Magnetic recording medium

Details Magnetic recording medium Magnetic recording medium

2000-06-23

2002-11-05

Resan, Stevan A. (Department: 1773)

Stock material or miscellaneous articles

Structurally defined web or sheet

Continuous and nonuniform or irregular surface on layer or...

C428S216000, C428S323000, C428S336000, C428S690000, C428S690000, C428S690000, C428S900000

Reexamination Certificate

active

06475598

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a magnetic recording particulate medium which comprises a flexible support having provided thereon a magnetic layer comprising a ferromagnetic powder and a binder, which exhibits a high output and a good C/N ratio under high-density recording and suitable for recording and reproducing digital signals at high densities.
2. Description of Related Art
In recent years, a recording wavelength tends to be shorter along with high densification, and if the thickness of the magnetic layer is thick, the output tends to be lowered, thereby raising problems such as a self-degaussing loss during recording and a thickness loss during reproducing. Therefore, a magnetic layer is tried to be thinner, but the influence of a nonmagnetic support may easily appear on the surface of the magnetic layer when the magnetic layer having a thickness equal to or less than 2 &mgr;m is directly applied to a support, and a deteriorating tendency in electromagnetic characteristics or dropouts is seen.
To solve such problems, there has been proposed a method for forming a thin thickness magnetic layer and a nonmagnetic layer under the magnetic layer on a nonmagnetic support, by using a simultaneous multilayer coating technique as well as a concentrated coating liquid for the magnetic layer as disclosed in Japanese Unexamined Patent Publication (KOKAI) Showa No. 63-191,315 and Japanese Unexamined Patent Publication (KOKAI) Showa No. 63-187,418, thereby obtaining a magnetic recording medium having an improved electromagnetic characteristics.
In the recent digital VCR systems for consumer use or the like, medium noises are required to be further reduced in a magnetic recording particulate medium. It is known that, in the digital VCR systems for consumer use, surface roughness of a wavelength pitch of around 4 &mgr;m has an influence on the medium noises. Due to the demands for high output and overwright (O/W) aptitude, the magnetic layer of the tape used for the digital VCR system for consumer use has become thinner to be around 0.1 &mgr;m (for example, Japanese Unexamined Patent Publication (KOKAI) Heisei No. 11-185,240). An influence of a magnetic layer on the surface property of the magnetic layer (for example, aggregation, or orientation disorder of the magnetic powder, and the like) becomes small because of a thinner magnetic layer. In contrast, the surface property of the lower layer (nonmagnetic layer) strongly influences the surface property of the magnetic layer. In order to make the surface property of the lower layer nonmagnetic layer smooth, the following methods have been known: a method using acicular particles as the nonmagnetic powder accompanied by the lower layer described in Japanese Unexamined Patent Publication (KOKAI) Heisei No. 4-325,915, a method using squamiform and plate-formed particles as the nonmagnetic powder accompanied by the lower layer described in Japanese Patent No. 2,698,770, and the like. However, with those methods, it was still difficult to reduce the roughness of a wavelength pitch from several micrometer to several decades of micrometer.
A magnetic recording tape can achieve high densification with the increased volume density, by lowering the tape thickness, that is, by making the tape length longer. However, in a magnetic recording particulate tape having the lower layer (nonmagnetic layer) as that of the present invention, the support thickness has been required to be thinner than that of a magnetic recording film tape (or what is called ME tape), in which a magnetic recording layer comprises a vacuum deposited cobalt alloy. As the supports are being thinner, high strength supports stretched in a width direction (TD) are getting in use from the viewpoint of securing a head touching or a running durability. However, such supports, if having micro damages, are easily broken at a coating, calendering, or slitting step, with the result that the production yields are worsen, raising problems in terms of productivity.
From these viewpoints, as for the magnetic recording tapes having a lower layer (nonmagnetic layer), it has been highly required to make the lower layer thinner. It should be noted, however, that when the lower layer is made thinner for a layer structure as described in Japanese Unexamined Patent Publication (KOKAI) Heisei No. 4-325,915 or Japanese Patent No. 2,698,770, a calender molding property would be lowered; or it would be affected by projections on the base surface, aggregations in the upper and lower layers, or additives such as an abrasive and the like, thereby the magnetic layer surface becomes rough, resulting in low output and high noises. Especially, the above phenomenon noticeably appears when the lower layer ranges from 0.1 to 0.5 &mgr;m.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a magnetic recording particulate medium, having a thickness of a magnetic layer equal to or less than 0.3 &mgr;m and a total thickness adding up the magnetic layer and a nonmagnetic layer equal to or less than 1.0 &mgr;m, exhibiting a high C/N ratio in high-density magnetic recording, and excelling in running durability.
The invention relates to a magnetic recording medium comprising, on either side of a flexible nonmagnetic support, a nonmagnetic layer containing a nonmagnetic powder and a binder and a magnetic layer containing a ferromagnetic powder and a binder in this order, characterized in that said magnetic layer has an average thickness of from 0.01 to 0.3 &mgr;m and a total average thickness of said magnetic layer and said nonmagnetic layer is from 0.1 to 1.0 &mgr;m, and a number of projections having a height equal to or higher than 20 nm , measured with an AFM (atomic force microscope), on the magnetic layer surface is equal to or less than 100 pieces per 30 &mgr;m×30&mgr;m square as well as a PSD (Power Spectrum Density) of the magnetic layer surface in the wavelength of from 1 to 5 &mgr;m measured with the AFM is equal to or less than 0.2 nm
2
.
In the magnetic recording medium according to the present invention, it is preferred to contain, in at least one of said magnetic layer and said nonmagnetic layer, a diester compound as shown in the following formula (1).
(In the formula, R
1
and R
2
represent hydrocarbon groups having a carbon number of from 7 to 12; R
3
and R
4
represent alkyl groups having a carbon number of from 1 to 6.)
DESCRIPTION OF THE PREFERRED EMBODIMENTS
One of the characteristics of the magnetic recording medium according to the present invention is that the average thickness of the magnetic layer is from 0.01 to 0.3 &mgr;m and the total average thickness of the magnetic layer and the nonmagnetic layer is from 0.1 to 1.0 &mgr;m.
In the case of recording and reproducing with a conventional magnetic induction head, if the magnetic layer is formed as thin as mentioned above, a magnetization amount becomes small, and are production output is lowered In the case of reproducing with an MR (magneto resistive) head, however, since sensitivity is sufficiently high, a sufficient output can be obtainable and a resolution property, which is an advantage of the thin magnetic layer, can be improved. In other words, by making the average value d of the thickness of the magnetic layer equal to or higher than 0.01 &mgr;m, required magnetism can be secured, and by making the average value d equal to or less than 0.3 &mgr;m, the resolution property can be enhanced, thereby the C/N ratio in using the MR head can be improved. Particularly, the average value d of the thickness of the magnetic layer preferably ranges from 0.01 &mgr;m to 0.2 &mgr;m, and more preferably from 0.01 &mgr;m to 0.1 &mgr;m, from the viewpoint of improvement of the C/N ratio with the MR head.
By making the total average thickness of the magnetic layer and the nonmagnetic layer in the range of from 0.1 to 1.0 &mgr;m, a support can be relatively thick, thereby productivity is improved and cost is reduced. Also, because a tape can be thin, the volume recording den

Affiliated with

Also associated with

Rating

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.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2950716