Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Including a second component containing structurally defined...
Reexamination Certificate
2000-09-12
2003-07-01
Resan, Stevan A. (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Including a second component containing structurally defined...
C428S336000, C428S408000, C428S690000
Reexamination Certificate
active
06586086
ABSTRACT:
This invention relates to a magnetic recording medium having a magnetic layer of the coating type and a method for preparing the same.
BACKGROUND OF THE INVENTION
In prior art magnetic recording media of the coating type, lubrication is achieved by incorporating a lubricant such as a fatty acid or fatty acid ester in the magnetic layer or by forming an intermediate layer of such a lubricant between the non-magnetic substrate and the magnetic layer such that the lubricant may emerge on the magnetic layer surface. Such magnetic recording media have long been utilized in the form of audio tape, video tape, computer data tape and disks. Because of the advanced high-vision TV broadcasting and computer data backup technology, the demand for high capacity tape is now increasing. It is desired to increase the data density of tape. One such approach is to produce the tape in thinner film form. Specifically, the approach intends to reduce the thickness of a base film and a coating layer which constitutes the tape for thereby increasing the recording density per volume. Reducing the thickness of the coating layer, however, gives rise to the problems that the coating layer is abraded by sliding contact with the magnetic head, resulting in clogging of the magnetic head, and still performance becomes poor due to shortage of the lubricant.
Means for improving the durability of the magnetic layer include the provision of a protective layer and a lubricating layer on the magnetic layer. In JP-B 3-32139, for example, a protective layer based on a UV or electron beam-curable resin is formed on a magnetic layer by coating, and cured by irradiating UV or electron beam, and thereafter, the magnetic layer is heat treated. The protective layer is about 0.2 &mgr;m thick in Examples. This method, however, encounters the difficulty of manufacture management in the event where the protective layer is formed to a thickness of less than 0.1 &mgr;m in order to reduce the spacing loss, because precise control of the concentration of the coating solution is necessary in order to form the protective layer to a uniform thickness.
Unlike the coating type magnetic recording media, metal thin film type magnetic recording media cannot adopt formulation means such as impregnating the magnetic recording layer with a lubricant, and instead, a lubricant layer or protective layer is provided on the metal thin film. Without a lubricant layer or protective layer, there are many problems including an increased coefficient of friction, unstable tape travel, and considerably low durability. It was then proposed to form a diamond-like carbon (DLC) film as the protective layer. The DLC film ensures the manufacture of a tape which provides lower friction than the coating type magnetic recording media. The DLC film is hard enough to undergo least wear by the head. Also the DLC film is effective for reducing the deposition of dust or debris that can cause dropouts.
The provision of the DLC film does impose little difficulty to the manufacture process of metal thin film type magnetic recording media because the metal thin film is formed by vacuum deposition techniques and the DLC film uses similar techniques.
Although the DLC film has many advantages as mentioned above, it is difficult in practice to use the DLC film as the protective layer in combination with the magnetic layer of the coating type. This is because a big difference exists in manufacture process between the DLC film and the magnetic layer.
Research is now made on a computer data tape drive having an MR head built therein. What is required for the magnetic tape to be read out satisfactorily by an MR head is (1) an appropriate magnetic flux density, (2) a smooth magnetic layer surface for noise reduction, and (3) the wear resistance of the magnetic layer surface in the event where a high hardness material such as Al—Ti—C is used as the head component.
The current technology of combining the MR head with the coating type magnetic tape has substantially overcome the above problems (1) and (2), but is unsatisfactory with respect to problem (3). It is thus desired to accomplish a lubricating effect or good friction properties and improve durability (such as wear resistance) without giving rise to the above problems (1) and (2).
SUMMARY OF THE INVENTION
An object of the invention is to provide a magnetic recording medium comprising a thin magnetic layer of the coating type, having improved friction properties and durability. Another object of the invention is to provide a method for preparing the magnetic recording medium.
It has been found that a coating type magnetic recording medium can be improved in durability, friction properties and surface smoothness and optimized in magnetic flux density by forming a diamond-like carbon film on a magnetic layer.
In a first aspect, the invention provides a magnetic recording medium comprising a non-magnetic substrate, a magnetic layer on the substrate containing at least a magnetic powder and a binder and having a thickness of up to 0.15 &mgr;m, a diamond-like carbon film on the magnetic layer having a thickness of 5 to 30 nm, and a lubricating layer on the diamond-like carbon film. Preferably, the diamond-like carbon film has been formed by plasma CVD, and the magnetic layer is free of a lubricant. The magnetic recording medium is typically used in combination with an MR head.
In a second aspect, the invention provides a method for preparing a magnetic recording medium comprising the steps of forming a magnetic layer containing at least a magnetic powder and a binder on a non-magnetic substrate to a thickness of up to 0.15 &mgr;m by coating, reducing the amount of low molecular weight matter in the magnetic layer, and thereafter, forming a diamond-like carbon film on the magnetic layer to a thickness of 5 to 30 nm by plasma CVD. Most often, the low molecular weight matter contains an organic solvent, and the step of reducing the amount of low molecular weight matter in the magnetic layer includes reducing the amount of the organic solvent to 20 ppm or below.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The magnetic recording medium of the invention has a magnetic layer of the coating type on a non-magnetic substrate, a DLC film on the magnetic layer as a protective layer, and a lubricating layer thereon. It is a high density magnetic recording medium that is mainly used in the form of a magnetic tape, especially in combination with an MR head.
In order to enable high density recording and operate in combination with an MR head which is a magnetoresistance device, the magnetic layer should have a thickness of 0.15 &mgr;m or less. The provision of the DLC film as the protective film imparts to the medium lubricity and wear resistance and hence, durability enough to withstand the combined use with an MR head of high hardness material. The DLC film has smoothness enough to ensure satisfactory readout by an MR head while suppressing noise. Since the DLC film has a thickness of 5 to 30 nm, the medium has a minimized spacing loss and good reliability. On combined use with an MR head, the magnetic recording medium provides an appropriate magnetic flux density.
As a result, the magnetic recording medium of the invention has improved lubricity, a low friction coefficient, high durability, minimized spacing loss and satisfactory write/read characteristics.
The respective components of the magnetic recording medium are described below in detail as well as its manufacturing method.
DLC Film
The diamond-like carbon (DLC) film is provided as the protective film for imparting lubricity and wear resistance to the magnetic layer. The “diamond-like carbon” film used herein denotes a synthetic carbon film in which carbon atoms are bonded to high orders, specifically a hard carbon film having a refractive index of at least 1.9. For a material having a refractive index of such an order, its hardness can be approximated from its refractive index. For example, a refractive index of 1.9 corresponds to a Vickers hardness of 6,370 N/mm
2
(650 kg/mm
2
). No up
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Resan Stevan A.
TDK Corporation
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