Grease composition, pivot assembly bearing, and bearing apparatus including the bearing

Patent metadata

Field	Value
Publication number	US-12534680-B2
Application number	US-202218703861-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

Object
Objective is to provide a grease composition for a pivot assembly and a pivot assembly bearing filled with the grease composition, and to provide a bearing apparatus as well as a drive apparatus including the bearing apparatus, which is capable of suppressing adhesion of a volatilized component to a magnetic disk or the like even when the grease composition is volatilized by application of the grease composition and the bearing, thereby suppressing occurrence of read/write errors of an HDD.
Solution
Provided are: a grease composition for a pivot assembly bearing including an aromatic ester-based base oil and a thickener, the aromatic ester-based base oil containing an aromatic ester compound having an ester group *—(CO)O— as a substituent on a ring, where * is a bonding site to an aromatic ring, and having an alkyl group with a total of 8 or more carbon atoms bonded to an oxygen atom of the ester group; a pivot assembly bearing filled with the grease composition for pivot assembly bearing; a bearing apparatus including the pivot assembly bearing; and a disk drive apparatus equipped with the bearing apparatus.

First claim

The invention claimed is:

1 . A grease composition for a pivot assembly bearing, comprising an aromatic ester-based base oil and a thickener,
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 an 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 for a pivot assembly bearing comprises a urea-based thickener as a 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, 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° of from 200 to 270 mm 2 /mg.

2 . The grease composition for a pivot assembly bearing according to claim 1 , further comprising a phenol-based antioxidant as an antioxidant.

3 . The grease composition for a pivot assembly bearing according to claim 2 , wherein the phenol-based antioxidant is a hindered phenol-based antioxidant.

4 . The grease composition for a pivot assembly bearing according to claim 3 , wherein the hindered phenol-based antioxidant is at least one selected from the group consisting of:
octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate; 2,4-bis-(n-octylthio)-6-(4-hydroxy-3,5-di-t-butylanilino)-1,3,5-triazine; triethyleneglycol-bis[3-(3-t-butyl-5-methyl-4-hydroxyphenyl)propionate]; 2,2-thio-diethylenebis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate]; and octyl-3,5-di-tert-butyl-4-hydroxy-hydrocinnamic acid.

5 . The grease composition for a pivot assembly bearing according to claim 1 , further comprising a diarylamine-based antioxidant as an antioxidant.

6 . The grease composition for a pivot assembly bearing according to claim 5 , wherein the diarylamine-based antioxidant is at least one selected from the group consisting of diphenylamine, alkylated diphenylamine, and alkylated phenyl-α-naphthylamine.

7 . The grease composition for a pivot assembly bearing according to claim 1 , further comprising a phosphate ester-based compound as an extreme pressure additive.

8 . The grease composition for a pivot assembly bearing according to claim 7 , wherein the phosphate ester-based compound is at least one compound selected from the group consisting of phosphate triester, phosphate monoester, and phosphate diester.

9 . The grease composition for a pivot assembly bearing according to claim 8 , wherein the phosphate ester-based compound is at least one selected from the group consisting of: tricresyl phosphate (CAS No. 1330-78-5); triphenyl phosphate; tributyl phosphate; trioctyl phosphate; trioleyl phosphate; 2-ethylhexyl acid phosphate (CAS No. 12645-31-7); alkyl (C12, C14, C16, C18) acid phosphate; isotridecyl acid phosphate (CAS No. 52933-07-0); and oleyl acid phosphate (CAS No. 37310-83-1).

10 . A pivot assembly bearing filled with the grease composition for a pivot assembly bearing according to claim 1 .

11 . A bearing apparatus, comprising the pivot assembly bearing according to 10 .

12 . A disk drive apparatus, comprising the bearing apparatus according to claim 11 .

13 . The disk drive apparatus according to claim 12 , comprising 9 or more disks having a diameter of 3.5 inches.

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

15 . The disk drive apparatus according to claim 12 , wherein the disk drive apparatus employs a heat-assisted magnetic recording system.

16 . The grease composition for a pivot assembly 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.

17 . The grease composition for a pivot assembly bearing according to claim 16 , wherein the aromatic ester-based base oil is the aromatic ester compound (B) or (C).

18 . The grease composition for a pivot assembly 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) 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

 and;
(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.

19 . The grease composition for a pivot assembly bearing according to claim 18 , wherein the aromatic ester-based base oil is the aromatic ester compound of (b) or (d).

20 . The grease composition for a pivot assembly 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.

Assignees

• Minebea Mitsumi Inc

Inventors

• Tsuna Motojiro
• Hatcho Jun
• Shingai Takanori

Classifications

• G11B2005/0021

  Thermally assisted recording using an auxiliary energy source for heating the recording layer locally to assist the magnetization reversal · CPC title

• C10N2050/10

  semi-solid; greasy · CPC title

• C10N2040/02

  Bearings · CPC title

• C10N2030/10

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

• C10N2030/06

  Oiliness; Film-strength; Anti-wear; Resistance to extreme pressure · CPC title