Stock material or miscellaneous articles – Structurally defined web or sheet – Continuous and nonuniform or irregular surface on layer or...
Reexamination Certificate
2000-11-01
2003-12-16
Resan, Stevan A. (Department: 1773)
Stock material or miscellaneous articles
Structurally defined web or sheet
Continuous and nonuniform or irregular surface on layer or...
C428S328000, C428S336000, C428S690000, C428S690000, C428S690000
Reexamination Certificate
active
06663939
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetic recording medium having a super thin film coating type magnetic layer. More particularly, it relates to a coating type magnetic recording medium adaptable to an MR (magnetic resistance) head.
2. Description of the Related Art
A magnetic recording system composed of a combination of an MR head and a coating type magnetic recording medium has come under review with a tendency toward higher density of a magnetic recording medium. For example, Japanese Patent Laid-Open Publication No.Hei 10-312525 discloses that by implementing a hexagonal ferrite powder-containing magnetic layer with a saturation magnetic flux density of from 300 to 1000 G, and a coercive force of 2000 Oe or more, or a ferromagnetic metal powder-containing magnetic layer with a saturation magnetic flux density of from 800 to 1500 G, and a coercive force of 2000 Oe or more, a magnetic recording medium excellent in cost efficiency, and ensuring a low noise and excellent in high density characteristics can be obtained. Further, Japanese Patent Laid-Open Publication No.Hei 10-302243 discloses that, by regulating the protrusion height on the magnetic layer surface and the magnetization reversal volume and by making a coercive force be 2000 Oe or more, a magnetic recording medium suitable for reproduction by an MR head and with improved durability and noise can be implemented.
On the other hand, for a method for coating a high density recording medium in recent years, Japanese Patent Publication No.Hei 05-059490 discloses a method in which a non-magnetic coating material is applied on a non-magnetic substrate, and a magnetic layer with a thickness of 1 &mgr;m or less is applied thereon while the non-magnetic coating material is still in a wet state.
However, the foregoing prior art methods are still insufficient for obtaining a low noise medium suitable for an MR head. For example, with the method in which a non-magnetic coating material is applied on a non-magnetic substrate, and a magnetic layer with a thickness of 1 &mgr;m or less is applied thereon while the non-magnetic coating material is still in a wet state as described in Japanese Patent Publication No.Hei 05-059490, the surface properties of the non-magnetic substrate directly affect the magnetic layer to cause noise degradation. Further, in actuality, a detailed description is not given to the relationship between the magnetic powder used and a noise in the prior art.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a coating type magnetic recording medium which ensures a low noise, and is suitable for a system using an MR head.
The above-described object is achieved by the following aspects of the present invention.
According to the invention, there is the provision of a magnetic recording medium for use in reproduction with an MR head, comprising: a non-magnetic substrate; a non-magnetic layer including a binder resin, in which a non-magnetic powder is dispersed, on the non-magnetic substrate; and a magnetic layer on the non-magnetic layer, wherein the magnetic layer is obtained by applying a magnetic coating material on the applied, dried and cured non-magnetic layer, the magnetic layer includes a metal magnetic powder with a mean major axis length of from 0.03 to 0.08 &mgr;m, and a saturation magnetization &sgr;
s
of from 100 to 130 Am
2
/kg, and the center line mean roughness Ra of the magnetic layer surface is 5 nm or less.
Further, according to the invention, there is the provision of a magnetic recording reproduction system for recording onto a magnetic recording medium and reproducing with a MR, the magnetic recording medium comprising: a non-magnetic substrate; a non-magnetic layer including a binder resin, in which a non-magnetic powder is dispersed, on at least one side of the non-magnetic substrate; and a magnetic layer on the non-magnetic layer, wherein the magnetic layer includes a metal magnetic powder with a mean major axis length of from 0.03 to 0.08 &mgr;m, and a saturation magnetization &sgr;
s
of from 100 to 130 Am
2
/kg, and the center line mean roughness Ra of the magnetic layer surface is 5 nm or less.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Below, the specific structure of the present invention will be described in details.
In general, when an MR head is used as a reproducing head, the reproducing output obtainable is several times higher than a conventional magnetic head. On the other hand, a higher noise is also detected as compared with the magnetic head. Therefore, when the MR head is used, how to control the noise at a low level is a key factor.
In the present invention, as the magnetic powder, an acicular or a spindle-shaped metal magnetic powder is used. The metal magnetic powder is required to have a mean major axis length of from 0.03 to 0.08 &mgr;m, and more preferably from 0.04 to 0.07 &mgr;m for reducing a noise. If the mean major axis length is smaller than 0.03 &mgr;m, the metal magnetic powder is insufficiently dispersed. Consequently, the insufficient dispersion results in a large noise. On the other hand, if it exceeds 0.8 &mgr;m, a magnetic noise is increased due to the large size of the magnetic powder.
Further, the saturation magnetization &sgr;
s
of the metal magnetic powder used is from 100 to 130 Am
2
/kg, and more preferably from 110 to 125 Am
2
/kg. If it is smaller than 100, the output power becomes insufficient. In contrast, if it is larger than 130, the output power is sufficient. However, the magnetic noise is also accordingly increased, resulting in a disadvantageous condition for reproduction with an MR head. Further, magnetic flocculation in the magnetic coating material increases with an increase in &sgr;
s
As a result, there occur problems that the coating properties are aggravated, and the magnetic powder becomes difficult to be oriented. Further, by setting the X-ray crystal particle size Dx of the metal magnetic powder at from 50 to 150 Å, and preferably at 50 to 120 Å, the magnetic noise can be effectively reduced. Still further, by setting &sgr;
s
(Am
2
/kg)/Dx(Å) at 0.9 or less, preferably at 0.8 or less, and more preferably at 0.7 or less, the balance between the magnetic noise and the output power can be optimized with ease.
Such a metal magnetic powder preferably contains a magnetic metallic element such as &agr;-Fe, Fe—Co, Fe—Co—Ni, Co, or Co—Ni as a main component, and contains preferably 70 wt % or more, and preferably 75 wt % or more of a metal (Fe, Co, Ni, or the like), or an alloy in the magnetic powder.
For reducing a noise, it is important for the metal magnetic powder to have no branching, and extremely less lattice defects and pores on the magnetic powder surface, and has a uniform particle size.
Such a magnetic powder can be obtained in the following manner.
With a first method, to an aqueous solution of a ferrous salt such as iron chloride or iron sulfate, added is an alkali such as cobalt chloride or sodium hydroxide for neutralization. The solution is heated while blowing an oxidizing gas therein to effect the oxidization reaction, resulting in the formation of an acicular goethite (&agr;-FeOOH). The resulting goethite is heat-treated in a non-reducing atmosphere to be dehydrated, resulting in the formation of &agr;-Fe
2
O
3
. Subsequently, the resulting &agr;-Fe
2
O
3
is reduced while blowing a hydrogen gas therein to obtain a metal magnetic powder. In this manufacturing method, by setting the amount of alkali to be two or more times, and preferably from 3 to 10 times the neutralization equivalent, the resulting goethite has less branching. Further, addition of Al or Si therein during the goethite-yielding reaction can prevent the goethite from sintering due to heat and thus control the shape, and hence it is preferable. The addition of Si is also effective for improving the coercive force. Whereas, when the heat-treatment temperature in the dehydration process of the goethite is set to be from 400 to 700° C., the resulting &agr;-
Resan Stevan A.
TDK Corporation
LandOfFree
Magnetic recording medium does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Magnetic recording medium, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Magnetic recording medium will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3131605