Patent Application
20080144219
1. Field of the Invention
Embodiments of the present invention generally relate to perfluoropolyether (PFPE) lubricants, and more specifically to increasing the conductivity of PFPE lubricants.
2. Description of the Related Art
Nearly every kind of computer today, be it a desktop computer, server, mainframe or supercomputer contains at least one hard disk drive (HDD). In fact, many modern electronic devices, such as camcorders and VCRs incorporate hard disk drives. The advantage of including hard disk drives is that they can store large amounts of information including the programs and data required to operate and use computers and electronic devices.
A hard disk drive comprises several mechanical components such as magnetic disks, motors, actuator arms and electromagnetic heads to read and write data. A magnetic disk may contain concentric data tracks containing the data stored on the disks. The actuator arm may be coupled with an electromagnetic head. The electromagnetic head may be placed on a track of an associated disk to perform read and write operations. Motors may rotate the magnetic disks or move the actuator arms to place a head at a particular location on a disk to facilitate reading and writing data to the magnetic disk.
Lubricants may be applied to various components in a hard disk drive to reduce friction between moving parts, thereby reducing wear and tear of the parts. For example, lubricants may be used on the surface of magnetic disks to reduce friction at the head/disk interface and in components of a fluid dynamic bearings (FDB) motor. In some cases, it may be desirable to apply conductive lubricants to HDD components. For example, lubricants used in a FDB motor are generally required to be conductive to allow dissipation of undesired charge build-up on magnetic disks.
Perfluoropolyether (PFPE) lubricants are commonly used on several HDD components. PFPEs are a family of fluorinated synthetic fluids that are used to formulate lubricants that function for long periods of time in extreme environments. PFPE's are long chain fluoropolymers that are slippery and wet surfaces well, thereby making excellent lubricants. Moreover, PFPE's such as Ausimont Fomblin Z-DOL, Z-Tetraol, AM2001 and AM3001 are widely used for several disk drive applications such as magnetic disk lubrication.
However, one problem with PFPE lubricants is that it has poor conductivity. Furthermore, low polarity of the fluorinated PFPE lubricants leads to poor solubility and/or affinity with most additives. Therefore, tailoring the conductivity of PFPE lubricants has proven to be problematic because conductive additives, which are typically polar species, are immiscible with PFPE lubricants.
Accordingly, there is a need for methods to tailor the conductivity of PFPE lubricants.
The present invention generally relates to perfluoropolyether (PFPE) lubricants, and more specifically to increasing the conductivity of PFPE lubricants.
One embodiment of the invention provides a method for increasing the conductivity of a perfluoropolyether (PFPE) lubricant. The method generally comprises dissolving a predetermined amount of the PFPE lubricant in a solvent, dissolving a predetermined amount of a hydrophobic ionic liquid in the solvent, and evaporating at least some of the solvent, thereby leaving a mixture of the PFPE lubricant and the hydrophobic ionic liquid, wherein the hydrophobic ionic liquid increases the conductivity of the PFPE lubricant.
Another embodiment of the invention provides a hard disk drive generally comprising one or more magnetic disks and a FDB motor configured to rotate the one or more magnetic disks, wherein the FDB motor is lubricated with a conductive PFPE lubricant, the conductive PFPE lubricant comprising a mixture of a PFPE lubricant and a hydrophobic ionic liquid.
Yet another embodiment of the invention provides a lubricant generally comprising a PFPE lubricant and a hydrophobic ionic liquid dissolved in the PFPE lubricant, wherein the hydrophobic ionic liquid is selected to increase the conductivity of the lubricant.
So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings.
It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.
Embodiments of the invention generally relate to PFPE lubricants, and more specifically to increasing the conductivity of PFPE lubricants. PFPE lubricants generally have low polarity and do not dissolve most conductive additives that tend to be highly polar. However, hydrophobic ionic liquids are highly fluorinated and have low polarity. Therefore, the hydrophobic ionic liquids may be dissolved in a PFPE lubricant to increase the conductivity of the PFPE lubricant.
In the following, reference is made to embodiments of the invention. However, it should be understood that the invention is not limited to specific described embodiments. Instead, any combination of the following features and elements, whether related to different embodiments or not, is contemplated to implement and practice the invention. Furthermore, in various embodiments the invention provides numerous advantages over the prior art. However, although embodiments of the invention may achieve advantages over other possible solutions and/or over the prior art, whether or not a particular advantage is achieved by a given embodiment is not limiting of the invention. Thus, the following aspects, features, embodiments and advantages are merely illustrative and, unless explicitly present, are not considered elements or limitations of the appended claims.
A top clamp 170 may be placed at the tip end of the spindle motor, as illustrated in
Magnetic disks 110 may contain circular tracks of data on both the top and bottom surfaces of the disk. An electromagnetic head, for example head 180, may be positioned on a track. As each disk spins, data may be written and read from the data track. Electromagnetic head 180 may be coupled to an actuator arm 130 as illustrated in
As described above, a plurality of magnetic disks may be stacked vertically in HDD 100. Each disk may have read and write tracks on each side of the disk. Therefore, electromagnetic heads may be placed on both sides of the disk.
Actuator arm 204 may contain head 205. Head 205 may be configured to access data tracks on the bottom face of disk 201 and on the top face of disk 202. While two magnetic disks are illustrated in
Referring back to
Spindle motor 140 may be configured to rotate the magnetic disks at a predetermined rate. For example, the spindle motor 140 may be configured to spin at a rate of 10,000 revolutions per minute (rpm). One skilled in the art will recognize however, that any reasonable spin rate may be employed. The spin rate for example may depend on the type of disk drive, the type of computer, etc.
Spindle motor 140 may include a rod like axle (spindle) inside the hard drive. The magnetic disks 110 may be center-mounted on the spindle, and the spindle motor may rotate the spindle and the magnetic disks 110. In one embodiment of the invention, spindle motor 140 may be a fluid dynamic bearing (FDB) motor. In other words, spindle motor 140 may use fluid as a bearing to rotate the spindle inside a sleeve of the spindle motor.
In one embodiment of the invention, lubricants placed in the spacing 330 may be conductive. Therefore, the lubricant may facilitate discharges of undesired charge build up on the magnetic disks 110. In other words, undesired charge build up on magnetic disks 110 connected to spindle 310 may dissipate into the body of spindle motor 300 through the conductive lubricant placed in the spacing 330.
In one embodiment of the invention, the lubricant used in spacing 330 may be a PFPE based lubricant. In one embodiment of the invention, the PFPE lubricants may belong to the perfluoropolyoxyalkane family, for example, Z-Dol and Z-Dol-4000 such as that available from Solvay Solexis, Inc. Alternatively, Z-Tetraol such as that available from Solvay Solexis, Inc, or a Cyclotriphosphazene-Terminated Perfluoropolyether lubricant such as A20H available from Matsumura Oil Research Corporation may be used. In one embodiment, one or more of the PFPE lubricants may be mixed, for example, ZDol/A20H.
PFPE lubricants may provide several advantages over other lubricants, for example, higher thermal and chemical stability than conventional lubricants. However, because PFPE lubricants have poor conductivity, the PFPE lubricants must be altered to make them more conductive. The following section describes methods for tailoring the conductivity of PFPE lubricants.
In one embodiment of the invention, increasing conductivity of PFPE lubricants may involve dissolving a predetermined amount of ionic liquid in the PFPE lubricant. Ionic liquids are materials that may be composed substantially of anions and cations. An anion is a negatively charged particle and a cation is a positively charged particle. Ionic liquids may provide several advantages such as thermal stability, electric conductivity, non-flammability, and the like.
In one embodiment of the invention, a small amount of a “hydrophobic ionic liquid” such as that available from Covalent Associates, Inc. may be dissolved into a PFPE lubricant to increase conductivity of the PFPE lubricant. Hydrophobic ionic liquids have a wide liquidus range and offer advantages of low volatility, high thermochemical and electrochemical stability, and low sensitivity to oxidation. Furthermore, hydrophobic ionic liquids are highly fluorinated and therefore have significant solubility in the non-polar PFPE disk lubricants. Exemplary hydrophobic ionic liquids include, for example, 1-Ethyl-3-methylimidazolium bis(pentafluoroethylsulfonyl)-imide (hereinafter referred to as EMIBeti) available from Covalent Associates, Inc.
Dissolving a hydrophobic ionic liquid in a PFPE lubricant may involve dissolving both the PFPE lubricant and the hydrophobic ionic liquid in a solvent.
Column 580 of
A conductive PFPE lubricant may offer several advantages. As described earlier, a FDB motor generally requires conductive lubricants that operate as a bearing in a sleeve containing the spindle. The conductive PFPE lubricant may be used as the lubricant in the FDB motor in, for example, space 330 of
Conductive PFPE lubricants may also be used to lubricate the surface of magnetic disks. As discussed above, one common problem with lubricants on the magnetic disk surface is the unwanted buildup of charge on the magnetic disk surface. The unwanted buildup of charge on the magnetic disk surface may occur due to the motion of the head over a magnetic disk surface or a discharge of charged particles from the head to the magnetic disk.
The presence of static charge on the magnetic disk surface may cause the lubricant to degrade and/or accumulate in particular areas of the magnetic disk surface. This may increase the risk of damage to the magnetic disk surface. Furthermore, if the head passes over a region where lubricant has collected, some of the lubricant may accumulate on the head, thereby affecting the movement of the head over the disk surface.
The static charge buildup on the magnetic disk surface may be obviated by using a conductive PFPE lubricant on the magnetic disk surface. Any charge received on a disk surface containing a conductive PFPE disk lubricant may dissipate through the conductive lubricant, to a spindle motor, for example, as previously discussed. Therefore, the accumulation of lubricant in particular areas of the magnetic disk surface and on a head may be obviated.
In one embodiment of the invention, the conductive PFPE lubricant used in a FDB motor may serve as a reservoir of lubricant for a magnetic disk surface. For example, the PFPE lubricant used to formulate the conductive PFPE lubricant may be selected with an appropriate molecular weight distribution and vapor pressure to function as a reservoir. For example, the spinning of the spindle in sleeve 320 may cause some of the PFPE lubricant in the space 330 to vaporize. The vaporized PFPE lubricant may deposit on the surface of the magnetic disk surfaces and replenish the PFPE lubricant that may have been depleted due to movement of the head over the disk surface.
By dissolving hydrophobic ionic liquids in PFPE lubricants, the conductivity of PFPE lubricants may be increased. Conductive PFPE lubricants may therefore be used in components on hardware disk drive components such as FDB motors and magnetic disk surfaces to allow dissipation of unwanted charge buildup on the magnetic disks.
While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.
