Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Physical dimension specified
Reexamination Certificate
2002-10-29
2004-01-13
Pianalto, Bernard (Department: 1762)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Physical dimension specified
C427S128000, C428S690000, C428S690000, C428S690000, C428S900000
Reexamination Certificate
active
06677036
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for producing a magnetic recording medium, and to the magnetic recording medium. In particular, the invention relates to a method for producing a magnetic recording medium for high-density recording having a thin-layer magnetic layer, and to the magnetic recording medium obtained by that method.
BACKGROUND OF THE INVENTION
Magnetic recording media each comprising a non-magnetic support having provided thereon a magnetic layer in which a ferromagnetic powder is dispersed in a binder have been widely used as magnetic recording media such as (disks and tapes) for computers. In recent years, in magnetic recording field, practical application has advanced from the conventional analog recording to the digital recording in which recording is less deteriorated. However, the digital recording generally requires recording of many signals, compared to the analog recording. Moreover, read-write apparatus and recording media used are required to be miniaturized and decreased in space occupied thereby, as well as they are required to have high image quality and high sound quality. Accordingly, higher density recording is required.
In order to achieve high-density recording, recording signals are shortened in their wavelength and recording tracks are narrowed, so that the recording media are required to be more improved in electromagnetic characteristics. In order to improve the electromagnetic characteristics, various methods such as improvements in magnetic characteristics of the ferromagnetic powders, reductions of the powders to fine particles, high filling of the powders and ultra smoothing of surfaces of the media have been proposed. However, these techniques have not been sufficient to recent increases in recording density.
On the other hand, when the recording wavelength is further shortened, an increase in the thickness of a magnetic layer makes larger the problems of self-demagnetization loss in recording and thickness loss in reproduction. Further,in order to avoid saturation of a reproducing head, the thickness of a magnetic layer has been decreased. However, when the magnetic layer is thinned to about 0.1 &mgr;m or less, the influence of a non-magnetic support becomes easy to appear on a surface of the magnetic layer, and the tendency of the electromagnetic characteristics to deteriorate and the tendency of the error rate to increase are observed.
In order to reduce noise, it is important to decrease the size of magnetic substances, and ferromagnetic metal powders having a length in the long axis of 80 &mgr;m or less or fine ferromagnetic hexagonal ferrite powders having a tabular diameter (plate size) of 40 nm or less have been used. However, such fine granular ferromagnetic powders easily aggregate, so that it has been very difficult to obtain good dispersibility, compared to relatively large ferromagnetic powders which have hitherto been used. Further, when the dispersibility of the ferromagnetic powders is poor, the ferromagnetic powders aggregate to be liable to form minute projections on surfaces of the magnetic layers. The use of an MR head has also raised the problem of thermal asperity caused by these minute projections.
SUMMARY OF THE INVENTION
An object of the invention is to provide a method for producing a magnetic recording medium excellent in electromagnetic characteristics, suppressed in the occurrence of thermal asperity and suitable for high-density recording, and the magnetic recording medium.
The object of the invention is attained by a method for producing a magnetic recording medium of the following constitution:
1. In a method for producing a magnetic recording medium comprising providing at least one magnetic layer by applying a magnetic coating obtained by dispersing at least a binder and a ferromagnetic hexagonal ferrite powder, the method is characterized in that the binder is at least either of
(a) a binder containing 0.2 to 0.7 meq/g of at least one polar group selected from —SO
3
M, —OSO
3
M, —PO(OM)
2
, —OPO(OM)
2
and —COOM (wherein M represents a hydrogen atom, an alkali metal or ammonium) and
(b) a binder containing 0.5 to 5 meq/g of at least one polar group selected from —CONR
1
R
2
, —NR
1
R
2
and —N
+
R
1
R
2
R
3
(wherein R
1
, R
2
and R
3
each independently represents a hydrogen atom or an alkyl group), and in that
the ferromagnetic hexagonal ferrite powder subjected to the dispersion has an average tabular diameter of from 10 to 40 nm and a water content of from 0.3 to 3% by weight.
As the method f or producing the magnetic recording medium or the magnetic recording medium of the invention, preferred embodiments are described below:
2. The method for producing the magnetic recording medium described in the above (1), which is characterized in that the binder is a polyurethane (A) obtained by reacting a polyol having a cyclic structure and an alkylene oxide chain and having a molecular weight of from 500 to 5000, and a polyol having a cyclic structure and having a molecular weight of from 200 to 500 as a chain extender, with an organic diisocyanate;
3. The method for producing the magnetic recording medium described in the above (1), which is characterized in that the binder is a polyurethane (B) obtained by reacting a polyester polyol comprising an aliphatic dibasic acid and an aliphatic diol having an alkyl branched side chain and no cyclic structure, and an aliphatic diol having a branched alkyl side chain and 3 or more carbon atoms as a chain extender, with an organic diisocyanate;
4. The method for producing the magnetic recording medium described in the above (1), which is characterized in that the binder is a polyurethane (C) obtained by reacting a polyol compound having a cyclic structure and an alkyl group of 2 or more carbon atoms with an organic diisocyanate;
5. The method for producing the magnetic recording medium described in the above (1), which is characterized in that the binder is a vinyl chloride-based copolymer containing at least 75% by weight to 95% by weight of vinyl chloride monomer units;
6. The method for producing the magnetic recording medium described in the above (1), which is characterized in that the binder is an acrylic copolymer comprising 1% by weight to 75% by weight of nitrogen-containing radically polymerizable monomer units, 1% by weight to 75% by weight of aromatic ring-containing radically polymerizable monomer units and other radically polymerizable monomer units so as to give the total amount of 100% by weight;
7. A magnetic recording medium characterized in that the magnetic recording medium is obtained by the method for producing the magnetic recording medium described in any one of the above (1) to (6); and
8. The magnetic recording medium described in the above (7), which is characterized in that the magnetic recording medium is for MR head reproduction.
Although an increase in track density is indispensable for increasing the capacity of a magnetic recording medium, it becomes necessary to employ an MR head with a decrease in track width. The MR head is high in sensitivity, but it is liable to be influenced by medium noise, and the ununiformity of the dispersed state of a magnetic substance causes a noise source. Further, in the case of the MR head, a problem is encountered with regard to the occurrence of thermal asperity, which is caused by minute projections on a surface of a magnetic layer. In the invention, the suitable selection of the water content of the magnetic substance and the amount of the hydrophilic polar group of the binder has increased the amount of the binder adsorbed by the magnetic substance, and has substantially improved the level of dispersion. Improvement in dispersibility has decreased the media noise, and has also reduced the minute projections contributing to thermal asperity, resulting in the achievement of substantial improvement in recording density in combination with the MR head.
DETAILED DESCRIPTION OF THE INVENTION
The invention is described in more detail below.
In the method for produ
Noguchi Hitoshi
Saito Shinji
Yamazaki Nobuo
Fuji Photo Film Co. , Ltd.
Pianalto Bernard
LandOfFree
Method for producing magnetic recording medium and magnetic... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for producing magnetic recording medium and magnetic..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for producing magnetic recording medium and magnetic... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3244502