Magnetic recording media with a multiple-layer lubricant

Details Magnetic recording media with a multiple-layer lubricant Magnetic recording media with a multiple-layer lubricant

2001-05-02

2004-01-06

Resan, Stevan A. (Department: 1773)

Stock material or miscellaneous articles

Structurally defined web or sheet

Including components having same physical characteristic in...

C428S408000, C428S421000, C428S422000, C428S690000

Reexamination Certificate

active

06673429

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to recording media having two or more layers of lubricants, the first layer comprising a lubricant mobility enhancer and the second layer comprising a lubricant.
BACKGROUND
Most modem information storage systems depend on magnetic recording due to its reliability, low cost, and high storage capacity. The primary elements of a magnetic recording system are the recording medium, and the read/write head. Magnetic discs with magnetizable media are used for data storage in almost all computer systems. Current magnetic hard disc drives operate with the read-write heads only a few nanometers above the disc surface and at rather high speeds, typically a few meters per second. Because the read-write heads can contact the disc surface during operation, a thin layer of lubricant is coated on the disc surface to reduce wear and friction.
A conventional longitudinal recording disk medium is depicted in FIG.
1
and typically comprises a non-magnetic substrate
10
having sequentially deposited on each side thereof an underlayer
11
,
11
′, such as chromium (Cr) or Cr-alloy, a magnetic layer
12
,
12
′, typically comprising a cobalt (Co)-base alloy, and a protective overcoat
13
,
13
′, typically containing carbon. Conventional practices also comprise bonding a lubricant topcoat
14
,
14
′ to the protective overcoat. Underlayer
11
,
11
′, magnetic layer
12
,
12
′, and protective overcoat
13
,
13
′, are typically deposited by sputtering techniques. The Co-base alloy magnetic layer deposited by conventional techniques normally comprises polycrystallites epitaxially grown on the polycrystal Cr or Cr-alloy underlayer. A conventional perpendicular recording disk medium is similar to the longitudinal recording medium depicted in
FIG. 1
, but does not comprise Cr-containing underlayers.
A conventional longitudinal recording disk medium is prepared by depositing multiple layers of metal films to make a composite film. In sequential order, the multiple layers typically comprise a non-magnetic substrate, one or more underlayers, a magnetic layer, and a protective carbon layer. Generally, a polycrystalline epitaxially grown cobalt-chromium (CoCr) magnetic layer is deposited on a chromium or chromium-alloy underlayer.
The seed layer, underlayer, and magnetic layer are conventionally sequentially sputter deposited on the substrate in an inert gas atmosphere, such as an atmosphere of pure argon. A conventional carbon overcoat is typically deposited in argon with nitrogen, hydrogen or ethylene. Conventional lubricant topcoats are typically about 20 Å thick.
Lubricants conventionally employed in manufacturing magnetic recording media typically comprise mixtures of long chain polymers characterized by a wide distribution of molecular weights and include perfluoropolyethers, functionalized perfluoropolyethers, perfluoropolyalkylethers (PFPE), and functionalized PFPE. PFPE do not have a flashpoint and they can be vaporized and condensed without excessive thermal degradation and without forming solid breakdown products. The most widely used class of lubricants include perfluoropolyethers such as AM 2001®, Z-DOL®, Ausimont's Zdol or Krytox lubricants from DuPont.
Lubricants are either applied to the recording media by a vapor phase lubrication process or by a dip coating technique. When lubricants are applied using a dip coating technique, the lubricant is dissolved in a solvent at low concentration, and the media are dipped into the solution and withdrawn, or the solution is pumped over the media and then drained away. As the media are lifted or the solution drained a meniscus of solution is dragged along the disc's surface, and as the solvent evaporates a thin film of the nonvolatile lubricant is left on the disc. The amount of lubricant in the film is controlled through varying either the concentration of lubricant in the solution or the rate at which the media is lifted or the solution drained, or both.
Most disk drives produced currently operate in the Contact Start/Stop (CSS) mode. Since the recording head contacts with recording media during takeoff and landing, wear due to a large number of CSS cycles is a major cause of drive failure. Furthermore, as the head-media separation continues to decrease to achieve higher recording areal density, head-disc contacts during normal operation are expected to increase. Consequently, to ensure the reliability of a disk drive, it is essential that media have good wear durability, independent of start-stop mechanisms (CSS or load-unload). To ensure good wear durability, the desirable lubricant retention and replenishment abilities are critical. When a lubricant film is removed in an area due to head-disk contacts, lubricants in the vicinity should quickly flow into lubricant-depleted area to repair the damage before next contact occurs. Insufficient lubricant mobility will lead to accumulation of damage, and an eventual premature failure. Many studies shows that a moderate surface mobility of lubricant is required to achieve good wear durability. To enhance lubricant mobility, one may either reduce the molecular weight of a lubricant or select lubricants with weakly-interacting end-groups. However, such a choice often leads to unpleasant tradeoff such as fly-stiction and enhanced lubricant evaporative loss or “spin-off.”
U.S. Pat. No. 6,099,762 (Lewis) generally discloses a dual-layer lubricant in the Background section of this patent. Lewis discloses a recording medium could have a carbon overcoat (col. 1, line 13), a lubricant, which can be a fluorocarbon or a phosphazene (col. 1, lines 17 and 18), and lubricants in separate sub-layers (col. 1, lines 25 and 26). However, there are many deficiencies in Lewis. First, the invention of Lewis is not related to a recording medium having two or more lubricant layers. Therefore, it does not disclose how one should make and use a recording medium having two or more lubricant layers. Second, Lewis treats phosphazene as a “lubricant,” but does not recognize that phosphazene could also be a lubricant mobility enhancer when phosphazene is in the form of an adsorbed layer on the substrate and a lubricant layer lies above this adsorbed layer. Third, Lewis does not disclose the order in which the “lubricants,” i.e., a fluorocarbon or phosphazene, should be deposited on a disk to form a dual-layer such that at least one constituent of a first layer would function as a mobility enhancer for the lubricant in a second layer.
A publication entitled, “MAGNETIC MATERIALS,” published on Jul. 21, 1999, of which pages
1
and
6
are relied on, states that “interactions of perfluoroaklyl ethers and phosphazene on different carbon overcoated hard disks” were studied. “Results showed that Ar sputtered carbon overcoat interacted strongly with the phosphazene molecules [in the lubricant], while the hydrogenated carbon (the current hard disk coating) did not. This interaction explains why the phosphazene molecules tended to segregate from the perfluoroalkyl ethers on the hard disk and preferentially adsorbed onto the head surface, thereby reducing the catalytic decomposition of the alumina on the perfluoroaklyl ethers.” Id. Sputtering carbon using Argon (Ar) plasma in a sputtering chamber with no hydrogen typically forms Ar sputtered carbon. On the other hand, hydrogenated carbon is typically formed if carbon sputtering is done in the presence of hydrogen.
JP 10251676 (Hirofumi) discloses a lubricant that is a mixture of perfluoropolyether and phosphazene compounds. The disadvantages of using such a mixture are the following. First, the phosphazene compound will not interact strongly with the hydrogenated carbon overcoat in accordance with the disclosure of the “MAGNETIC MATERIALS” publication. Second, even if the phosphazene compound tends to segregate on the carbon overcoat, a significant portion of the phosphazene compound will still be distributed in the bulk of the mixture, where it possibly provides no benefi

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