Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
2001-09-10
2004-02-24
Rickman, Holly (Department: 1773)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S216000, C428S336000, C428S690000, C428S690000, C428S900000
Reexamination Certificate
active
06696183
ABSTRACT:
RELATED APPLICATION DATA
The present application claims priority to Japanese Application(s) No(s). P2000-276739 filed Sep. 12, 2000, P2000-292586 filed Sep. 26, 2000 and P2000-292605 filed Sep. 26, 2000, which application(s) is/are incorporated herein by reference to the extent permitted by law.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a metallic thin film magnetic recording medium.
2. Description of the Related Art
In recent years, high-density recording has been demanded further strongly in fields of video tape recorder and the like in order to achieve high definition screen. As a magnetic recording medium corresponding to this demand, a so-called metallic thin film magnetic recording medium, in which a magnetic layer is formed by coating a nonmagnetic supporting body directly with ferromagnetic material composed of a metal or an alloy such as Co—Ni according to vacuum thin film formation technology, has been proposed. As such a magnetic recording medium, for example, a vapor-deposition tape and the like for a high-band 8-mm video tape recorder (hereinafter referred to as simply VTR) and a digital VTR have been currently produced.
The aforementioned vacuum thin film formation technology includes vacuum deposition method, sputtering method, ion plating method, vapor growth method and the like, and as the ferromagnetic metallic material, Co—Cr, Co and the like as well as the aforementioned Co—Ni have been used.
Such a magnetic recording medium of metallic magnetic thin film type is different from so-called coating type magnetic recording medium obtained by coating a nonmagnetic supporting body with coating medium produced by mixing magnetic powder with binder and the binder, which is a nonmagnetic material, is not mixed in the magnetic layer. Therefore, the charging density of the ferromagnetic metallic particle is high. Thus, the magnetic layer can be formed extremely thin, so that demagnetization by recording or loss of thickness upon reproduction is extremely small thereby indicating an excellent electromagnetic conversion in short wavelength. Further, there is such an advantage that magnetic characteristics such as coercive force, residual magnetism and rectangularity ratio can be controlled and produced stably.
Meeting a demand for further intensification of recording density in the magnetic recording medium, instead of a conventional induction type head, a magnetic resistance effect type magnetic head (MR head) has been utilized as the magnetic head for use in reproduction of recording information.
Because the MR head has a characteristic making it possible to detect minute leaking magnetic flux from the magnetic recording medium in a high sensitivity, intensifying the thinning of the magnetic layer has enabled reduction of noise, so that improvement of plane recording density can be achieved.
In the tape-like magnetic recording medium, it has been an important subject to thin the nonmagnetic supporting body containing the magnetic layer further so as to incorporate a longer magnetic tape in a cassette in order to improve the recording density per unit volume.
In the above-described metallic thin film magnetic recording medium, usually, protective layer is formed on the magnetic layer or a lining layer is formed on a main face opposite to the magnetic layer formation face in order to improve the tape durability, traveling performance and the like.
Further, in the metallic thin film magnetic recording medium, the surface has been smoothed further in order to reduce spacing loss corresponding to the trend of increased recording density.
However, if the surface of the magnetic layer is smoothed, tape's contact area with a magnetic head is increased, so that friction is increased thereby leading to increase of shearing stress generated in the magnetic layer. To protect the magnetic layer from such a strict sliding condition, it is necessary to form the protective layer on the magnetic layer.
Further, the lining layer has the function of reducing electrical resistance of the surface of the nonmagnetic supporting body, preventing traveling failure due to electric charge, improving the durability of the nonmagnetic supporting body, protecting from the generation of flaws which may be caused by friction with the head during traveling and protecting from friction between the magnetic tapes.
However, if the nonmagnetic supporting body is thinned to raise recording density per unit volume as described above, mechanical strength such as breaking resistance, breaking extension, and a product between Young's modulus of elasticity and nonmagnetic supporting body drops. Consequently, durability when an external force is applied to the magnetic tape deteriorates, and tape traveling performance and head contact performance worsen.
Further, if the thinning of the magnetic layer, which composes the magnetic recording medium, is accelerated so that the film thickness is decreased from the conventional 200 nm to 100 nm or less, the tape receives an influence such as oxidization from external environment to which the magnetic layer is exposed. As a result, its magnetic characteristic may be affected badly, so that its storage durability deteriorates relatively.
To improve mechanical strength of the nonmagnetic supporting body, instead of polyethylene terephthalate (PET), polyethylene naphthalate (PEN) conventionally used as a nonmagnetic supporting body of the magnetic tape, a high strength material such as polyamide film has been employed.
By using the polyamide film, the thickness of the nonmagnetic supporting body can be reduced to 3-5 &mgr;m.
However, the polyamide film is made of material more expensive than the conventionally marketed polyethylene terephthalate (PET) or polyethylene naphthalate (PEN) and not suitable for production and sale in large quantity as the nonmagnetic supporting body of the magnetic tape.
If the magnetic layer is formed on such a thinned nonmagnetic supporting body according to the vacuum thin film formation technology, cupping is generated in the width direction by its stress, so that traveling performance and head touch worsen.
In view of the above-described problems, the present invention intends to provide a metallic thin film magnetic recording medium of metallic magnetic thin film type adapted for the MR head, in which the magnetic layer and the nonmagnetic supporting body are thinned further, recording density per unit volume is improved, and at the same time, production cost is reduced, an influence from external environment, specifically, water vapor permeability is reduced and further cupping is reduced.
On the other hand, in a method of employing a nonmagnetic supporting body in which Young's modulus of elasticity is raised in the width direction of the magnetic tape in order to accelerate thinning of the magnetic tape, the magnetic tape is produced by high-rate extension and therefore, there is a limit in rise of Young's modulus of elasticity. Further, if the nonmagnetic supporting body is extended to raise Young's modulus of elasticity, balance in the length direction and width direction of the magnetic tape is lost, so that the configuration of the nonmagnetic supporting body worsens, thereby leading to worsening of the configuration of the magnetic tape.
According to other method for intensifying the thinning of the magnetic tape, coating medium containing plate-like filler and resin is applied onto the nonmagnetic supporting body so as to form a highly stiff layer having predetermined minute particles and then, the magnetic layer is formed on this highly stiff layer so as to improve the stiffness.
However, in this case, coupling between filler and resin acting as a vehicle is not sufficient and therefore, there is a limit in the effect of raising Young'modulus of elasticity. Further, because the highly stiff layer needs a predetermined thickness, it induces a rise in the thickness of the magnetic tape, thereby providing a problem in accelerating the thinning of the magne
Iwano Tomoe
Kanou Takashi
Motohashi Kazunari
Onodera Seiichi
Yoshida Shin-ya
Rickman Holly
Sonnenschein Nath & Rosenthal LLP
Sony Corporation
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