Stock material or miscellaneous articles – Structurally defined web or sheet – Continuous and nonuniform or irregular surface on layer or...
Reexamination Certificate
2003-03-11
2004-10-05
Resan, Stevan A. (Department: 1773)
Stock material or miscellaneous articles
Structurally defined web or sheet
Continuous and nonuniform or irregular surface on layer or...
C428S323000, C428S329000, C428S336000, C428S690000
Reexamination Certificate
active
06800356
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a magnetic recording medium for high-density recording and reproduction more particularly, it relates to a magnetic recording medium having high durability in a reproduction system using a magnetoresistive (MR) head.
BACKGROUND OF THE INVENTION
A floppy disk drive accepting MF-2HD floppy disks is preinstalled on today's personal computers. As the volume of data to be processed, such as imaging data, is drastically increasing, the capacity of an MF-2HD floppy disk has now come to be seen as insufficient. Magnetic disks of much larger capacity than predecessors have been awaited.
In the field of magnetic tapes, too, the recent spread of office computers such as minicomputers, personal computers, and work stations has boosted studies on magnetic tapes for storing computer data as an external memory medium (i.e., backup tapes). Before magnetic tapes for this application are developed for practical use, it is keenly required to improve recording capacity of magnetic tapes for achieving high-capacity recording and medium size reduction particularly for coping with the trend toward miniaturization and data processing power enhancement of computers.
Widespread magnetic recording media comprise a non-magnetic support having provided thereon a magnetic layer containing a magnetic substance, such as iron oxide powder, Co-doped iron oxide powder, CrO
2
powder, ferromagnetic metal powder, or hexagonal ferrite powder, dispersed in a binder. Recently, a magnetoresistive (MR) head has come to be used for a hard disk drive in a system using a flexible recording medium. Because an MR head has high sensitivity to provide sufficient reproduction output, combination of an MR head and fine magnetic particles with a relatively low saturation magnetization as realizes noise reduction, leading to a high C/N ratio. For example, JP-A-10-302243 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”) discloses a magnetic recording medium containing fine barium ferrite (BaFe) particles which is adapted to use in a reproduction system with an MR head.
In addition to the use of an MR head for reproduction, it is necessary in a high recording density (particularly linear recording density) system to optimize the relationship between recording conditions and a medium. In high linear density recording, the recording head gap is usually made smaller so as to reduce the influences of recording demagnetization and bit-shift. This, however, narrows the recording magnetic field, which, in turn, impairs the overwriting performance and increases thickness loss. Further, since the magnetization reversal width becomes narrower, the influence of magnetization disturbance in the magnetization transfer region is no more negligible, resulting in S/N loss.
SUMMARY OF THE INVENTION
With the ever-increasing recording density of magnetic recording media, improvements in running stability and durability of the media have been subjects to be addressed. To accomplish the subjects, JP-A-2000-40218 proposes a magnetic recording medium having specific depressions on both the magnetic layer and the backcoating layer.
An object of the present invention is to provide a magnetic recording medium having satisfactory electromagnetic characteristics and excellent durability particularly in high-density recording regions.
As a result of extensive investigation, the present inventors have found that the above object is accomplished by a magnetic recording medium having a backcoating layer which contains a specific amount of a lubricant and has projections in a specific range of profile.
The present invention provides a magnetic recording medium having a magnetic layer containing a ferromagnetic powder and a binder on a non-magnetic support and a backcoating layer containing a non-magnetic powder and a binder on the opposite side of the non-magnetic support, wherein the backcoating layer contains 0.3 to 5% by weight of at least one of a fatty acid having 10 to 26 carbon atoms and an ester thereof, the backcoating layer has projections having a height of 100 nm or smaller as measured with an atomic force microscope (AFM), and the density of projections on the backcoating layer which have a height of 25 to 100 nm as measured with an AFM is 1000 or fewer per 90 &mgr;m side square.
The present invention provides preferred embodiments of the magnetic recording medium, in which (1) the backcoating layer has a thickness of 0.1 to 1.0 &mgr;m and/or (2) the non-magnetic powder of the backcoating layer has an average particle size of 5 to 300 nm, and the backcoating layer contains an electrically conductive powder having an average particle size of 10 to 150 nm.
DETAILED DESCRIPTION OF THE INVENTION
The magnetic recording medium of the present invention is of the type which has a backcoating layer containing a non-magnetic powder and a binder on the backside of a non-magnetic support and is characterized by a specific design of the backcoating layer.
In general, magnetic tapes for computer data storage are strongly required to have durability against repeated running as compared with video tapes and audio tapes. A backcoating layer is provided to maintain high running durability. The characteristics of the invention reside in that the backcoating layer contains 0.3 to 5% by weight of a fatty acid and/or a fatty acid ester and has projections of 100 nm or smaller in height as measured with an AFM with the density of projections of 25 to 100 nm (measured with an AFM) being 1000 or fewer per 90 &mgr;m side square.
The backcoating layer of the invention contains a non-magnetic powder and a binder and, in addition, a specific amount of a fatty acid and/or a fatty acid ester. The fatty acid preferably includes monobasic fatty acids having 10 to 26 carbon atoms and their salts with a metal, e.g., Li, Na, K or Cu. The fatty acid ester preferably includes one formed between these monobasic fatty acids and alcohols.
More specifically, the fatty acid and an ester thereof include monobasic fatty acids having 10 to 26 carbon atoms which may be saturated or unsaturated and straight-chain or branched; their salts with a metal (e.g., Li, Na, K or Cu); mono- to hexahydric alcohols having 4 to 22 carbon atoms which may be saturated or unsaturated and straight-chain or branched; alkoxyalcohols having 12 to 22 carbon atoms; mono-, di- or tri-fatty acid esters formed between a monobasic fatty acid having 10 to 26carbon atoms which may be saturated or unsaturated and straight-chain or branched and one of mono- to hexahydric alcohols having 2 to 12 carbon atoms which may be saturated or unsaturated and straight-chain or branched; and esters of a fatty acid and a polyalkylene oxide monoalkyl ether.
Specific examples of the fatty acids are capric acid, caprylic acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, elaidic acid, linoleic acid, linolenic acid, and isostearic acid.
Specific examples of the fatty acid esters are butyl stearate, octyl stearate, amyl stearate, isooctyl stearate, butyl myristate, octyl myristate, butoxyethyl stearate, butoxydiethyl stearate, 2-ethylhexyl stearate, 2-octyldodecyl palmitate, 2-hexyldodecyl palmitate, isohexadecyl stearate, oleyl oleate, dodecyl stearate, tridecyl stearate, oleyl erucate, neopentyl glycol didecanoate, ethylene glycol dioleate. Specific examples of the alcohols are oleyl alcohol, stearyl alcohol, and lauryl alcohol.
The content of the fatty acid and/or fatty acid ester in the backcoating layer is 0.3 to 5% by weight, preferably 0.5 to 4% by weight, still preferably 0.75 to 3.5% by weight. If the fatty acid and/or fatty acid ester content is less than 0.3%, the coating layer is liable to suffer from destruction starting from lubricant-starved parts, resulting in poor running durability. Too high contents plasticize the magnetic layer, resulting in film strength reduction.
The backcoating layer has on its surface projections of 25 to 100 nm high measured with an AFM at a specific density. Such proj
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-3281133