Zone bonded lubrication for hard disk recording media

Details Zone bonded lubrication for hard disk recording media Zone bonded lubrication for hard disk recording media

2003-05-20

2004-10-05

Resan, Stevan A. (Department: 1773)

Stock material or miscellaneous articles

Circular sheet or circular blank

Recording medium or carrier

C428S690000, C428S690000, C428S690000, C427S131000

Reexamination Certificate

active

06800349

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to recording media disks with low bonded lubricant at the landing zone, where the head takes off and lands, for better wear resistance, and with high bonded lubricant at the data zone to protect the data from corrosion.
BACKGROUND
Most modern 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. To ensure good wear durability, the desirable lubricant retention and replenishment abilities are critical. Another issue affecting the durability and reliability of hard disk drives is the corrosion of media. Our recent study shows the disks coated with high bonded lubricants demonstrate superior corrosion resistance to those with low bonded lubricant. Hence, we need to increase the bonding of the lubricant to the disk. However, it was observed that high bonded lubricant reduces the wear durability of the media in the landing zone. To solve the dilemma, it is desired to have the disks with low bonded lubricant ratio at the landing zone, where the head takes off and lands, for better wear resistance, and with high bonded lubricant ratio at the data zone to protect the data from corrosion. In addition, during the read/write operations, the head that flies over the data zone of the disk and picks up the lubricant. This alters its flying characteristics. High bonded lubricants at the data zone would also reduce the lubricant buildup on the heads.
U.S. Pat. No. 6,096,385 (Yong) discloses a method for a making magnetic disk with uneven distribution of bonded and unbonded lubricating molecules on the surface of the disk. Yong teaches applying a pair of lubrication layers on the top and bottom surfaces of a hard disk. Then, a specially designed photo mask is provided above the lubrication layer. The photo mask has a first zone and a second zone corresponding in area to the landing zone and the data zone. The first zone of the photo mask is made to have higher ultraviolet (UV) transmittivity than the second zone. The hard disk is then UV-irradiated under the specially designed photo mask. As a result of the uneven UV transmittivity of the photo mask, a corresponding uneven distribution of bonded and unbonded lubricant molecules in the lubricating layer is produced. The disadvantages of the Yong process are the following.
First, it is limited to using lubricants that are bonded by UV. Lubricants that are substantially impervious to UV or do not bond by being exposed to UV would not be useful. Second, the lubricants for the Yong process must exhibit different degrees of bonding when exposed to different levels of UV. Third, the Yong process does not allow the use of different lubricants on different zones. Fourth, the Yong process requires the use of UV, which increases the process cost and requires safety equipment to prevent human exposure to UV.
Therefore, an improved recording medium having zone bonded lubrication with high bonded lubricant on the data zone and a low bonded lubricant on the landing zone and a process to selectively apply high bonded and low bonded lubricants to different areas of the recording media is needed.
SUMMARY OF THE INVENTION
An embodiment of this invention is a magnetic recording medium, comprising a data zone, a landing zone, a first data zone lubrication layer comprising a first data zone lubricant on the data zone and a landing zone lubrication layer comprising a landing zone lubricant on the landing zone, wherein the first data zone lubricant and the landing zone lubricant are not the same lubricant. The magnetic recording medium could further comprise a second data zone lubrication layer comprising a second data zone lubricant on the first data zone lubrication layer. The first data zone lubricant has a higher bonded ratio than that of the landing zone lubricant. The second data zone lubricant could the same as the landing zone lubricant. The combined thickness of the first data zone lubrication layer and the second data zone lubrication layer could be approximately equal to a thickness of the landing zone lubrication layer.
The first data zone lubricant has a propert

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