Solid anti-friction devices – materials therefor – lubricant or se – Lubricants or separants for moving solid surfaces and... – Heterocyclic ring compound; a heterocyclic ring is one...
Reexamination Certificate
1999-06-17
2001-11-27
Johnson, Jerry D. (Department: 1764)
Solid anti-friction devices, materials therefor, lubricant or se
Lubricants or separants for moving solid surfaces and...
Heterocyclic ring compound; a heterocyclic ring is one...
C508S308000, C540S467000, C549S351000, C549S352000, C549S353000
Reexamination Certificate
active
06323163
ABSTRACT:
TECHNICAL FIELD
This invention relates to a fluorine-containing compound especially effective for improving sliding durability of magnetic recording media, a low-scattering lubricant or surface modifier containing the compound, a lubricating film formed using the same, and a magnetic recording medium having such a lubricating film.
BACKGROUND ART
In recent years, the distance between a head and a disk has shown a tendency to become smaller because of the necessity to make magnetic disk devices have a higher recording density. The speed of revolution of a disk has also shown a tendency to increase because of the necessity to perform read/write at a high speed. This causes the head and the disk to come into contact more frequently, and moreover come into contact at a higher speed than ever. Hence, it is foreseen that disks will slide as the operating conditions become more severe than ever. Accordingly, in order to prevent magnetic layers from wearing away because of such a sliding movement, lubricants used in the outermost layers of magnetic disks have been improved in variety.
For example, a fluorine-containing compound such as a compound having piperonyl groups at both terminals of a perfluorooxyalkylene chain (Japanese Patent Application Laid-open No. 61-4727) is proposed as a lubricant which may be coated on the surfaces of magnetic disks to improve the lubricity of their surfaces to reasonably restrain the wear of magnetic layers.
However, such a lubricant may be gradually scattered by the sliding of a head. This is considered to be due to the lubricant being physically scraped off by sliding movement or due to volatilization caused by heat energy produced by sliding movement. Accordingly, low-scattering lubricants are desired since the use of a disk for a long time may cause the lubricant layer on the disk surface to become thin or, in some cases, may cause its underlying layer to become laid bare in parts.
In particular, in recent years, as the distance between the head and the disk is made smaller in order to make magnetic disk devices have a higher recording density, the head and the disk come into contact very frequently. Thus, the lubricants must be durable to cope with severe slide conditions. In particular, recently with heads and head sliders being made small-sized, the head tends to have a lower rigidity than ever. Hence, such a head has caused a problem of being broken because of its great stickiness to the disk, when the disk is started to turn.
Accordingly, a first object of the present invention is to provide a fluorine-containing compound having a good sliding performance, low scattering properties and a low stickiness, and a lubricant or surface modifier (water repellent), a lubricating film, a magnetic recording medium and a magnetic recording device which make use of such a compound.
As a lubricant having low scattering properties, Japanese Patent Applications Laid-open No. 8-36741 and No. 8-36742 disclose a proposal of a crown ether compound comprising a perfluorooxyalkyl chain and a crown ether which are linked chiefly by an imino group. Such a compound, however, tends to absorb moisture, therefore tends to cause changes in lubricating performance as a result of moisture absorption, and is not desirable for lubricating films which are used in a highly humid atmosphere over a long period of time.
Accordingly, a second object of the present invention is to provide a fluorine-containing compound having a good sliding performance, low scattering properties and a low moisture absorption, and a lubricant or surface modifier (water repellent), a lubricating film, a magnetic recording medium and a magnetic recording device which make use of such a compound.
DISCLOSURE OF THE INVENTION
In order to achieve the first object, the present inventors synthesized various fluorine-containing compounds to make studies thereon. As a result, they have discovered that the first object can be achieved by a novel fluorine-containing compound having a perfluoropolyoxyalkylene chain in the molecule and in which atomic groups containing oxyethylene moieties are bonded to both terminals of this chain (hereinafter “first compound”).
This compound of the present invention is liquid at normal temperature because it has in the molecule the perfluoropolyoxyalkylene chain, having a large molecular weight, and has a low volatility because it has the oxyethylene moieties. Hence, the use of the compound of the present invention makes it possible to maintain good lubricating performance over a longer period of time than ever.
The first compound, having oxyethylene moieties at both terminals of a perfluoropolyoxyalkylene chain, also has a lower stickiness than a compound having a perfluoropolyoxyalkylene chain to which one oxyethylene moiety is attached, and shows a small head stiction in the contact start-stop method (CSS method). Hence, its use in lubricating films is unlikely to cause a break due to sticking even when small-sized heads are used.
As a result of studies on conventional compounds having a perfluorooxyalkyl chain and a crown ether, the present inventors have also found that a high moisture absorption the compounds have is caused by the fact that they are connected by an imino linkage. The nitrogen atom in the imino linkage has so high a basicity that it reacts with NO
x
, SO
x
etc. in air to change into a nitrate, a sulfite, a sulfate and so forth. Thus, the compound in which the imino linkage is present is, as a result of its contact with atmosphere for a long time, considered to become subject to absorbing water. Incidentally, NO
x
is contained in air in large quantities in the neighborhood of roads having a lot of traffic, and SO
x
in the neighborhood of thermal power stations, where moisture absorption tends to progress.
Accordingly, in order to achieve the second object, the present invention provides a novel fluorine-containing compound having both a perfluoropolyoxyalkyl chain and an oxyethylene moiety in the molecule which are linked by a linkage other than the imino linkage, as exemplified by an amide linkage, a sulfonamide linkage, an ester linkage or an ether linkage (hereinafter “second compound”).
This second compound is also liquid at normal temperature because it has in the molecule the perfluoropolyoxyalkyl chain, having a large molecular weight, and has a low volatility because it has the oxyethylene moiety. It may also cause almost no change in lubricating performance due to moisture absorption. Hence, the use of the second compound makes it possible to maintain a good lubricating performance over a long period of time, and also this second compound has a superior storage stability.
A compound which is the first compound and in which the perfluoropolyoxyalkylene chain and the oxyethylene moieties are connected by linkages other than imino linkages is very useful because it can achieve both the first object and the second object mentioned above. Meanwhile, a compound which is the first compound and in which the perfluoropolyoxyalkylene chain and the oxyethylene moieties are connected by imino linkages is especially useful as a lubricant for cold districts because of its low pour point. Of course, it is also useful as a lubricant at places not exposed for long periods to the open air having a high humidity, because it has a good lubricating performance and has a low stickiness.
The present invention also provides a surface modifier (water repellent) that can improve water repellency of the surface to be treated, and a lubricant, both containing any of these fluorine-containing compounds of the present invention. Furthermore, the present invention provides a lubricating film containing these fluorine-containing compound of the present invention, a magnetic recording medium having the lubricating film, and a magnetic recording device including the recording medium.
REFERENCES:
patent: 4523994 (1985-06-01), Shono et al.
patent: 4554362 (1985-11-01), Shono et al.
patent: 4721795 (1988-01-01), Caporiccio et al.
patent: 4808472 (1989-02-01), Caporiccio et al.
Ishida Mina
Ito Yutaka
Matsumoto Hiroyuki
Nakakawaji Takayuki
Sasaki Hiroshi
Antonelli Terry Stout & Kraus LLP
Hitachi , Ltd.
Johnson Jerry D.
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