Stock material or miscellaneous articles – Composite – Of fluorinated addition polymer from unsaturated monomers
Reexamination Certificate
1999-08-31
2002-02-19
Resan, Stevan A. (Department: 1773)
Stock material or miscellaneous articles
Composite
Of fluorinated addition polymer from unsaturated monomers
C428S422000, C428S690000, C428S900000, C427S130000, C427S131000
Reexamination Certificate
active
06348266
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the recording, storage and reading of magnetic data, particularly rotatable magnetic recording media, such as thin film magnetic disks having textured surfaces and a lubricant topcoat for contact with cooperating magnetic transducer heads.
BACKGROUND OF THE INVENTION
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 commences when a data transducing head begins to slide against the surface of the disk as the disk begins to rotate. Upon reaching a predetermined high rotational speed, the head floats in air at a predetermined distance from the surface of the disk, where it is maintained during reading and recording operations. Upon terminating operation of the disk drive, the head again begins to slide against the surface of the disk and eventually stops in contact with and pressing against the disk. Each time the head and disk assembly is driven, the sliding surface of the head repeats the cyclic operation consisting of stopping, sliding against the surface of the disk, floating in the air, sliding against the surface of the disk, and stopping.
For optimum consistency and predictability, it is necessary to maintain each transducer head as close to its associated recording surface as possible, i.e., to minimize the flying height of the head. Accordingly, a smooth recording surface is preferred, as well as a smooth opposing surface of the associated transducer head. However, if the head surface and the recording surface are too flat, the precision match of these surfaces gives rise to excessive stiction and friction during the start up and stopping phases, thereby causing wear to the head and recording surfaces, eventually leading to what is referred to as a “head crash.” Thus, there are competing goals of reduced head/disk friction and minimum transducer flying height.
Conventional practices for addressing these apparent competing objectives involve providing a magnetic disk with a roughened recording surface to reduce the head/disk friction by techniques generally referred to as “texturing.” Conventional texturing techniques involve mechanical polishing or laser texturing the surface of a disk substrate to provide a texture thereon prior to subsequent deposition of layers, such as an underlayer, a magnetic layer, a protective overcoat, and a lubricant topcoat, wherein the texture on the surface of the substrate is intended to be substantially replicated in the subsequently deposited layers.
A typical longitudinal recording medium is depicted in FIG.
1
and comprises a non-magnetic substrate
10
, typically an aluminum (Al)-alloy, such as an aluminum-magnesium (Al—Mg)-alloy, plated with a layer of amorphous nickel-phosphorus (NiP). Alternative substrates include glass, glass-ceramic materials, and graphite. Substrate
10
typically includes, sequentially deposited on each side thereof, a chromium (Cr) or a Cr-based alloy underlayer
11
,
11
′, a cobalt (Co)-based alloy magnetic layer
12
,
12
′, a protective overcoat
13
,
13
′, typically containing carbon (C), and a lubricant topcoat
14
,
14
′. Cr underlayer
11
,
11
′ can be applied as a composite comprising a plurality of sub-underlayers
11
A,
11
A′. Cr underlayer
11
,
11
′, Co-based alloy magnetic layer
12
,
12
′ and protective overcoat
13
,
13
′, typically containing carbon, are usually deposited by sputtering techniques performed in an apparatus containing sequential deposition chambers. A conventional Al-alloy substrate is provided with a NiP plating, primarily to increase the hardness of the Al substrate, serving as a suitable surface to provide a texture, which is substantially reproduced on the disk surface.
In accordance with conventional practices, a lubricant topcoat is uniformly applied over the protective layer to prevent wear between the disk and head interface during drive operation. Excessive wear of the protective overcoat, typically comprising carbon, increases friction between the head and disk, thereby causing catastrophic drive failure. Excess lubricant at the head-disk interface causes high stiction between the head and disk. If stiction is excessive, the drive cannot start and catastrophic failure occurs. Accordingly, the lubricant thickness must be optimized for stiction and friction.
Liquid lubrication of the disk surface has at least two problems which limit its effectiveness as used in rotating storage media. First, the lubricant does not have a retention means so that when the disk rotates, the lubricant spins off the disk. The depletion of the lubricant thickness from the disk surface increases the friction between the disk and the read/write head. Second, the depletion of the thickness of the lubricant is not uniform across the surface of the disk. Where the thickness is too thin, the head can cause wear on the disk surface. 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. Other failure modes include the inability of the spindle motor to start at all due to the static friction and failure of the mechanical suspension assembly. These effects are present even though the depletion is radial in nature.
A significant factor in the performance of a lubricant topcoat is the amount of lubricant which tightly adheres to the magnetic medium, as by chemical bonding forces operating between functional groups of the lubricant molecule and the surface of the recording medium. Typical conventional lubricants, such as perfluoroalkylpolyether (PFPE) fluids such as Fomblin Z-DOL, Fomblin Tx., and Fomblin Z-Tetraol, etc., generally are comprised of molecules having 2-4 polar groups at either end of a linear molecule. The polar end-groups provide bonding of the lubricant molecules to the surface of the magnetic medium. However, polar end-functional groups are not necessarily chemically inert and consequently, such conventional lubricants may disadvantageously undergo chemical reactions prior to their application to the magnetic medium tending to decrease their bonding potential. Moreover, the conventional perfluoroalkylpolyether-based lubricants do not have an optimal molecular structure or conformation considered necessary for the increased demands of magnetic medium lubricity.
One way in which to increase bonding of the lubricant to the disk surface and therefore prevent the depletion of lubricant therefrom has been to thermally bond the lubricant to the disk surface. However, this technique disadvantageously increases the exposure of the magnetic media to corrosion and degrades the reliability of the disk. Another technique is to use a process employing exposure to high energy electron beams. The lubricant is exposed to electron beams having an energy above ten KeV. This process has been shown to produce a modified lubricant film bonded to the disk surface. However, the modified film does not contain all the required lubricating properties of the unmodified film.
Thus, a significant factor in the performance of recording media is the quality and character of the topcoat lubricant. Lubricant topcoats comprised of conventional polymeric materials as described above are typically applied as a heterogeneous mixture of different molecular weight species. The use of such mixtures, however, results in dispersal or variation of the properties thereof, depending upon the relative amounts of each molecular weight fraction present in the mixture. As a consequence, use of polymer mixtures incurs difficulties in maintaining uniform processing conditions and product quality.
It is also desirable for improved media performance to employ lubricants which form an effective functional topcoat at a thickness less than those of conventionally utilized lubricants. As indicated above, perfluoropolyether lubrican
Gubbi Vidya
Liu Youmin
Shih Chung
Resan Stevan A.
Seagate Technology LLC
LandOfFree
Amphiphillic lubricants for magnetic media does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Amphiphillic lubricants for magnetic media, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Amphiphillic lubricants for magnetic media will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2948886