Stock material or miscellaneous articles – Circular sheet or circular blank – Recording medium or carrier
Reexamination Certificate
2002-07-15
2004-03-30
Resan, Stevan A. (Department: 1773)
Stock material or miscellaneous articles
Circular sheet or circular blank
Recording medium or carrier
C428S304400, C428S315700, C428S329000, C428S336000, C428S690000
Reexamination Certificate
active
06713149
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a coating type magnetic recording medium (i.e., a magnetic recording particulate medium) capable of high density recording, in particular, a magnetic recording medium for high density recording comprising a magnetic layer containing a hexagonal ferrite powder.
BACKGROUND OF THE INVENTION
In the field of the magnetic disc, along with the increase in the amount of data to be dealt with, the increase of the capacity of a floppy disc has been demanded.
In the field of the magnetic tape also, with the prevalence of the office computer, such as minicomputers, personal computers and work stations, magnetic tapes for recording computer data as external storage media (a so-called backup tape) have been eagerly studied. For putting magnetic tapes for such usage to practical use, the improvement of recording capacity has been strongly demanded conjointly with the miniaturization of a computer and the increase of information processing ability (i.e., the increase of throughput) for achieving high capacity recording and the miniaturization.
A magnetic recording medium comprising a magnetic layer containing barium ferrite (BaFe) has been used. For example, the invention which restricts a squareness ratio SQ in the perpendicular direction to the range of from 0.3 to 0.55, and a magnetic layer thickness to 0.8 &mgr;m or less is disclosed in JP-A-8-235570 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”), and the invention which restricts a squareness ratio SQ in the perpendicular direction to the range of from 0.3 to 0.53, and the particle size of magnetic substances to 20 to 200 nm is disclosed in JP-B-7-040343 (the term “JP-B” as used herein means an “examined Japanese patent publication”).
Since magnetic heads working with electromagnetic induction as the principle of operation (induction type magnetic heads) are usually used in these magnetic recording media, their use in the field of higher density recording and reproduction is limited. That is, it is necessary to increase the number of winding of the coil of a reproduction head to obtain larger reproduction output, but when the winding number increases, the inductance increases and the resistance at high frequency heightens, as a result, the reproduction output lowers. Reproduction heads which work with MR (magneto-resistance) as the principle of operation are proposed and come to be used in hard discs in recent years. As compared with the induction type magnetic disc, several times of reproduction output can be obtained by the MR head. Further, since an induction coil is not used in the MR head, noises generated from instruments, e.g., impedance noises, are extremely reduced, therefore, it becomes possible to obtain a great S/N ratio by lowering the noise coming from magnetic recording media. In other words, good recording and reproduction can be done and high density recording characteristics can be drastically improved by lessening the noise of magnetic recording media hiding behind the noises coming from instruments.
SQ, a magnetic layer thickness and the particle size of magnetic substances are restricted in conventional magnetic recording media as described above, but characteristics cannot be effectively improved in high density recording at the present time if SQ in the perpendicular direction is not smaller, a magnetic layer thickness is not thinner and the particle size of magnetic substances is not smaller.
In addition, to obtain the effect with MR heads sufficiently, not only magnetic characteristics but also head touch should be taken into consideration. Therefore, both magnetic characteristics and head touch should be taken into consideration.
That is, a magnetic recording medium which is low in noise and excellent in high density characteristics has been desired even when a conventionally used coating-type magnetic recording medium which is excellent in productivity and inexpensive is combined with an MR head.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a magnetic recording medium for high density recording which is markedly improved in electromagnetic characteristics, in particular, high density recording characteristics.
The present invention is a magnetic recording medium comprising a support having provided thereon a magnetic layer containing mainly a ferromagnetic powder and a binder, wherein the ferromagnetic powder is a hexagonal ferrite powder having an average tabular diameter of from 15 to 40 nm, the perpendicular factor of squareness ratio SQ of the magnetic layer is from 0.1 to 0.55, the specific surface area and the total pore volume per weight (i.e., mass) of the magnetic layer by a nitrogen adsorption method are from 0.1 to 50 m
2
/g and from 0.001 to 1 ml/g, and the magnetic layer thickness is from 0.02 to 0.3 &mgr;m.
The preferred embodiments of the present invention are as follows.
(1) The magnetic recording medium which is used in the reproduction using a MR head.
(2) The magnetic recording medium is a magnetic tape.
(3) The magnetic recording medium is a magnetic disc.
DETAILED DESCRIPTION OF THE INVENTION
The present inventors have found that a magnetic recording medium having a markedly improved S/N ratio in high density recording area which cannot be obtained by the prior art technique can be obtained by the above constitution, thus the present invention has been accomplished.
That is, the present invention aims to reconcile the security of magnetic characteristics with the improvement of head touch. For securing mainly the former, the present invention restricts the average tabular diameter of a hexagonal ferrite powder to 15 to 40 nm, preferably from 20 to 30 nm, the perpendicular factor of squareness ratio SQ of the magnetic layer to 0.1 to 0.55, preferably from 0.2 to 0.5, and the magnetic layer thickness to 0.02 to 0.3 &mgr;m, preferably from 0.05 to 0.15 and, at the same time, for improving mainly the latter, the specific surface area and the total pore volume per weight (i.e., mass) of the magnetic layer by a nitrogen adsorption method to 0.1 to 50 m
2
/g, preferably from 5 to 10 m
2
/g, and to 0.001 to 1 ml/g, preferably from 0.01 to 0.1 ml/g, respectively. The present invention is characterized in that the latter is particularly specified.
That is, an S/N or C/N ratio cannot be improved if the specific surface area and the total pore volume deviate from the above ranges, even when the requisites which contribute to the magnetic characteristics are satisfied.
The specific surface area and the total pore volume per weight (i.e., mass) of a magnetic layer by a nitrogen adsorption method are the values measured as follows.
The specific surface area and the total pore volume per weight (i.e., mass) of a magnetic layer are measured by a nitrogen adsorption method using a measuring apparatus Auto Sorb 1 manufactured by US QUANTA CHROME Co. Pores are measured by a BJH (Brrett. Joyner. Halenda) method and the volume and the specific surface area thereof are measured with Auto-Sorb 1. As the measuring procedure at this time, a sample is deaerated for five hours or more and then measurement is performed under a liquid nitrogen temperature with Auto-Sorb 1. The magnetic layer is peeled off from the sample after the measurement, the magnetic layer is deaerated and the mass is measured. The specific surface area and the total pore volume per weight (i.e., mass) of the magnetic layer can be obtained by dividing the specific surface area and the total pore volume by the weight (i.e., mass).
The means for restricting the specific surface area and the total pore volume is not particularly limited but it is effective to arbitrarily select calendering conditions.
The magnetic recording medium according to the present invention is described in detail below.
Magnetic Layer
A magnetic layer containing a hexagonal ferrite powder may be provided on either one side or may be provided on both sides of a support of the magnetic recording medium according to the present invention.
The magnet
Harasawa Takeshi
Noguchi Hitoshi
Saito Shinji
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-3268927