Rolling bearing, pivot assembly bearing, and disk drive apparatus

Patent metadata

Field	Value
Publication number	US-12534681-B2
Application number	US-202218704114-A
Country	US
Kind code	B2
Filing date	Oct 25, 2022
Priority date	Oct 25, 2021
Publication date	Jan 27, 2026
Grant date	Jan 27, 2026

Abstract

The application provides a rolling bearing including a grease composition, the grease composition containing a base oil and a thickener, the base oil containing an aromatic ester-based base oil, and the thickener containing a urea-based thickener, where the grease composition has a storage elastic modulus at 25° C. of from 1200 to 3000 Pa as measured under conditions of a film thickness of 1 mm and a shear strain of 1% and has an oil separation amount at 80° C. of from 200 to 270 mm 2 /mg; a pivot assembly bearing apparatus including the rolling bearing; and a disk drive apparatus including the pivot assembly bearing apparatus.

First claim

The invention claimed is:

1 . A rolling bearing, comprising:
an inner ring; an outer ring disposed coaxially with the inner ring at an outer peripheral side of the inner ring; a plurality of rolling elements disposed between the inner ring and the outer ring; a retainer retaining the rolling elements; and a grease composition retained between the inner ring and the outer ring, the grease composition comprising an aromatic ester-based base oil and a thickener, the thickener comprising a urea-based thickener, the urea-based thickener comprising a diurea compound represented by Formula (1):
R 1 —NHCONH—R 2 —HNOCHN—R 3   Formula (1)

where in Formula (1), R 1 and R 3 are monovalent alicyclic hydrocarbon groups or monovalent aliphatic hydrocarbon groups, and a molar ratio of the alicyclic hydrocarbon group to the aliphatic hydrocarbon group is from 6:4 to 8:2, and R 2 represents a divalent aromatic hydrocarbon group,
the aromatic ester-based base oil comprises an aromatic ester compound having an ester group *—C(═O)O— as a substituent on an aromatic ring, where * is a bonding site to the aromatic ring, and having an alkyl group with a total of 8 or more carbon atoms bonded to the oxygen atom of the ester group, and
the alkyl group is selected from the group consisting of:
a branched alkyl group formed with a branched chain bonded to a linear alkyl group with 8 or more and 11 or less carbon atoms, and
a branched alkyl group formed with two or more branched chains bonded to a linear alkyl group with 6 or more and 11 or less carbon atoms,
wherein the grease composition has:
a storage elastic modulus at 25° C. of from 1200 to 3000 Pa as measured under conditions of a film thickness of 1 mm and a shear strain of 1%, and
an oil separation amount at 80° C. of from 200 to 270 mm 2 /mg.

2 . The rolling bearing according to claim 1 , wherein
the aromatic ester-based base oil has a kinematic viscosity at 40° C. of from 40 to 150 mm 2 /s.

3 . The rolling bearing according to claim 2 ,
wherein the aromatic ester-based base oil has a kinematic viscosity at 40° C. of from 50 to 80 mm 2 /s.

4 . The rolling bearing according to claim 1 ,
wherein the grease composition further comprises a phenol-based antioxidant.

5 . The rolling bearing according to claim 1 ,
wherein the grease composition further comprises a diarylamine-based antioxidant.

6 . The rolling bearing according to claim 1 ,
wherein the grease composition further comprises a phosphate ester-based extreme pressure additive.

7 . The rolling bearing according to claim 1 ,
wherein the grease composition comprises the thickener in a proportion of from 10 mass % to 13 mass % based on a total mass of the grease composition.

8 . The rolling bearing according to claim 1 ,
wherein the grease composition has a worked penetration of from 260 to 300.

9 . A pivot assembly bearing apparatus, comprising the rolling bearing according to claim 1 .

10 . A disk drive apparatus, comprising the pivot assembly bearing apparatus according to claim 9 .

11 . The disk drive apparatus according to claim 10 , comprising 9 or more disks having a diameter of 3.5 inches.

12 . The disk drive apparatus according to claim 10 , wherein an internal space is filled with a gas having a density lower than air.

13 . The disk drive apparatus according to claim 10 , wherein the disk drive apparatus employs a heat-assisted magnetic recording system.

14 . The rolling bearing according to claim 1 , wherein the aromatic ester-based base oil is an aromatic ester compound selected from the group consisting of:
(A) an aromatic ester compound in which a branched alkyl group having a total of 11 carbon atoms is bonded to an oxygen atom of the ester group; (B) an aromatic ester compound in which a branched alkyl group having a total number of carbon atoms of 11 and a linear alkyl group having a total number of carbon atoms of 11 are bonded to an oxygen atom of the ester group; and (C) an aromatic ester compound in which a branched alkyl group having a total of 11 carbon atoms and a linear alkyl group having a total of 10 carbon atoms are bonded to an oxygen atom of the ester group.

15 . The rolling bearing according to claim 14 , wherein the aromatic ester-based base oil is the aromatic ester compound (B) or (C).

16 . The rolling bearing according to claim 1 , wherein the aromatic ester-based base oil is an aromatic ester compound selected from the group consisting of:
(a) an aromatic ester compound having a branched alkyl group having a total of 11 carbon atoms represented by the following formula (K) [Chemical formula 1] wherein group R of the formula (K) is represented by the following formula:

(b) a triester compound of trimellitic acid and a mixture of an alcohol in which a hydroxy group is bonded to a linear alkyl group having 11 carbon atoms and an alcohol in which a hydroxy group is bonded to a branched alkyl group having a total of 11 carbon atoms represented by the following group R
[Chemical formula 2]

(d) a triester compound of trimellitic acid and a mixture of an alcohol in which a hydroxy group is bonded to a linear alkyl group having 10 carbon atoms and an alcohol in which a hydroxy group is bonded to a branched alkyl group having a total of 11 carbon atoms represented by the group R.

17 . The rolling bearing according to claim 16 , wherein the aromatic ester-based base oil is the aromatic ester compound of (b) or (d).

Assignees

• Minebea Mitsumi Inc

Inventors

• Tsuna Motojiro
• Shingai Takanori

Classifications

• C10N2050/10

  semi-solid; greasy · CPC title

• C10N2040/02

  Bearings · CPC title

• C10N2030/10

  Inhibition of oxidation, e.g. anti-oxidants · CPC title

• C10N2030/08

  Resistance to extreme temperature · CPC title

• C10N2020/071

  Branched chain compounds · CPC title