Stock material or miscellaneous articles – Structurally defined web or sheet – Continuous and nonuniform or irregular surface on layer or...
Reexamination Certificate
2000-12-11
2003-08-19
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, C428S409000, C428S425900, C428S690000, C428S690000, C428S690000, C428S690000, C428S690000, C428S900000
Reexamination Certificate
active
06607806
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a magnetic recording medium which shows less abrasion of a head and an excellent traveling property and durability.
BACKGROUND OF THE INVENTION
In VTR and computer drive in recent years, the increase of data transfer rate by increasing the relative speed of a magnetic recording medium to a magnetic head has been advanced conjointly with the improvement of recording capacity. For increasing recording capacity, the improvement of recording density is necessary, hence a magnetic recording medium which is excellent in electromagnetic characteristics is demanded. Of the systems which have achieved the realization of higher capacity and the increase of data transfer rate, above all, VTR for broadcasting mounts expensive assembled heads. Since the relative speed of head/tape of such a system becomes high correspondingly to the increase of data transfer rate, the abrasion of a magnetic head has a great influence on the maintenance fee and running cost of the system. Therefore, a magnetic recording medium which shows less abrasion of head and a longer life of head has been strongly desired.
In general, when head abrasion is reduced, still durability and the resistance to head staining are also lowered in many cases. Various methods are known for reducing head abrasion, e.g., a method of changing the kind of the abrasive in a magnetic layer to one having lower abrading property, a method of reducing the amount of an abrasive, a method of adjusting the surface oxide layer composition of a ferromagnetic metal powder, a method of optimizing the kneading strength at the time of producing a magnetic solution, and a method of increasing the amount of a lubricant. However, these methods cannot fundamentally improve the above trade-off relationship, therefore the above demand cannot be satisfied.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a magnetic recording medium which shows less head abrasion and is excellent in still durability and resistance to head staining.
The present invention has been achieved by a magnetic recording medium comprising a support having provided thereon at least one magnetic layer comprising a ferromagnetic alloy powder with Fe as a main component dispersed in a binder, wherein the scratch depth of the surface of the magnetic recording medium is from 370 to 460 nm, the surface lubricant index of the magnetic recording medium is from 4 to 11, and preferably the average long axis length of said ferromagnetic alloy powder is from 30 to 150 nm.
DETAILED DESCRIPTION OF THE INVENTION
The object of the present invention, i.e., the improvement of head abrasion and still characteristics, can be attained by controlling the scratch depth of the surface of a magnetic recording medium to from 370 to 460 nm and the surface lubricant index of a magnetic recording medium to from 4 to 11.
The surface scratch depth of a magnetic recording medium can be obtained by scratching the surface of a test sample to make a streak on the surface of a magnetic recording medium with HEIDON scratch tester and measuring the depth of the streak with an optical profiler: TOPO-3D (a product of WYKO Co., U.S.A.). The surface of a magnetic recording medium in the present specification is the surface of the side on which a magnetic layer is provided.
If the scratch depth of a magnetic recording medium exceeds 460 nm, the coated layer becomes soft and scratched powders are generated due to sliding with a magnetic head, as a result, resistance to head staining is deteriorated and clogging of a head is liable to occur. While if the scratch depth is less than 370 nm, the coated layer becomes hard and brittle, still durability is deteriorated.
For controlling the scratch depth, e.g., a method of optimizing three component ratio of binder resins (a vinyl chloride resin/a polyurethane resin/a hardening agent), a method of optimizing P/B ratio (the ratio of an inorganic powder such as a magnetic substance and a binder resin), a method of increasing the dispersing property of a magnetic powder by using a resin to which a polar functional group has been introduced, or a method of heightening elastic modulus and glass transition point (Tg) of a binder resin can be utilized. It is also possible to control scratch depth by changing calendering moldability by the prescription amount of a lubricant. Further, scratch depth can be controlled by a method of changing the main agent and the amount of a solvent for kneading to optimize the degree of kneading at the time of preparing a magnetic coating solution, a method of changing calendering conditions such as temperature, pressure and the hardness of a calender roll, and a method of introduction of a metal calender roll.
A surface lubricant index of a magnetic recording medium is an index showing the amount of a lubricant on the surface of a medium. A substance on the surface can be measured by Auger electron spectroscopy. An element existing in the depth of several tens angstrom (Å) from the surface can be analyzed by Auger electron spectroscopy, and it is possible to know the substance present on the extreme surface and the stoichiometric relationship.
In the case of a magnetic recording medium, the amounts of the lubricant and the binder resin present on the surface of a magnetic layer can be expressed by the ratio of the amount of C element resulting therefrom to the amount of Fe element resulting from the magnetic substance (C/Fe=A). A surface lubricant index is expressed as A/B by obtaining the ratio of the amount of C element (the binder component on the surface), which is measured after removal of lubricant from the recording medium, to the amount of Fe element (C/Fe=B).
The removal of a lubricant from a recording medium can be effected by immersing a medium in n-hexane to extract and remove the lubricant not adsorbed onto the magnetic substance, and then subjecting the lubricant adsorbed onto the magnetic substance to reaction with a silylating agent to be derived, extracted and removed.
The surface lubricant index of the magnetic recording medium according to the present invention is preferably from 4.5 to 11, more preferably 5 to 11, particularly preferably from 4.5 to 10.5. When the surface lubricant index is smaller than 4, the head abrasion amount abruptly increases, as a result the life of a head becomes short. While when the surface lubricant index exceeds 11, the friction coefficient sharply increases and the traveling property becomes unstable.
As is apparent from the Example described later, a surface lubricant index does not necessarily correlate with the above-described scratch depth and they are each thought to be an independent variable. However, as a specific means to control a surface lubricant index, the selection of the kind and the amount of the lubricant to be extracted by n-hexane and the same means of controlling a scratch depth as described above are applied.
The lubricants which contribute to the control of a surface lubricant index are selected from among the additives described later, and fatty acids, fatty acid esters and alcohols are particularly preferably used.
The central plane average surface roughness (SRa) of the magnetic layer according to the present invention is a value obtained by the measurement by an optical profiler: TOPO-3D. SRa is generally from 0.5 to 5.0 nm in the present invention, preferably 4 nm or less, and still more preferably 3 nm or less. If SRa exceeds 5.0 nm, the spacing loss between the magnetic recording medium and the head becomes large, as a result, output reduces and noise increases, therefore, the function of the magnetic recording medium of the present invention cannot be exhibited sufficiently. If Ra is less than 0.5 nm, the magnetic layer is generally liable to be damaged by the magnetic head.
The magnetic layer of the magnetic recording medium according to the present invention generally has a coercive force (Hc) of 1.11×10
5
A/m or more, although the optimal value varies acco
Hanai Kazuko
Kato Kazuo
Ono Mikio
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