Coating processes – Magnetic base or coating
Reexamination Certificate
1999-12-06
2002-03-12
Beck, Shrive P. (Department: 1762)
Coating processes
Magnetic base or coating
C427S255230, C427S255500, C427S422000, C427S425000, C428S065100, C428S065800
Reexamination Certificate
active
06355300
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to disc drive assemblies comprising thin film magnetic media, and more particularly, to a method for lubricating a thin film magnetic media at the head-disc interface zone.
BACKGROUND OF THE INVENTION
Thin film magnetic media are usually prepared with a protective overcoat having a thin layer of carbon. The carbon overcoat serves to protect the underlying soft magnetic alloys against excessive frictional wear caused by the sliding action of the read-write head on the magnetic disc media. To improve the frictional properties of the head/disc interface, the carbon overcoat is typically covered with a thin topcoat of lubricant. The thin topcoat of lubricant generally has a thickness between 1 and 4 nanometers.
The lubricant topcoat may be applied using a dip coating technique. In the dip coating technique, the lubricant is dissolved in a solvent at low concentration and the magnetic disc media is dipped into the solution and withdrawn. Alternatively, the lubricant solution can be pumped over the magnetic media and then drained away. As the magnetic disc media is lifted or the lubricant solution drained, a meniscus of solution is dragged along the disc's surface. Accordingly, as the solvent evaporates, a thin film of the nonvolatile lubricant is left on the disc. The amount of lubricant in the film can be controlled either by varying the concentration of lubricant in the solution, the rate at which the media is lifted or the solution drained, or a combination of either method.
Moreover, the magnetic disc media and flying read-write head of conventional disc drives are typically extremely smooth in order to support the low fly heights required in modern disc drives. Typically, the flying read-write head lands on the surface of the disc when the drive is powered down and the disc stops spinning. However, the use of smooth magnetic disc media and read-write heads in combination with a thin layer of lubricant results in a high contact area interface and excessive static frictional forces when the drive restarts.
In some cases, the static frictional forces will exceed the capacity of the drive motor thereby resulting in a functional failure of the drive. Some disc drive mechanisms have resolved this problem by employing a dynamic load-unload mechanism. The dynamic load-unload mechanism places the flying read-write head onto the surface of the disc while it is already spinning. Similarly, the read-write head is removed from the disc before it stops spinning and, therefore, never rests on the stationary disc surface. Thus, the possibility of excessive static friction does not exist.
Despite these benefits of the dynamic load-unload mechanism, it has several shortcomings. Because the air bearing that supports the flying read-write head is not immediately established during the load process, the read-write head and the disc may experience high speed intermittent contact. This contact can damage the surface of the thin film magnetic media and result in data loss. Furthermore, the contact may also result in the head crashing into the disc surface causing a catastrophic failure of the disc drive.
Moreover, there are several drawbacks relating to the dip coating technique used to lubricate the thin film magnetic disc. For example, when applying the lubricant to the surface of the disc, the bath typically contains only a small amount of the lubricant dissolved in a solvent. This process typically results in the consumption of large quantities of solvent. Consequently, this results in increased cost and concern with environmental hazards associated with the presence of solvent vapors in the workplace.
Another drawback related to the dip lubrication method is the non-selectivity in applying the lubrication to the surface of the disc. Typically, the dip lubrication method results in the lubricant being applied to the entire surface of the disc. However, in some instances, with zone-textured media having a specific radial band designated for the load-unload region of the read-write head, the lubricant film present on the other portions of the disc surface is unnecessary and wasteful.
For example, many mechanisms load and unload the read-write head at the outside edge of the disc using some sort of ramp. The excessive lubricant on the rest of the disc's surface (e.g., the data region) may be picked up by the read-write head and alter its flying characteristics. Consequently, the presence of the lubricant film on entire disc surface is detrimental to the performance of the disc drive mechanism.
Accordingly, there exists a need for technology enabling the application of a lubricant film free of the aforementioned drawbacks of conventional dipping.
SUMMARY OF THE INVENTION
Generally, the invention relates to a method for lubricating a thin film magnetic media at the head-disc interface zone. The method comprises the steps of vaporizing the lubricant, mixing the lubricant with a carrier gas stream, and depositing a film of the lubricant at the head-disc interface zone on the surface of the magnetic media.
In one embodiment of the invention, the lubricant is vaporized using a solvent-free lubricant deposition process. Typically, the use of a solvent-free lubricant deposition process reduces the costs associated with the use of specialty solvents and their potential environmental impact. An exemplary solvent-free lubricant deposition process is discussed in currently pending patent application entitled “Method and Apparatus for Zone Lubrication of Magnetic Media” naming Michael J. Stirniman as inventor and assigned Ser. No. 09/101,793, now U.S. Pat. No. 6,099,896, the disclosure of which is herein incorporated by reference. One embodiment of this solvent-free lubrication apparatus employs a carrier gas driven vapor deposition for zone lubrication of magnetic media.
In another embodiment of the invention, the magnetic disc media has a data zone and a loading zone defined as annular cross-sections on the surface of the magnetic disc media. Furthermore, the method of lubricating the surface of the magnetic disc media involves depositing the film of the lubricant on the loading zone.
In yet another embodiment of the invention, the loading zone has an outside diameter substantially equal to the outside diameter of the magnetic disc media. Accordingly, when the lubricant in deposited onto the loading zone, the lubricant is only applied to an annular cross-section of the surface of the magnetic disc media that is located near the outer edge of the magnetic media.
In another embodiment, the invention relates to a method of applying a radial band of lubricant film to the surface of a magnetic disc media. The radial band of lubricant film is located near the outside diameter of the magnetic disc. The method comprises the steps of vaporizing the lubricant, mixing the lubricant with a carrier gas stream, and depositing a film of the lubricant on at the loading zone on the surface of the magnetic media.
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Falcone Samuel John
Stirniman Michael Joseph
Beck Shrive P.
Markham Wesley
Seagate Technology LLC
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