Stock material or miscellaneous articles – Structurally defined web or sheet – Including components having same physical characteristic in...
Reexamination Certificate
2000-02-16
2001-07-31
Resan, Stevan A. (Department: 1773)
Stock material or miscellaneous articles
Structurally defined web or sheet
Including components having same physical characteristic in...
C428S216000, C428S323000, C428S336000, C428S690000, C428S900000
Reexamination Certificate
active
06268043
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetic recording medium, and more particularly to a magnetic recording medium (and more particularly to a coating-type magnetic recording medium incorporating a magnetic coating film as a magnetic layer thereof), such as a magnetic tape or a magnetic disc, having a magnetic layer (in particular, a magnetic layer of a type containing magnetic powder and a binder as main components thereof) formed on a non-magnetic support member thereof.
2. Description of the Related Art
In recent years, magnetic recording mediums have been widely employed as recording mediums or storage mediums for audio apparatuses, video apparatuses, computers and the like. The need for the magnetic recording mediums has considerably been raised.
In general, a magnetic recording medium of the foregoing type has a structure that a magnetic layer composed of magnetic powder and a binder is formed on a non-magnetic support member made of polyester film and the like. In general, the magnetic layer is formed by applying or transferring, to the non-magnetic support member, a magnetic coating material, in which magnetic powder is dispersed in a composition containing a binder.
The magnetic layer is formed by, for example, coating a non-magnetic support member made of polyester or polyethylene terephthalate (PET) with a magnetic coating material prepared by dispersing powder of a magnetic alloy or the like, the main component of which is magnetic oxide, such as ferrite or chrome oxide, or Fe, Co or Ni in a binder made of organic polymer material.
The magnetic recording medium manufactured as described above is called a so-called coating type magnetic recording medium, which is required to improve the electromagnetic conversion characteristic thereof.
To realize excellent electromagnetic conversion characteristics of the magnetic recording medium of the foregoing type, enlargement of the output, elimination of noise and improvement of the surface characteristics are required. If the surface characteristics are improved, there arises a problem in that bias noise is intensified.
To prevent bias noise, it might be feasible to employ magnetic powder having a large specific surface area (SSA). In the foregoing case, the size of each of particles is reduced. Thus, the magnetic energy is reduced excessively to maintain a sufficiently high residual magnetic flux density. Therefore, there arises a problem in that reproduction output is reduced.
To prevent reduction in the reproduction output caused from an excessive spacing loss in a short wavelength region, minimization of asperities of the magnetic layer is required. If the surface characteristics are improved excessively, a defects in the movement, such as the foregoing bias noise, TN (Tape Noise) and stick, occur during movement of the tape. Therefore, an optimum coating film is required.
To meet the foregoing requirement, a contrivance has been suggested with which a magnetic layer having a multi-layered structure is employed.
A magnetic recording medium having a structure in which a first magnetic layer and a second magnetic layer are stacked on a non-magnetic support member will now be considered. Changes of the specific surface area of magnetic powder for use in the first magnetic layer and the second magnetic layer, the coercive force of each magnetic layer, the residual magnetic flux density and the film thickness permits satisfactory electromagnetic conversion characteristics to be obtained.
Although the electromagnetic conversion characteristics of the foregoing magnetic recording medium can somewhat be improved, both of satisfactory durability and excellent reliability cannot easily be realized while improved electromagnetic conversion characteristics are being maintained because of limitation of the manufacturing process. To realize satisfactory characteristics, magnetic powder and each magnetic layer must meet furthermore severe requirements.
SUMMARY OF THE INVENTION
In view of the foregoing, an object of the present invention is to provide a magnetic recording medium which is capable of simultaneously realizing satisfactory durability and excellent reliability while improved electromagnetic conversion characteristics are being maintained.
To achieve the above-mentioned object, according to one aspect of the present invention, there is provided a magnetic recording medium comprising: a non-magnetic support member; and a magnetic layer formed on the non-magnetic support member and mainly composed of magnetic powder and a binder and having a two-layer structure composed of a first magnetic layer and a second magnetic layer, wherein Young's modulus of the first magnetic layer is 140×10
5
N/m
2
to 160×10
5
N/m
2
and Young's modulus of the second magnetic layer is 45×10
5
N/m
2
to 50×10
5
N/m
2
.
Since the Young's modulus of the first magnetic layer satisfies the above-mentioned range, a satisfactory durability can be improved and required contact with a magnetic head can be maintained. Moreover, reduction in the bonding strength can be prevented.
Since the Young's modulus of the secured magnetic layer satisfies the above-mentioned range, a problem of separation of the coating film can be prevented. Moreover, a problem of sticking can be prevented.
Other objects, features and advantages of the invention will be evident from the following detailed description of the preferred embodiments described in conjunction with the attached drawings.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
An embodiment of a magnetic recording medium according to the present invention will now be described.
The magnetic recording medium according to the present invention is a so-called coating-type magnetic recording medium having a magnetic layer formed by applying a magnetic coating material.
A main characteristic of the magnetic layer lies in that it has a two-layer structure composed of a first magnetic layer and a secured magnetic layer each of which has an appropriate Young's modulus.
Specifically, the Young's modulus of the first magnetic layer is 140×10
5
N/m
2
to 160×10
5
N/m
2
and the Young's modulus of the second magnetic layer is 45×10
5
N/m
2
to 50×10
5
N/m
2
.
As the Young's modulus of the first magnetic layer is enlarged, the durability can furthermore be improved. If the Young's modulus is higher than 160×10
5
N/m
2
, satisfactory contact with the magnetic head cannot be maintained. In the foregoing case, the difference in the output level between the right and left channels (Rch and Lch) is enlarged excessively and/or reduction in the bonding strength occurs. If the Young's modulus is lower than 140×10
5
N/m
2
, sticking easily occurs. Therefore, satisfactory movement characteristics cannot be realized.
If the Young's modulus of the second magnetic layer is higher than 50×10
5
N/m
2
, the bonding strength, which is a physical characteristic, is reduced. Thus, separation of the coating film sometimes occurs. If the Young's modulus of the second magnetic layer is lower than 45×10
5
N/m
2
, sticking easily occurs similar to the structure in which the Young's modulus of the first magnetic layer is low.
Ferromagnetic powder can be used as magnetic powder for constituting the magnetic layer of the magnetic recording medium according to the present invention. The ferromagnetic powder is exemplified by: ferromagnetic metal powder, such as metal, such as Fe, Co or Ni or an alloy containing the foregoing metal; plate-like hexagonal ferrite, such as barium ferrite; &ggr;-iron oxide; &ggr;-iron oxide containing cobalt: magnetite; magnetite containing cobalt; and CrO
2
.
To obtain satisfactory output characteristics and bias noise, it is preferable that the specific surface area (a BET value) of magnetic powder for use in the first magnetic layer is 42 m
2
/g to 46 m
2
/g and that of the magnetic powder for use in the second magnetic layer is 32 m
Adachi Norio
Koizumi Takeshi
Sato Miwako
Resan Stevan A.
Sonnnenschein, Nath & Rosenthal
Sony Corporation
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