Stock material or miscellaneous articles – Circular sheet or circular blank – Recording medium or carrier
Reexamination Certificate
2002-03-27
2004-06-22
Resan, Stevan A. (Department: 1773)
Stock material or miscellaneous articles
Circular sheet or circular blank
Recording medium or carrier
C428S421000, C428S704000, C428S690000, C428S690000, C428S336000
Reexamination Certificate
active
06753060
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
This application discloses subject matter related to subject matter disclosed in co-pending, commonly assigned U.S. patent application Ser. No. 09/986,910 filed Nov. 13, 2001.
FIELD OF THE INVENTION
The present invention relates to an improved method for increasing or enhancing the performance, e.g., durability, of a thin film or layer of a composite lubricant material applied to the surface of a thin film recording medium, particularly when the latter is utilized in combination with a flying head read/write transducer in Contact Start/Stop (“CSS”) operation, and to improved thin film recording media obtained thereby. The invention finds particular utility in the manufacture and use of thin film type magnetic or magneto-optical (“MO”) data/information storage and retrieval media comprising a layer stack or laminate of a plurality of thin film layers formed on a suitable substrate, e.g., a disk-shaped substrate, wherein a thin topcoat layer comprised of a composite lubricant material is applied to a carbon-based protective overcoat layer forming the upper surface of the layer stack or laminate for improving tribological performance of the media when utilized with read/write transducer heads operating at very low flying heights.
BACKGROUND OF THE INVENTION
Magnetic and MO media are widely employed in various applications, particularly in the computer industry for data/information storage and retrieval purposes. A magnetic medium in, e.g., disc form, such as utilized in computer-related applications, comprises a non-magnetic, disk-shaped substrate, e.g., of glass, ceramic, glass-ceramic composite, polymer, metal, or metal alloy, typically an aluminum (Al)-based alloy such as aluminum-magnesium (Al-Mg), having at least one major surface on which a layer stack or laminate comprising a plurality of thin film layers constituting the medium are sequentially deposited. Such layers may include, in sequence from the substrate deposition surface, a plating layer, e.g., of amorphous nickel-phosphorus (Ni-P), a polycrystalline underlayer, typically of chromium (Cr) or a Cr-based alloy such as chromium-vanadium (Cr-V), a magnetic layer, e.g., of a cobalt (Co)-based alloy, and a protective overcoat layer, typically of a carbon (C)-based material, e.g., diamond-like carbon (“DLC”) having good tribological properties. A similar situation exists with MO media, wherein a layer stack or laminate is formed on a substrate deposition surface, which layer stack or laminate typically comprises a reflective layer, e.g., of a metal or metal alloy, one or more rare-earth thermo-magnetic (RE-TM) alloy layers, one or more transparent dielectric layers, and a protective overcoat layer, e.g., a DLC layer, for functioning as reflective, transparent, writing, writing assist, and read-out layers, etc.
Thin film magnetic and MO media in disk form, such as described supra, are typically lubricated with a thin topcoat film or layer comprised of a polymeric lubricant, e.g., a perfluoropolyether, to reduce wear of the disc when utilized with data/information recording and read-out transducer heads operating at low flying heights, as in a hard disk system functioning in a contact Start/Stop (“CSS”) mode. Conventionally, the thin film of lubricant is applied to the disc surface(s) during manufacture by dipping into a bath containing a small amount of lubricant, e.g., less than about 1% by weight of a fluorine-containing polymer, dissolved in a suitable solvent, typically a perfluorocarbon, fluorohydrocarbon, or hydrofluoroether.
Thin film magnetic recording media are conventionally employed in disk form for use with disk drives for storing large amounts of data in magnetizable form. Typically, one or more disks are rotated on a central axis in combination with data transducer heads. In operation, a typical contact start/stop (“CSS”) cycle commences when the 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 due to dynamic pressure effects caused by the air flow generated between the sliding surface of the head and the disk. During reading and recording 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 head can be freely moved in both the circumferential and radial directions, allowing data to be recorded on and retrieved from the disk at a desired position. Upon terminating operation of the disk drive, the rotational speed of the disk decreases and the head again begins to slide against the surface of the disk and eventually stops in contact with and pressing against the disk. Thus, the transducer head contacts the recording surface whenever the disk is stationary, accelerated from the static position, and during deceleration just prior to completely stopping. Each time the head and disk assembly is driven, the sliding surface of the head repeats the cyclic sequence consisting of stopping, sliding against the surface of the disk, floating in air, sliding against the surface of the disk, and stopping.
It is considered desirable during reading and recording operations, and for obtainment of high areal recording densities, to maintain the transducer head(s) as close to the associated recording surface(s) as is possible, i.e., to minimize the “flying height” of the head(s). Thus a smooth recording surface is preferred, as well as a smooth opposing surface of the associated transducer head, thereby permitting the head and the disk surface to be positioned in close proximity, with an attendant increase in predictability and consistent behavior of the air bearing supporting the head during motion.
The lubricity properties of disk-shaped recording media are generally measured and characterized in terms of dynamic and/or static coefficients of friction. The former type, i.e., dynamic friction coefficient, is typically measured utilizing a standard drag test in which the drag produced by contact of a read/write transducer head with a disk surface is determined at a constant spin rate, e.g., 1 rpm. The latter type, i.e., static coefficients of friction (also known as “stiction” values), are typically measured utilizing a standard contact start/stop (“CSS”) test in which the peak level of friction is measured as the disk starts rotating from zero (0) rpm to a selected revolution rate, e.g., 5,000 rpm. After the peak friction has been measured, the disk is brought to rest, and the start/stop process is repeated for a selected number of start/stop cycles. An important property of a disk which is required for good long-term disk and drive performance is that the disk retain a relatively low coefficient of friction after many start/stop cycles or contacts with the read/write transducer head, e.g., 20,000 start/stop cycles.
The most commonly employed lubricants utilized with thin film, disk-shaped magnetic and MO media, i.e., perfluoropolyether (“PFPE”)-based lubricants, perform well under ambient conditions but not under conditions of higher temperature and high or low humidity. Studies, as described in, for example U.S. Pat. No. 5,587,217, the entire disclosure of which is incorporated herein by reference, have indicated that the tribological properties, and perhaps corrosion resistance, of perfluoropolyether-based lubricants utilized in the manufacture of thin film recording media can be substantially improved by addition thereto of an appropriate amount of a cyclotriphosphazene-based lubricant additive, e.g., a polyphenoxy cyclotriphosphazene comprising substituted or unsubstituted phenoxy groups, to form what is termed a “composite lubricant”.
Currently, bis(4-fluorophenoxy)—tetrakis (3-trifluoromethyl phenoxy) cyclotriphospazene (available as X-1P™ from Dow Chemical Co., Midland, Mich.) is the additive most commonly utilized with perfluoropolyether-based lubricants for forming composite lubricants for use with thin f
Gui Jing
Liu Jianwei
Liu Wen Hong
Stirniman Michael Joseph
McDermott & Will & Emery
Resan Stevan A.
Seagate Technology LLC
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