Stock material or miscellaneous articles – Composite – Of fluorinated addition polymer from unsaturated monomers
Reexamination Certificate
2003-11-18
2004-11-23
Resan, Stevan A. (Department: 1773)
Stock material or miscellaneous articles
Composite
Of fluorinated addition polymer from unsaturated monomers
C428S690000, C428S690000, C428S690000, C428S690000
Reexamination Certificate
active
06821627
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to magnetic recording media containing embedded servo-marks in the media and a lubricant topcoat and to a method for manufacturing such magnetic recording media. The present invention has particular applicability in forming lubricant topcoats for use in high areal recording density magnetic recording media with increased data reading speed.
BACKGROUND ART
Thin film magnetic recording disks and disk drives are conventionally employed for storing large amounts of data in magnetizable form. In operation, a typical contact start/stop (CSS) method involves a floating transducer head gliding at a predetermined distance from the surface of the disk due to dynamic pressure effects caused by air flow generated between the sliding surfaces of the transducer head and the disk. During reading and recording (writing) operations, the transducer head is maintained at a controlled distance from the recording surface, supported on a bearing of air as the disk rotates, such that the transducer head can be freely moved in both the circumferential and radially directions allowing data to be recorded on and retrieved from the surface of the disk at a desired position in a data zone.
In conventional hard disc drives, data are stored in terms of bits along tracks. In operation, the disc is rotated at relatively high speed, and the magnetic head assembly is mounted on the end of a support or actuator arm, which positions the head radially on the disc surface. If the actuator arm is held stationary, the magnetic head assembly will pass over a circular path on the disc, i.e. over a track, and information can be read from or written to that track. Each concentric track has a unique radius, and reading and writing information from or to a specific track requires the magnetic head to be located above the track. By moving the actuator arm, the magnetic head assembly is moved radially on the disc surface between tracks. Many actuator arms are rotary, wherein the magnetic head assembly is moved between tracks by activating a servomotor which pivots the actuator arm. A linear actuator may alternatively be used to move a magnetic head assembly inward or outward on the disc along a straight line.
To record information on the disc, the transducer creates a highly concentrated magnetic field in close proximity to the magnetic recording medium. During writing, the strength of the concentrated magnetic field directly under the write transducer is greater than the coercivity of the recording medium (known as “saturating” the medium), and grains of the recording medium at that location are magnetized with a direction which matches the direction of the applied magnetic field. The grains of the recording medium retain their magnetization after the saturating magnetic field is removed. As the disc rotates, the direction of the writing magnetic field is alternated based on bits of the information being stored, thereby recording a magnetic pattern on the track directly under the write transducer.
On each track, typically eight bits form a byte and bytes of data are grouped as sectors. Reading or writing a sector requires knowing the physical location of the data in the data zone so that the servo-controller of the disk drive can accurately position the read/write heads in the correct location at the correct time. Most disc drives use embedded “servo patterns” of recorded information on the disc. The servo patterns are read by the magnetic head assembly to inform the disc drive of track location. In conventional disc drives, tracks typically include both data sectors and servo patterns and each servo pattern typically includes radial indexing information, as well as a “servo burst”. A servo burst is a centering pattern to precisely position the head over the center of the track. Because of the locational precision needed, writing of servo patterns requires expensive servo-pattern writing equipment and is somewhat of a time consuming process.
A conventional approach to the servo-sensing problem includes the use of phisical voids or depressions in the magnetic layer between tracks formed by stamping or otherwise physically marking a pattern on the disc to function as servo information. A magnetic material layer is then applied at a consistent thickness over the entire disc surface. When this type of disc is used, the distance from the magnetic head to magnetic material in the depressions is further than the distance from the magnetic head to magnetic material in the track. The increased distance both reduces the strength of the signal recorded in the depressions and reduces the contribution from the depressions to the magnetic field sensed by the read head.
While the depressions or voids formed in the disc are helpful in increasing track density, they tend to reduce the tribological performance of the disc assembly. For example, during operation of the magnetic recording medium, the slider no longer travels over a smooth surface, causing several mechanical performance drawbacks. The drawbacks include modulation of fly height when encountering servo patterns, fly height perturbations due to topography changes from the track width definition, glide defects from the stamping process, and disc distortion due to the servo patterning process. It is thus preferred to provide the servo pattern without surface topography.
The application of the protective layer and the topical lubricant assist in providing high durability and reliability of thin film recording media. In accordance with conventional practices, a lubricant topcoat is applied over the protective layer to prevent wear between the disk and head interface during drive operation.
Fluoropolyether lubricants are of particular interest in lubricating magnetic recording media. These lubricants are uniquely suited to form lubricant topcoats on magnetic media because of such properties as chemical inertness, low vapor pressure, low surface tension, high thermal stability, stability under high shear stress and good boundary lubrication properties. Among the many lubricants available, liquid perfluoropolyethers (PFPE) are the most typically used in forming topcoat lubricants on magnetic recording media.
Liquid lubrication of the disk surface encounters several problems, however, which limit its effectiveness as used in rotating storage media. For example, it is well known that non-bonded lubricants will spin off a thin film disk with a carbon overcoat. Typically, PFPE lubricants do not have a retention means so that when the disk rotates, the lubricant tends to spins off the disk. The depletion of the lubricant from the disk surface increases the friction between the disk and the read/write head.
Further, the depletion of the lubricant results in non-uniformity across the surface of the disk resulting in additional operational difficulties. For example, where the thickness is too thin, the head can cause wear on the disk surface and where the lubricant thickness is too great, the head will become stuck in the lubricant (from static friction) and the head or disk could be damaged when the head suddenly becomes unstuck due to the rotating disk.
Dominguez-Burguette et al. in U.S. Pat. No. 4,404,247 disclose anchoring a polymerizable composition directly to a metallized substrate by a complex system which includes an inner polymeric film and an outer polymeric film. The inner polymer is made from a film forming aromatic or heterocyclic polymerizable monomer and a vinyl aromatic polymer and the outer polymer contains a compound having a perfluoropolyether segment. Dominguez-Burguette et al. disclose that such a system would adequately protect a metallic thin film and teach away from the use of a hard protective coating on magnetic thin film media. Several other patents to Dominguez-Burguette et al., such as U.S. Pat. Nos. 4,526,833; 4,569,962; 4,671,999; and 4,705,699, disclose additional ingredients in creating the complex two phase polymer coating system.
Literature exists on bonding lubricants on to the surface of recording media
Rauch Gary
Stirniman Michael
Wang Li-Ping
McDermott Will & Emery LLP
Resan Stevan A.
Seagate Technology LLC
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