and 1.0 μm or less, it is possible to balance the assurance of oil retention and the improvement of low torque performance.

[0253] When the average diameter exceeds 1.0 μm, the oil retention and low torque performance decrease.

[0254] On the other hand, as mentioned above, since thickener particles with a diameter less than 0.2 μm cannot be observed, the lower limit of the average diameter is 0.2 μm.

[0255] The above-described grease composition may contain additives without impairing the effects of this disclosure. Examples of such additives include: antioxidants, rust inhibitors, extreme pressure agents, wear-resistant agents, dyes, color stabilizers, thickeners, structure stabilizers, metal deactivators, viscosity index improvers, etc.

[0256] When the above-mentioned grease composition contains additives, the total content of the above-mentioned additives in the grease composition is preferably set to 10% by mass or less relative to the total mass of the base oil and the thickener.

[0257] As described above, the grease composition of this disclosure can be suitably used as a grease composition for sealing in gears such as electric power steering gears in automobiles, rolling bearings, etc.

[0258] Method for manufacturing lubricating grease compositions

[0259] As a method for manufacturing the grease composition disclosed herein, it may be adopted by (a) synthesizing a urea compound in a solvent and then mixing the obtained urea compound with a base oil (hereinafter also referred to as manufacturing method A) or (b) synthesizing a urea compound in a base oil (hereinafter also referred to as manufacturing method B).

[0260] The aforementioned 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. Hereinafter, the method for manufacturing the above-mentioned grease composition will be described using a diisocyanate compound as the isocyanate compound and synthesizing a diurea as the urea compound as an example.

[0261] (Manufacturing Method A)

[0262] As a specific implementation of manufacturing method A, manufacturing methods A1 to A3 can be exemplified, for example.

[0263] [Manufacturing Method A1]

[0264] Figure 7 This is a process diagram illustrating method A1 for manufacturing a lubricating grease composition.

[0265] (1) In manufacturing method A1, firstly, predetermined amounts of amine compound, diisocyanate compound, styrene polymer, solvent A and solvent B are prepared respectively.

[0266] Specific examples of amine compounds, diisocyanate compounds, and styrene polymers are as described above.

[0267] Solvent A and solvent B can each be solvents with boiling points lower than the prepared styrene polymer and capable of dissolving the prepared styrene polymer.

[0268] Specific examples of solvent A and solvent B mentioned above include: toluene, hexane, ethyl acetate, tetrahydrofuran, p-xylene, m-xylene, o-xylene, methyl acetate, etc. It should be noted that substances containing amine groups, hydroxyl groups, or other substances that react with substances containing isocyanate groups, or substances that react with substances containing amine groups, are preferably avoided when using solvent A and solvent B.

[0269] Solvent A and solvent B are preferably solvents with a viscosity lower than that of the prepared styrene polymer.

[0270] In this disclosure, the viscosity of the solvent and the styrene polymer is determined using a Cannon-Fensk viscometer according to the method of JIS Z8803:2011.

[0271] Solvent A and solvent B can be the same or different, but they are preferably the same.

[0272] In subsequent processes, when mixture A containing solvent A is mixed with mixture B containing solvent B, the two are reliably mixed, making it suitable for the reaction of amine compounds with diisocyanate compounds. Furthermore, in subsequent processes, when removing solvent A and solvent B, the removal method and conditions are easily selected.

[0273] (2) Next, a portion of the styrene polymer and an amine compound are added to solvent A to obtain mixture A (S111).

[0274] At this point, there are no particular restrictions on the timing of adding styrene polymers and amine compounds to solvent A.

[0275] (a) A solution can be prepared by dissolving a styrene polymer in solvent A, and then an amine compound can be dissolved or dispersed in the resulting solution to prepare a mixture A.

[0276] (b) Alternatively, an amine compound can be dissolved or dispersed in solvent A to prepare a mixture, and then a styrene polymer can be dissolved in the resulting mixture to prepare mixture A.

[0277] (c) Alternatively, an amine compound and a styrene polymer can be added to solvent A simultaneously, and then all components can be mixed to form a mixture A.

[0278] At this point, for example, relative to 100% by mass of solvent A, the amount of amine compound can be set to be more than 5% by mass and less than 60% by mass.

[0279] Additionally, for example, the amount of styrene polymer relative to 100% by mass of solvent A can be set to be 0.3% by mass or more and 30% by mass or less.

[0280] (3) Independent of the process in (2) above, the remaining styrene polymer and diisocyanate compound are added to solvent B to obtain mixture B (S112).

[0281] At this point, there are no particular restrictions on the timing of adding styrene polymers and diisocyanate compounds to solvent B.

[0282] (a) A solution can be prepared by dissolving a styrene polymer in solvent B, and then a diisocyanate compound can be dissolved or dispersed in the resulting solution to prepare a mixture B.

[0283] (b) Alternatively, a mixture can be prepared by dissolving or dispersing the diisocyanate compound in solvent B, and then dissolving the styrene polymer in the resulting mixture to produce mixture B.

[0284] (c) Alternatively, a diisocyanate compound and a styrene polymer may be added to solvent B simultaneously, and then all components may be mixed to form mixture B.

[0285] At this point, for example, relative to 100% by mass of solvent B, the amount of diisocyanate compound can be set to more than 5% by mass and less than 60% by mass.

[0286] Additionally, for example, the amount of styrene polymer relative to 100% by mass of solvent B can be set to 0.3% by mass or more and 30% by mass or less.

[0287] (4) Next, mix A and B to react the amine compound with the diisocyanate compound to synthesize diurea (S113).

[0288] Here, mixture B can be added dropwise to mixture A while stirring mixture A to mix the two, or mixture A can be added dropwise to mixture B while stirring mixture B to mix the two.

[0289] The mixing of mixture A and mixture B can be carried out at room temperature or under heating.

[0290] When heating is performed, the heating temperature can be set to, for example, above 40°C and below 110°C.

[0291] Mixture A and mixture B can be mixed in such a way that 2 to 2.2 moles of amine compound become 1 mole of diisocyanate compound.

[0292] There are no particular restrictions on the reaction time between the amine compound and the diisocyanate compound, as long as the reaction proceeds sufficiently. Specifically, for example, it can be set to be more than 0.2 hours and less than 5 hours.

[0293] In the steps (2) to (4) above, the mixing of the amine compound, diisocyanate compound, and styrene polymer into the solvent, as well as the mixing of mixture A and mixture B, can be performed using, for example, a mechanical stirrer or a magnetic stirrer. From the viewpoint of easily and uniformly mixing the components, the method using a mechanical stirrer is preferred.

[0294] By going through the steps (1) to (4), a mixture containing diurea, styrene polymer, solvent A and solvent B can be obtained.

[0295] (5) Remove solvent A and solvent B from the mixture obtained in step (4) above (S114).

[0296] There are no particular restrictions on the methods for removing solvent A and solvent B. Solvent A and solvent B can be vaporized at room temperature or, as needed, by appropriate heating, depressurization, stirring, etc. Specific methods can be selected according to the types of solvent A and solvent B, as exemplified below.

[0297] For example, one method can be listed that involves placing the mixture at room temperature and atmospheric pressure to vaporize solvent A and solvent B.

[0298] Alternatively, a method can be cited as an example of heating the mixture at atmospheric pressure and a temperature lower than the boiling points of solvent A and solvent B to vaporize solvent A and solvent B. In this case, heating conditions can be, for example, heating at atmospheric pressure in a constant temperature bath at 40°C for 5 hours or more but less than 10 hours.

[0299] These methods can be combined.

[0300] (6) Next, the mixture remaining after removing solvent A and solvent B is washed (S115).

[0301] This cleaning process can remove unreacted amine compounds and diisocyanate compounds remaining in the mixture.

[0302] Here, as specific examples of cleaning methods, the following methods can be listed, etc.

[0303] First, the mixture after removing solvents A and B is mixed with water and filtered using a membrane filter to recover the residue. Then, the residue is heated at a temperature lower than the boiling point of water and lower than the boiling point of styrene-based polymers to vaporize the water adhering to the residue and remove the water from the residue. Examples of heating conditions include heating at atmospheric pressure in a high-temperature bath at 80°C for 5 to 10 hours.

[0304] (7) The washed mixture is recovered to obtain a mixture C(S116) containing bisurea and styrene polymers.

[0305] If necessary, the resulting mixture C can be subjected to a pulverization process using bisurea. This pulverization process allows for the refinement and homogenization of the thickener.

[0306] In performing the above-mentioned pulverization process, from the viewpoint of being able to carry it out with a simple device and at low cost, it is preferable to use a small pulverizer (such as the one manufactured by Osaka Chemical Co., Ltd., or Labo Millser).

[0307] (8) Next, add base oil to the mixture C containing diurea and styrene polymers and mix the two (S117).

[0308] Specific examples of the base oils mentioned above are as described above.

[0309] Here, the mixture C can be added dropwise to the base oil while stirring it to mix the two, or the base oil can be added dropwise to the mixture C while stirring it to mix the two.

[0310] The mixing of the above-mentioned mixture C with the above-mentioned base oil is preferably carried out under heating. At this time, the heating temperature can be set, for example, to be above 130°C and below 180°C.

[0311] There are no particular restrictions on the mixing time of the above mixture C and the above base oil. For example, it can be set to more than 0.5 hours and less than 2 hours.

[0312] There are no particular limitations on the method of mixing the above mixture C and the base oil, as long as the two are mixed evenly. For example, methods such as using a mechanical stirrer or a magnetic stirrer can be used. Among these, from the viewpoint of easily mixing the two evenly, the method of using a mechanical stirrer is preferred.

[0313] By going through such a process, the above-mentioned grease composition can be manufactured.

[0314] [Manufacturing Method A2]

[0315] Figure 8 This is a process diagram illustrating method A2 for manufacturing a lubricating grease composition.

[0316] (1) In manufacturing method A2, firstly, predetermined amounts of amine compound, diisocyanate compound, styrene polymer, solvent A and solvent B are prepared respectively.

[0317] Specific examples and preferred examples of amine compounds, diisocyanate compounds and styrene polymers are as described above.

[0318] The specific examples, preferred examples, and preferred avoidance examples of the above solvents A and B are the same as those of manufacturing method A1.

[0319] Solvent A and solvent B can be the same or different, but they are preferably the same.

[0320] (2) Next, an amine compound is added to solvent A to obtain mixture A' (S121).

[0321] At this point, relative to 100% by mass of solvent A, the amount of amine compound can be set to, for example, 5% by mass or more and 60% by mass or less.

[0322] (3) Independent of the process in (2) above, a styrene polymer and a diisocyanate compound are added to solvent B to obtain mixture B (S122).

[0323] At this point, there are no particular restrictions on the timing of adding styrene polymers and diisocyanate compounds to solvent B.

[0324] (a) A solution can be prepared by dissolving a styrene polymer in solvent B, and then a diisocyanate compound can be dissolved or dispersed in the resulting solution to prepare a mixture B.

[0325] (b) Alternatively, a mixture can be prepared by dissolving or dispersing the diisocyanate compound in solvent B, and then dissolving the styrene polymer in the resulting mixture to produce mixture B.

[0326] (c) Alternatively, a diisocyanate compound and a styrene polymer may be added to solvent B simultaneously, and then all components may be mixed to form mixture B.

[0327] At this point, the amount of diisocyanate compound relative to 100% by mass of solvent B can be set, for example, to be 5% by mass or more and 60% by mass or less.

[0328] In addition, relative to solvent B 100% by mass, the amount of styrene polymer can be set to, for example, 0.3% by mass or more and 30% by mass or less.

[0329] (4) Next, mix A' and B to react the amine compound with the diisocyanate compound to synthesize diurea (S123).

[0330] This process can be carried out in the same way as process (4) of manufacturing method A1, except that mixture A is replaced with mixture A'.

[0331] In the steps (2) to (4) above, the mixing of the amine compound, the diisocyanate compound, and the styrene polymer into the solvent, as well as the mixing of mixture A' and mixture B, can be performed using, for example, a mechanical stirrer or a magnetic stirrer. From the viewpoint of easily and uniformly mixing the components, the method using a mechanical stirrer is preferred.

[0332] By going through the steps (1) to (4), a mixture containing diurea, styrene polymer, solvent A and solvent B can be obtained.

[0333] (5) Remove solvent A and solvent B from the mixture obtained in step (4) above (S124).

[0334] This process can be performed in the same way as process (5) of manufacturing method A1.

[0335] (6) Next, the mixture remaining after removing solvent A and solvent B is washed (S125).

[0336] This cleaning process can remove unreacted amine compounds and diisocyanate compounds remaining in the mixture.

[0337] This process can be performed in the same way as process (6) of manufacturing method A1.

[0338] (7) The washed mixture is recovered to obtain a mixture C(S126) containing bisurea and styrene polymers.

[0339] If necessary, the resulting mixture C can be subjected to a pulverization process using bisurea. This pulverization process allows for the refinement and homogenization of the thickener.

[0340] In performing the above-mentioned pulverization process, from the viewpoint of being able to carry it out with a simple device and at low cost, it is preferable to use a small pulverizer (e.g., manufactured by Osaka Chemical Co., Ltd., Labo Millser, etc.) for the pulverization process.

[0341] (8) Next, base oil is added to the mixture C containing diurea and styrene polymers, and the two are mixed (S127).

[0342] Specific examples of the base oils mentioned above are as described above.

[0343] The mixing of mixture C with the base oil can be carried out in the same manner as step (8) of manufacturing method A1.

[0344] By going through such a process, the aforementioned grease composition can also be manufactured.

[0345] [Manufacturing Method A3]

[0346] Figure 9 This is a process diagram illustrating method A3 for manufacturing a lubricating grease composition.

[0347] (1) In manufacturing method A3, firstly, predetermined amounts of amine compound, diisocyanate compound, styrene polymer, solvent A and solvent B are prepared respectively.

[0348] Specific examples and preferred examples of amine compounds, diisocyanate compounds and styrene polymers are as described above.

[0349] The specific examples, preferred examples, and preferred avoidance examples of the above solvents A and B are the same as those of manufacturing method A1.

[0350] Solvent A and solvent B can be the same or different, but they are preferably the same.

[0351] (2) Next, styrene polymers and amine compounds are added to solvent A to obtain mixture A (S131).

[0352] At this point, there are no particular restrictions on the timing of adding styrene polymers and amine compounds to solvent A.

[0353] (a) A solution can be prepared by dissolving a styrene polymer in solvent A, and then an amine compound can be dissolved or dispersed in the resulting solution to prepare a mixture A.

[0354] (b) Alternatively, an amine compound can be dissolved or dispersed in solvent A to prepare a mixture, and then a styrene polymer can be dissolved in the resulting mixture to prepare mixture A.

[0355] (c) Alternatively, an amine compound and a styrene polymer can be added to solvent A simultaneously, and then all components can be mixed to form a mixture A.

[0356] At this point, relative to 100% by mass of solvent A, the amount of amine compound can be set to, for example, 5% by mass or more and 60% by mass or less.

[0357] In addition, relative to 100% by mass of solvent A, the amount of styrene polymer can be set to, for example, 0.3% by mass or more and 30% by mass or less.

[0358] (3) Independent of the process in (2) above, a diisocyanate compound is added to solvent B to obtain mixture B' (S132).

[0359] At this point, the amount of diisocyanate compound relative to 100% by mass of solvent B can be set, for example, to be 5% by mass or more and 60% by mass or less.

[0360] (4) Next, mix A and B' to react the amine compound with the diisocyanate compound to synthesize diurea (S133).

[0361] This process can be carried out in the same way as process (4) of manufacturing method A1, except that mixture B is replaced with mixture B'.

[0362] In the steps (2) to (4) above, the mixing of the amine compound, the diisocyanate compound, and the styrene polymer into the solvent, as well as the mixing of mixture A and mixture B', can be performed using, for example, a mechanical stirrer or a magnetic stirrer. From the viewpoint of easily and uniformly mixing the components, the method using a mechanical stirrer is preferred.

[0363] By going through the steps (1) to (4), a mixture containing diurea, styrene polymer, solvent A and solvent B can be obtained.

[0364] (5) Remove solvent A and solvent B from the mixture obtained in step (4) above (S134).

[0365] This process can be performed in the same way as process (5) of manufacturing method A1.

[0366] (6) Next, the mixture remaining after removing solvent A and solvent B is washed (S135).

[0367] This cleaning process can remove unreacted amine compounds and diisocyanate compounds remaining in the mixture.

[0368] This process can be performed in the same way as process (6) of manufacturing method A1.

[0369] (7) The washed mixture is recovered to obtain a mixture C(S136) containing bisurea and styrene polymers.

[0370] If necessary, the resulting mixture C can be subjected to a pulverization process using bisurea. This pulverization process allows for the refinement and homogenization of the thickener.

[0371] In performing the above-mentioned pulverization process, from the viewpoint of being able to carry it out with a simple device and at low cost, it is preferable to use a small pulverizer (such as the one manufactured by Osaka Chemical Co., Ltd., or Labo Millser).

[0372] (8) Next, base oil is added to the mixture C containing diurea and styrene polymers, and the two are mixed (S137).

[0373] Specific examples of the base oils mentioned above are as described above.

[0374] The mixing of mixture C with the base oil can be carried out in the same manner as step (8) of manufacturing method A1.

[0375] By going through such a process, the aforementioned grease composition can also be manufactured.

[0376] [A variation of manufacturing method A]

[0377] In manufacturing methods A1 to A3, mixture C can be mixed with base oil, and then homogenized using a roller mill or the like as needed.

[0378] In addition, when manufacturing a grease composition that contains additives in addition to mixture C and base oil, for example, the necessary additives may be mixed after the base oil and mixture C are mixed, or mixture C and the necessary additives may be mixed simultaneously in the base oil.

[0379] (c) The order of the steps for removing solvent A and solvent B (S114, S124, S134) and the steps for cleaning the mixture (S115, S125, S135) can be reversed. In this case, for example, the following methods can be used.

[0380] The mixture of diurea dispersed in solvents A and B is placed in a separatory funnel. Water is then added to the separatory funnel, transferring unreacted amine and diisocyanate compounds to the aqueous phase. Next, the water containing the unreacted amine and diisocyanate compounds is removed from the separatory funnel. Then, solvents A and B are removed from the mixture after washing with the separatory funnel by steps (S114, S124, S134).

[0381] The steps for cleaning the mixture (S115, S125, S135) are not necessary and can be omitted.

[0382] The base oil can be added to the mixture obtained in the above-mentioned biuret synthesis process after the steps of synthesizing biuret (S113, S123, S133) and before the steps of removing solvent A and solvent B (S114, S124, S134). In this case, the steps of adding base oil to mixture C (S117, S127, S137) are not required.

[0383] Manufacturing method A, which includes the process of synthesizing diurea in the presence of styrene-based polymers, is suitable as a method for manufacturing grease compositions with good oil retention properties and capable of ensuring low torque.

[0384] (Manufacturing Method B)

[0385] As a specific implementation of manufacturing method B, manufacturing methods B1 to B3 can be exemplified, for example.

[0386] [Manufacturing Method B1]

[0387] Figure 10 This is a process diagram illustrating method B1 for manufacturing a lubricating grease composition.

[0388] (1) In manufacturing method B1, firstly, predetermined amounts of amine compound, diisocyanate compound, styrene polymer and base oil are prepared respectively.

[0389] Specific examples of amine compounds, diisocyanate compounds, styrene polymers, and base oils are as described above.

[0390] (2) Add a portion of the styrene polymer and an amine compound to half the amount of base oil to obtain mixture D(S211).

[0391] At this point, there are no particular restrictions on the timing of adding styrene polymers and amine compounds to the base oil.

[0392] (a) After mixing styrene polymers into the base oil, amine compounds can be further mixed in.

[0393] (b) Alternatively, amine compounds can be mixed into the base oil, followed by further mixing with styrene polymers.

[0394] (c) Alternatively, amine compounds and styrene polymers may be added to the base oil simultaneously, and then all components are mixed.

[0395] (3) Add the remaining styrene polymer and diisocyanate compound to the remaining base oil to obtain mixture E(S212).

[0396] At this point, there are no particular restrictions on the timing of adding styrene polymers and diisocyanate compounds to the base oil.

[0397] (a) After mixing styrene polymers into the base oil, diisocyanate compounds may be further mixed in.

[0398] (b) Alternatively, after mixing diisocyanate compounds into the base oil, styrene polymers may be further mixed in.

[0399] (c) Alternatively, diisocyanate compounds and styrene polymers may be added to the base oil simultaneously, and then all components are mixed.

[0400] (4) Mix the mixture D containing the amine compound and the mixture E containing the diisocyanate compound to react the amine compound with the diisocyanate compound to synthesize diurea (S213).

[0401] Here, mixture E can be added dropwise to mixture D while stirring mixture D to mix the two, or mixture D can be added dropwise to mixture E while stirring mixture E to mix the two.

[0402] The mixing of mixture D and mixture E can be carried out at room temperature or under heating.

[0403] When the process is carried out under heating, the heating temperature can be set to, for example, above 150°C and below 180°C.

[0404] Mixture D and mixture E are mixed in such a way that 2 to 2.2 moles of amine compound become 1 mole of diisocyanate compound.

[0405] There are no particular restrictions on the reaction time between the amine compound and the diisocyanate compound, as long as the reaction proceeds sufficiently. Specifically, for example, it can be set to be more than 0.5 hours and less than 2 hours.

[0406] In the processes described in (2) to (4) above, the mixing of the amine compound, diisocyanate compound, and styrene polymer into the base oil, as well as the mixing of mixture D and mixture E, can be performed using, for example, a mechanical stirrer or a magnetic stirrer. From the viewpoint of easily and uniformly mixing the components, the method using a mechanical stirrer is preferred.

[0407] By going through the processes of (1) to (4), it is possible to manufacture a grease composition containing diurea and styrene polymers in the base oil.

[0408] [Manufacturing Method B2]

[0409] Figure 11 This is a process diagram illustrating method B2 for manufacturing a lubricating grease composition.

[0410] (1) In manufacturing method B2, firstly, predetermined amounts of amine compound, diisocyanate compound, styrene polymer and base oil are prepared respectively.

[0411] Specific examples and preferred embodiments of amine compounds, diisocyanate compounds, styrene polymers and base oils are described above.

[0412] (2) Add an amine compound to half of the base oil to obtain mixture D'(S221).

[0413] (3) Add styrene polymers and diisocyanate compounds to the remaining base oil to obtain mixture E(S222).

[0414] At this point, there are no particular restrictions on the timing of adding styrene polymers and diisocyanate compounds to the base oil.

[0415] (a) After mixing styrene polymers into the base oil, diisocyanate compounds may be further mixed in.

[0416] (b) Alternatively, after mixing diisocyanate compounds into the base oil, styrene polymers may be further mixed in.

[0417] (c) Alternatively, diisocyanate compounds and styrene polymers may be added to the base oil simultaneously, and then all components are mixed.

[0418] (4) Mix the mixture D' containing the amine compound and the mixture E containing the diisocyanate compound to react the amine compound with the diisocyanate compound to synthesize diurea (S223).

[0419] This process can be carried out in the same way as process (4) of manufacturing method B1, except that the mixture D is changed to mixture D'.

[0420] In the processes described in (2) to (4) above, the mixing of the amine compound, diisocyanate compound, and styrene polymer into the base oil, as well as the mixing of mixture D' and mixture E, can be performed using, for example, a mechanical stirrer or a magnetic stirrer. From the viewpoint of easily and uniformly mixing the components, the method using a mechanical stirrer is preferred.

[0421] By going through the processes of (1) to (4), it is also possible to manufacture a grease composition containing diurea and styrene polymers in the base oil.

[0422] [Manufacturing Method B3]

[0423] Figure 12 This is a process diagram illustrating method B3 for manufacturing a lubricating grease composition.

[0424] (1) In manufacturing method B3, firstly, predetermined amounts of amine compound, diisocyanate compound, styrene polymer and base oil are prepared respectively.

[0425] Specific examples and preferred embodiments of amine compounds, diisocyanate compounds, styrene polymers and base oils are described above.

[0426] (2) Add styrene polymers and amine compounds to half the amount of base oil to obtain mixture D(S231).

[0427] At this point, there are no particular restrictions on the timing of adding styrene polymers and amine compounds to the base oil.

[0428] (a) After mixing styrene polymers into the base oil, amine compounds can be further mixed in.

[0429] (b) Alternatively, amine compounds can be mixed into the base oil, followed by further mixing with styrene polymers.

[0430] (c) Alternatively, amine compounds and styrene polymers may be added to the base oil simultaneously, and then all components are mixed.

[0431] (3) Add diisocyanate compound to the remaining base oil to obtain mixture E'(S232).

[0432] (4) Mix the mixture D containing the amine compound and the mixture E' containing the diisocyanate compound to react the amine compound with the diisocyanate compound to synthesize diurea (S233).

[0433] This process can be carried out in the same way as process (4) of manufacturing method B1, except that mixture E is changed to mixture E'.

[0434] In the processes described in (2) to (4) above, the mixing of the amine compound, diisocyanate compound, and styrene polymer into the base oil, as well as the mixing of mixture D and mixture E', can be performed using, for example, a mechanical stirrer or a magnetic stirrer. From the viewpoint of easily and uniformly mixing the components, the method using a mechanical stirrer is preferred.

[0435] By going through the processes of (1) to (4), it is also possible to manufacture a grease composition containing diurea and styrene polymers in the base oil.

[0436] [A variation of manufacturing method B]

[0437] In manufacturing methods B1 to B3, homogenization can be performed using a roller mill or similar equipment after the synthesis of diurea, as needed.

[0438] In addition, when manufacturing a grease composition that contains additives in addition to base oil, bisurea and styrene polymers, the necessary additives may be mixed in after the synthesis of bisurea.

[0439] In manufacturing method B1, the amount of styrene polymer incorporated in mixture D and the amount of styrene polymer incorporated in mixture E can be the same or different.

[0440] In manufacturing methods B1 to B3, the amount of base oil containing amine compounds and the amount of base oil containing isocyanate compounds can be different.

[0441] In steps (2) to (4) of manufacturing method B1, after preparing mixture D' which contains an amine compound and mixture E' which contains a diisocyanate compound in the base oil, mixture D', mixture E' and styrene polymer can be mixed.

[0442] Manufacturing method B, which includes the process of synthesizing diurea in the presence of styrene-based polymers, is also suitable as a method for manufacturing grease compositions with good oil retention properties and suitable for ensuring low torque.

[0443] Example

[0444] The invention described below will be further described in more detail based on the embodiments, but the invention described below is not limited to the embodiments.

[0445] The following raw materials were used in the examples / comparative examples.

[0446] ■ Diisocyanate compound: 4,4'-Diphenylmethane diisocyanate (MDI)

[0447] ■Amine compounds: Octylamine

[0448] ■Base oil: Poly-α-olefin: PAO8 (the dynamic viscosity of the base oil at 40℃ is 46 mm) 2 / Second)

[0449] ■ Solvent: Toluene

[0450] ■ Styrene-based polymers: Styrene-isoprene copolymer (manufactured by Lubrizol Corporation, Japan, Lubrizol 7306)

[0451] ■ Acrylic polymers: Alkyl methacrylate copolymers (manufactured by Sanyo Chemical Industries, Inc., ACLUBEV-1001)

[0452] (Example 1)

[0453] (1) The styrene-isoprene copolymer was dissolved in toluene. In addition, a predetermined amount of octylamine was mixed into the resulting solution to obtain mixture A1.

[0454] (2) Independent of the process in (1) above, a predetermined amount of MDI was mixed in a solution of styrene-isoprene copolymer dissolved in toluene to obtain mixture B1.

[0455] Here, the amount of styrene-isoprene copolymer added to obtain mixture A1 and the amount of styrene-isoprene copolymer added to obtain mixture B1 are set to be the same.

[0456] In steps (1) and (2), the amounts of the above-mentioned octylamine and the above-mentioned MDI are set as follows: the molar ratio of the two (octylamine:MDI) is 2:1 and the amount of the generated diurea is 40% by mass relative to 100% by mass of toluene.

[0457] In addition, the amount of styrene-isoprene copolymer added is set as follows: the amount of styrene-isoprene copolymer contained in the following mixture C of bisurea and styrene-isoprene copolymer is 7.00 by mass relative to the total amount of bisurea and styrene-isoprene copolymer.

[0458] The mixed solution A1 was prepared by adding styrene-isoprene copolymer and octylamine while stirring toluene with a mechanical stirrer.

[0459] In addition, mixture B1 is prepared by adding styrene-isoprene copolymer and MDI while stirring toluene using a mechanical stirrer.

[0460] (3) While stirring mixture A1 with a mechanical stirrer, mixture B1 is added dropwise to mixture A1 to mix the two.

[0461] After the addition of mixture B1 is completed, while stirring for another 0.5 hours, octylamine is reacted with MDI at room temperature to generate diurea.

[0462] (4) Then, the mixture containing diurea, styrene-isoprene copolymer and toluene was left at room temperature for 24 hours, and the toluene was evaporated to remove it, thus producing a mixture C (thickener) of diurea and styrene-isoprene copolymer.

[0463] (5) Add the room temperature mixture C to PAO8, which is the base oil, and heat to 150°C while stirring with a mechanical stirrer. Continue stirring with a mechanical stirrer for 30 minutes while maintaining the base oil containing mixture C at 170°C. Then, allow it to cool naturally to room temperature while continuing to stir with a mechanical stirrer, and stop stirring.

[0464] At this point, the amount of PAO8 (base oil) is set to 70.00% by mass relative to the total amount of PAO8 and mixture C.

[0465] Then, the mixture was homogenized using a roller mill to obtain a grease composition.

[0466] The biuret generated in this embodiment has the following structural formula.

[0467]

[0468] (Example 2)

[0469] The amount of styrene-isoprene copolymer added was varied such that the amount of styrene-isoprene copolymer contained in mixture C was 14.00% by mass relative to the total amount of bisurea and styrene-isoprene copolymer. Otherwise, a grease composition was obtained in the same manner as in Example 1.

[0470] (Comparative Example 1)

[0471] The amount of styrene-isoprene copolymer added was varied such that the amount of styrene-isoprene copolymer contained in mixture C was 1.00% by mass relative to the total amount of bisurea and styrene-isoprene copolymer. Otherwise, a grease composition was obtained in the same manner as in Example 1.

[0472] (Comparative Example 2)

[0473] (1) A predetermined amount of octylamine was mixed in toluene to obtain mixture A2.

[0474] (2) Independent of the process in (1) above, a predetermined amount of MDI was mixed in toluene to obtain mixture B2.

[0475] In steps (1) and (2), the amounts of the above-mentioned octylamine and the above-mentioned MDI are set as follows: the ratio of the two (octylamine:MDI) is 2:1 in molar ratio, and the amount of the generated diurea is 40% by mass relative to 100% by mass of toluene.

[0476] Mixture A2 was prepared by adding octylamine while stirring toluene using a mechanical stirrer.

[0477] In addition, mixture B1 was prepared by adding MDI while stirring toluene using a mechanical stirrer.

[0478] (3) While stirring mixture A2 with a mechanical stirrer, add mixture B2 dropwise to mixture A2 to mix the two.

[0479] After the addition of mixture B2 was completed, while stirring continued for 0.5 hours, octylamine was allowed to react with MDI at room temperature to generate diurea.

[0480] (4) Then, the mixture containing diurea and toluene was left at room temperature for 24 hours to evaporate and remove the toluene, thus producing diurea (thickener).

[0481] (5) Add the room-temperature diurea obtained in (4) to PAO8, which is used as a base oil at room temperature, and heat to 150°C while stirring with a mechanical stirrer. Continue stirring with a mechanical stirrer for 30 minutes while keeping the base oil mixed with diurea at 170°C. Then, while continuing to stir with a mechanical stirrer, allow it to cool naturally to room temperature and stop stirring.

[0482] At this point, the amount of PAO8 (base oil) is set to 70.00% by mass relative to the total amount of PAO8 and mixture C.

[0483] Then, the mixture was homogenized using a roller mill to obtain a grease composition.

[0484] The structure of the diurea generated in Comparative Example 2 is the same as that in Example 1.

[0485] The grease composition manufactured in Comparative Example 2 does not contain styrene-isoprene copolymer.

[0486] (Comparative Example 3)

[0487] The grease composition was obtained in the same manner as in Example 1, except that an acrylic polymer (alkyl methacrylate copolymer) was used instead of a styrene-isoprene copolymer.

[0488] (Comparative Example 4)

[0489] (1) Diurea was manufactured in the same manner as in (1) to (4) of Comparative Example 2.

[0490] (2) Styrene-isoprene copolymer and the room-temperature diurea obtained in (1) were added to PAO8 (room temperature) as base oil, and heated to 150°C while stirring with a mechanical stirrer. The base oil containing the styrene-isoprene copolymer and diurea was kept at 170°C and stirred with a mechanical stirrer for 30 minutes. Then, while continuing to stir with a mechanical stirrer, the mixture was allowed to cool naturally to room temperature and stirring was stopped.

[0491] At this point, the amount of PAO8 (base oil) is set to 70.00% by mass relative to the total amount of PAO8, styrene-isoprene copolymer and diurea.

[0492] In addition, the amount of styrene-isoprene copolymer is set to be 7.00% by mass relative to the total amount of styrene-isoprene copolymer and diurea.

[0493] Then, the mixture was homogenized using a roller mill to obtain a grease composition.

[0494] (Example 3)

[0495] (1) Use PAO8 as the base oil and preheat the base oil to 100°C.

[0496] (2) Weigh the base oil, styrene-isoprene copolymer, octylamine and 4,4'-diphenylmethane diisocyanate (MDI). The amounts of the above octylamine and the above MDI are weighed in a molar ratio of 2:1 (octylamine:MDI).

[0497] Here, the amount of base oil is set to be 85.00% by mass relative to the total amount of PAO8 and thickener (styrene-isoprene copolymer and diurea generated through subsequent processes).

[0498] In addition, the amount of styrene-isoprene copolymer was set to 7.00% by mass relative to the total amount of styrene-isoprene copolymer and the generated diurea.

[0499] (3) Half the amount of base oil (100℃), half the amount of styrene-isoprene copolymer and octylamine were added to stainless steel container A and stirred at 100℃ for 30 minutes to obtain mixture D1.

[0500] (4) Add the remaining half of the base oil (100°C), the remaining half of the styrene-isoprene copolymer and MDI to another stainless steel container B, and stir at 100°C for 30 minutes to obtain mixture E1.

[0501] (5) Add the mixture D1 containing octylamine in stainless steel container A to stainless steel container B, and slowly add it to the mixture E1 containing MDI.

[0502] (6) After confirming that all the mixture D1 in stainless steel container A has been put into stainless steel container B, the temperature is raised to 170°C.

[0503] (7) Stir while heating and keep the temperature at 170°C for 30 minutes.

[0504] (8) Stop heating and let it cool naturally while stirring until it reaches 100°C.

[0505] (9) After confirming that the temperature is below 100°C, stop stirring and allow it to cool naturally to room temperature.

[0506] (10) Homogenization was carried out using a roller mill to obtain a grease composition.

[0507] (Comparative Example 5)

[0508] (1) Use PAO8 as the base oil and preheat the base oil to 100°C.

[0509] (2) Weigh the base oil, octylamine and 4,4'-diphenylmethane diisocyanate (MDI). The amounts of the above octylamine and the above MDI are weighed in a molar ratio of 2:1 (octylamine:MDI).

[0510] Here, the amount of base oil is set to be 85.00% by mass relative to the total amount of PAO8 and thickener (diurea generated through subsequent processes).

[0511] (3) Add half the amount of base oil (100℃) and octylamine to stainless steel container A, and stir at 100℃ for 30 minutes to obtain mixture D2.

[0512] (4) Add the remaining half of the base oil (100°C) and MDI to another stainless steel container B, and stir at 100°C for 30 minutes to obtain mixture E2.

[0513] (5) Add the mixture D2 containing octylamine in stainless steel container A to stainless steel container B, and slowly add it to the mixture E2 containing MDI.

[0514] (6) After confirming that all the mixture D2 in stainless steel container A has been put into stainless steel container B, the temperature is raised to 170°C.

[0515] (7) Stir while heating and keep the temperature at 170°C for 30 minutes.

[0516] (8) Stop heating and let it cool naturally while stirring until it reaches 100°C.

[0517] (9) After confirming that the temperature is below 100°C, stop stirring and allow it to cool naturally to room temperature.

[0518] (10) Homogenization was carried out using a roller mill to obtain a grease composition.

[0519] The grease composition manufactured in Comparative Example 5 does not contain styrene-isoprene copolymer.

[0520] (Comparative Example 6)

[0521] (1) A composition containing base oil and diurea was obtained in the same manner as in (1) to (9) of Comparative Example 5.

[0522] (2) Add the styrene-isoprene copolymer dissolved in the solvent (toluene) to the composition obtained in (1) and stir for 30 minutes at room temperature.

[0523] At this point, the amount of styrene-isoprene copolymer is set to 7.00% by mass relative to the total amount of styrene-isoprene copolymer and diurea.

[0524] (3) Stir while heating and keep the temperature at 100°C for 30 minutes to allow the toluene to evaporate and be removed.

[0525] Then, the mixture was homogenized using a roller mill to obtain a grease composition.

[0526] The grease compositions prepared in the Examples and Comparative Examples were evaluated as follows. The results are shown in Table 3.

[0527] 1. Mixed consistency (60W)

[0528] For the grease compositions manufactured in the examples and comparative examples, the mixture consistency (60W) was determined by a method based on JIS K2220.

[0529] 2. Oil separation degree

[0530] For the grease compositions manufactured in the examples and comparative examples (other than the grease compositions of Comparative Examples 4 and 6), the oil separation degree was determined by a method based on JIS K 2220 11. The results are shown in Table 1.

[0531] At this point, the sample size was set to 10g, the test temperature to 150℃, and the test time to 24 hours. The number of samples was set to 2, and the average value was used as the evaluation result.

[0532] 3. Bearing rotational torque

[0533] The bearing rotation torque of the grease compositions prepared in the examples and comparative examples (other than the grease compositions of comparative examples 3, 4 and 6) was determined using a rotation torque testing machine according to the conditions in Table 1 below.

[0534] Here, the grease composition prepared in the examples and comparative examples was sealed into the 62022RUCM (with non-contact seals on both sides) used as test bearings, in such a way that the volume of the grease composition was 35% by volume relative to the volume of the space after removing the balls and the retainer from the space enclosed by the inner ring, outer ring and seal.

[0535] The test bearing was assembled in the testing machine and tested for 1800 minutes. -1 Rotate for 30 minutes, and take the average torque in the last minute as the bearing rotation torque. Set the sample size to 2, and take the average value as the evaluation result.

[0536] It should be noted that in this evaluation, if the rotational torque is below 12 mN·m, it is considered to have good low torque performance, and if the rotational torque is below 10 mN·m, it is considered to have even better low torque performance.

[0537] [Table 1]

[0538]

[0539] 4. Determination of the average particle size of thickeners

[0540] The average particle size of the thickener contained in the grease compositions prepared in the examples and comparative examples was determined using a confocal laser microscope (manufactured by Leica Microsystems, TCS SP08). The confocal laser microscope was configured as shown in Table 2.

[0541] The device incorporates software (Leica Application Suite X (LAS X) Version 4.4.0) capable of calculating the average particle size of the observed material. When using this software, the volume of the thickener can be calculated for each particle from the acquired 3D image, the particle diameter can be calculated by assuming the shape of each particle to be a perfect sphere, and the average diameter of each particle can be used as the measured value (average particle size).

[0542] The average diameter of the obtained thickeners is shown in Table 3.

[0543]

[0544] As shown in Table 3, the average diameter of particles with a diameter of 0.2 μm or more in the thickener contained in the grease composition according to the embodiments of this disclosure is 0.2 μm or more and 1.0 μm or less. Furthermore, it is confirmed that the above-mentioned grease composition has a low oil separation degree (0.2% or less) and good oil retention properties. Additionally, it is confirmed that the above-mentioned grease composition has good low torque properties.

[0545] Symbol Explanation

[0546] 1: Dual pinion type electric power steering system; 2: Steering shaft; 3: Steering gear assembly; 33: Housing

[0547] 31: Rack shaft; 310: First rack tooth portion; 311: First rack tooth; 312: Cylindrical surface; 313: Cylindrical surface; 314: Second rack tooth portion; 315: Second rack tooth.

[0548] 32: First pinion shaft; 320: First pinion tooth; 321: First pinion tooth; 392: First component piece.

[0549] 54: Second pinion shaft; 540: Second pinion tooth; 541: Second pinion tooth; 592: Second component.

[0550] 601: Column-type electric power steering system; 602: Steering shaft; 603: Steering gear assembly; 633: Housing

[0551] 631: rack shaft, 710: rack teeth, 711: rack teeth, 712: cylindrical surface

[0552] 632: Pinion shaft, 720: Pinion teeth, 721: Pinion teeth, 792: Plate component

[0553] 801: Ball bearing; 802: Inner ring; 803: Outer ring; 804: Ball; 805: Retainer; 806: Seal.

[0554] G grease composition

Claims

1. A method for manufacturing a lubricating grease composition, wherein, Prepare: Styrene polymers, amine compounds, Isocyanate compounds, lubricating oil, The first solvent that does not dissolve the generated urea compound, and The second solvent 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, thereby preparing 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 to react the amine compound and the isocyanate compound, thereby generating a third mixture containing the styrene polymer and the urea compound. The first solvent and the second solvent are removed from the third mixture, and then the lubricating oil is added, wherein 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 urea compound and the styrene polymer.

Images