Charge control agent for fluid dynamic bearing motor lubricant
Embodiments disclosed herein generally relate to magnetic recording systems having a spindle motor and, more particularly, to an optimized lubricant for bearings within the spindle motor. A lubricant used in a fluid dynamic bearing motor has an antioxidant additive and a charge control agent dissolved in a diester base oil. The charge control agent is chemically attached to the same diacid reactant used in the diester lubricant base oil, and is prepared through an esterification reaction. The charge control agent is then dissolved in the lubricant base oil. The charge control agent is soluble in the lubricant, and is resistant to free radical oxidation. The charge control agent effectively controls the charge of the lubricant by creating electron donor/acceptor sites in the lubricant, facilitating an independent electronic pathway through the lubricant.
1. A fluid dynamic bearing motor, comprising:
a slider bearing coupled to the fluid dynamic bearing motor;
a central axis;
a spindle shaft coaxial with the central axis;
one or more bearings adjacent the shaft;
a lubricant disposed between the one or more bearings and the shaft, wherein the lubricant includes a soluble charge control agent chemically attached thereto, wherein the lubricant has an antioxidant additive, and wherein each of the lubricant and the charge control agent include an acid reactant, the acid reactant being the same for the lubricant and the charge control agent.
2. The fluid dynamic bearing motor of claim 1 , wherein the acid reactant is sebacic acid.
3. The fluid dynamic bearing motor of claim 2 , wherein the soluble charge control agent is chemically attached to the lubricant through an esterification reaction.
4. The fluid dynamic bearing motor of claim 3 , wherein the soluble charge control agent is dibenzyl sebacate.
5. The fluid dynamic bearing motor of claim 4 , wherein one reactant used in the esterification reaction is benzyl alcohol.
6. The fluid dynamic bearing motor of claim 3 , wherein the soluble charge control agent is dinaphthyl sebacate.
7. The fluid dynamic bearing motor of claim 6 , wherein one reactant used in the esterification reaction is naphthyl alcohol.
8. The fluid dynamic bearing motor of claim 3 , wherein one reactant used in the esterification reaction is anthracene methanol.
9. The fluid dynamic bearing motor of claim 3 , wherein one reactant used in the esterification reaction is pyrene methanol.
10. The fluid dynamic bearing motor of claim 1 , wherein the soluble charge control agent is an asymmetric aryl ester.
11. The fluid dynamic bearing motor of claim 1 , wherein the acid reactant is a poly-acid.
12. The fluid dynamic bearing motor of claim 1 , wherein the acid reactant is a mono-acid.
13. A magnetic recording system, comprising:
an actuator;
an actuator arm coupled to the actuator;
a spindle disposed below the actuator arm;
one or more magnetic media disposed on the spindle;
a fluid dynamic bearing motor coupled to the spindle and adapted to actuate the spindle, the fluid bearing motor further comprising:
a central axis;
a spindle shaft coaxial with the central axis;
one or more bearings adjacent the shaft;
a lubricant disposed between the one or more bearings and the shaft, wherein the lubricant includes a soluble charge control agent chemically attached thereto, wherein the lubricant has an antioxidant additive, and wherein each of the lubricant and the charge control agent include an acid reactant, the acid reactant being the same for the lubricant and the charge control agent.
14. The magnetic recording system of claim 13 , wherein the magnetic recording system is a hard disk drive, the hard disk drive further comprising a slider coupled to the actuator arm and a read/write head coupled to the slider.
15. The magnetic recording system of claim 13 , wherein the acid reactant is sebacic acid.
16. The magnetic recording system of claim 15 , wherein the soluble charge control agent is chemically attached to the lubricant through an esterification reaction.
17. The magnetic recording system of claim 16 , wherein the soluble charge control agent is dibenzyl sebacate.
18. The magnetic recording system of claim 17 , wherein one reactant used in the esterification reaction is benzyl alcohol.
19. The magnetic recording system of claim 16 , wherein the soluble charge control agent is dinaphthyl sebacate, and wherein one reactant used in the esterification reaction is naphthyl alcohol.
20. The magnetic recording system of claim 13 , wherein the relative permittivity of the lubricant and soluble charge control agent solution is between about 2.5 and 200.
21. The magnetic recording system of claim 13 , wherein the conductivity of the lubricant and soluble charge control agent solution is between about 1 and 100 nS/m.
22. The magnetic recording system of claim 13 , wherein the soluble charge control agent is an aryl ester, the concentration of the aryl ester charge control agent being 0.1 to 10% by weight.
23. The magnetic recording system of claim 13 , wherein the soluble charge control agent is an asymmetric aryl ester or an asymmetric alkyl ester that is liquid at room temperature, and wherein the asymmetric aryl ester or asymmetric alkyl ester is used as a base oil of the lubricant with a concentration of 90 to 100% by weight.