Coating processes – Magnetic base or coating – Magnetic coating
Reexamination Certificate
2001-04-24
2002-06-11
Pianalto, Bernard (Department: 1762)
Coating processes
Magnetic base or coating
Magnetic coating
C427S128000, C508S149000
Reexamination Certificate
active
06403149
ABSTRACT:
FIELD OF INVENTION
The invention relates to a lubricant composition and methods for coating a substrate such as magnetic media with a lubricant.
BACKGROUND OF THE INVENTION
Magnetic media is commonly used in the computer industry for storing large amounts of data. Magnetic recording occurs by moving magnetic media past a magnetic record head consisting of a small electromagnet with a gap. To record information on the magnetic media, a current is applied to the windings of the electromagnet creating a magnetic field in the gap region. The magnetic field affects the polarity of the magnetic materials in the magnetic media that are in close proximity to the head gap. Changing the direction of current flow can reverse the direction of magnetization and the polarity of the magnetic materials. To read information from magnetic media, a read head constructed similarly to the record head is brought into close proximity with the magnetic media. The magnetic field of the magnetic media induces a voltage in the read head. The voltage changes when the direction of the magnetic field from the magnetic media changes.
During normal operation, the magnetic media is moved or rotated relative to the record head with a small space between the media and the head. At the end of the recording process, the magnetic media is often in direct physical contact with the head. The frictional force produced can wear both the head and the magnetic media. Eventually, the frictional force can become large enough to damage either the media or the head.
To minimize the wear of the magnetic disk and head, a lubricant is placed on the surface of the magnetic media. The presence of the lubricant improves the durability of the magnetic media. Typically, the lubricant is a perfluoropolyether (PFPE) with functionalized end groups. Perfluoropolyether lubricants are chemically inert, thermally stable, moisture repellent compositions that possess relatively low surface tension, good lubricity and low volatility. As a result, they can be effective and long-lasting lubricants for magnetic media.
The trend in the computer industry is to increase the recording density. Increasing recording density can be achieved by increasing the output signal of the magnetic media. However, a lubricant layer between the record head and the magnetic material of the magnetic media diminishes the intensity of the signal that can be recorded or read. The decreased signal intensity is due, at least in part, to an increased distance between the head and the magnetic material due to the presence of the lubricant layer. Consequently, to maximize the output signal, a thin lubricant coating is often preferred. State-of-the-art magnetic media typically has a lubricant layer thickness below about 2 nm. The lubricant usually is applied as a dilute solution in a suitable solvent. After application of the lubricant composition, the solvent is evaporated leaving a thin, uniform lubricant coating.
Perfluoropolyethers have been extensively used as lubricants for magnetic media. Various perfluoropolyether lubricants have been described, for example, in U.S. Pat. No. 4,721,795 (Caporiccio et al.) and U.S. Pat. No. 5,049,410 (Johary et al.) Many perfluoropolyether lubricants contain a mixture of perfluoropolyether compounds with a variety of molecular weights and structures. These lubricants have limited solubility in most solvents.
A particularly effective solvent for perfluoropolyethers is 1,1,2-trichloro-1,2,2-trifluoroethane. This chlorofluorocarbon solvent offers the additional advantage of being relatively volatile so it can be removed readily after application of the lubricant composition to magnetic media. However, the 1987 Montreal Protocol calls for reductions in the use of chlorofluorocarbons to minimize degradation of the stratospheric ozone layer.
Certain perfluorinated alkanes have been used in place of chlorofluorocarbons as perfluoropolyether solvents such as those described in U.S. Pat. No. 4,721,795 (Caporiccio et al.). Additionally, U.S. Pat. No. 5,049,410 (Flynn et al.) discloses the use of a perfluorinated, nonaromatic cyclic organic solvent for dissolution of polyfluoropolyether lubricants. However, some of these compounds tend to have relatively long atmospheric lifetimes and can potentially contribute to global warming.
Thus, there is a need for solvents with short atmospheric lifetimes that dissolve polyfluoropolyether lubricants. The invention provides fluorinated ketone solvents with these desirable characteristics.
SUMMARY OF THE INVENTION
The invention provides a lubricant composition comprising about 10 to about 10,000 ppm perfluoropolyether lubricant and about 90 to about 99.9 weight percent fluorinated ketone solvent based on the weight of the lubricant composition. The lubricant compositions can further comprise about 0.1 to about 1000 ppm of an additive such as a cyclic phosphazene compound. The lubricant composition typically has low solubility for possible contaminants such as water, silicones, and general hydrocarbons. Additionally, the lubricant composition can have low global warming potential.
The fluorinated ketone solvent of the invention typically has a total of 5 to 10 carbon atoms. In some embodiments, the fluorinated ketone has 6 to 8 carbon atoms. The solvent can be a perfluoroketone, a compound in which all of the hydrogen atoms on the carbon backbone are replaced with fluorine. Alternatively, the fluorinated ketone solvent can have up to two hydrogen atoms and up to two non-fluorine halogen atoms including bromine, chlorine, and iodine attached to the carbon backbone. One or more heteroatoms can interrupt the carbon backbone of the molecule.
More than one fluorinated ketone solvent can be used in the lubricant composition. In some embodiments, one or more miscible solvents can replace a portion of the fluorinated ketone solvent. For example, up to about 10 weight percent of the fluorinated ketone can be replaced with another miscible solvent.
Typically, the perfluoropolyether lubricant comprises a perfluoropolyether molecule represented by the formula:
A&Brketopenst;(C
y
F
2y
)O(C
4
F
8
O)
k
(C
3
F
6
O)
m
(C
2
F
4
O)
n
(CF
2
O)
p
(C
z
F
2z
)&Brketclosest;A′ I
where y and z are integers independently ranging from 0 to about 20. The variables k, m, n, and p are integers independently ranging from 0 to about 200; the sum of k, m, n, and p ranges from 2 to about 200. Groups A and A′ are independently selected monovalent organic moieties.
Another aspect of the invention provides a method of lubricating a substrate. The method comprises applying a coating of a lubricant composition to a substrate followed by drying the coating to form a lubricant film on the surface of the substrate. Typically, the substrate is magnetic media such as a thin film or hard disk.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS OF THE INVENTION
The invention relates to a lubricant composition and methods of coating a substrate with a lubricant. In particular, the invention provides a lubricant composition comprising about 10 to about 10,000 ppm of a perfluoropolyether lubricant and about 90 to about 99.9 weight percent fluorinated ketone solvent based on the weight of the lubricant composition. The lubricant composition can be applied to form a thin, uniform layer of lubricant on a substrate. The substrate is typically magnetic media such as a thin film or hard disk.
The fluorinated ketone solvent of the invention typically has a total of 5 to 10 carbon atoms. In some embodiments, the fluorinated ketone has 6 to 8 carbon atoms. The fluorinated ketone solvent typically has a boiling point less than about 150° C. In some embodiments, the boiling point is less than about 100° C. To provide adequate solvency for the perfluoropolyether lubricant, the fluorinated ketone solvent is highly fluorinated. The solvent can be a perfluoroketone, a compound in which all of the hydrogen atoms on the carbon backbone are replaced with fluorine. Alternatively, the fluorinated ketone solvent can have up to two hydrogen atoms and up t
Kehren Jason M.
Minday Richard M.
Parent Michael J.
3M Innovative Properties Company
Jordan Robert H
Pianalto Bernard
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