Stock material or miscellaneous articles – Structurally defined web or sheet – Continuous and nonuniform or irregular surface on layer or...
Reexamination Certificate
1999-06-03
2003-06-17
Thibodeau, Paul (Department: 1773)
Stock material or miscellaneous articles
Structurally defined web or sheet
Continuous and nonuniform or irregular surface on layer or...
C428S323000, C428S332000, C428S402000, C428S425900, C428S522000, C428S690000, C428S690000, C428S690000, C428S690000, C428S690000
Reexamination Certificate
active
06579592
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a magnetic recording particulate medium which comprises a plastic support having provided thereon a magnetic layer comprising a ferromagnetic fine powder dispersed in a binder, and which has particularly excellent electromagnetic characteristics and durability. In particular, the present invention relates to a magnetic recording tape suitable for high density recording and reproducing of digital signals.
BACKGROUND OF THE INVENTION
Magnetic recording media are widely used as audio tapes, video tapes, computer tapes, computer discs and the like. A magnetic recording medium has become yearly higher density and the recording wavelength has become shorter and recording systems from an analog system to a digital system have been discussed.
As regarding the demand for higher density recording, a magnetic recording particulate medium formed by coating a dispersion of a ferromagnetic powder in a binder on a support has been inferior to a magnetic recording film medium, in which a magnetic recording layer comprises a vacuum deposited cobalt alloy, in electromagnetic characteristics due to low packing density of a ferromagnetic powder. However, with the improvement of the performance of ferromagnetic powders and the advancement of the coating technique of an extremely thin layer in recent years, almost the same level of electro-magnetic characteristics with those of the film medium have been achieved. Further, a magnetic recording particulate medium is superior in productivity and corrosion resistance.
Such magnetic recording particulate media are required to exhibit a high level of performances in various characteristics, such as running durability and running property, as well as electromagnetic characteristic. That is, audio tapes for sound recording/reproducing are required to have a higher degree of original sound reproducing capability. Video tapes are required to have excellent electromagnetic characteristic such as original image reproducing capability.
Magnetic recording particulate media are required to be possessed of not only such superior electromagnetic characteristics but also excellent running durability as described above. An abrasive and a lubricant are, in general, incorporated in a magnetic layer with a view to acquiring excellent running durability.
However, for obtaining excellent running durability using an abrasive, the addition amount thereof should be increased in some degree, which brings about the reduction of the packing density of a ferromagnetic powder. Further, when an abrasive having a large particle diameter is used in order to obtain excellent running durability, abrasive particles are liable to protrude excessively on the surface of the magnetic layer. Accordingly, the improvement of the running durability by an abrasive causes the deterioration of electromagnetic characteristics in some cases.
For improving the running durability by the incorporation of a lubricant such as a fatty acid and a fatty acid ester, the addition amount thereof should be increased. However, the binder is liable to be plasticized due to the increased amount of the lubricant and the durability of the magnetic layer tends to be lowered.
Further, it is a matter of course that the binder which is one of the main components of a magnetic layer also plays an important role in improving the durability and electromagnetic characteristics.
A magnetic recording particulate medium whose magnetic layer thickness is reduced by providing a nonmagnetic layer between a magnetic layer and a support is well-known. For attaining still higher recording density, a magnetic recording particulate medium having a thinner magnetic layer containing even finer ferromagnetic metal powders has been demanded. This minimization of ferromagnetic metal powders causes lowering of dispersibility leading to the degradation of the surface properties of a magnetic layer and the deterioration of electromagnetic characteristics, which makes it difficult to ensure the durability.
A binder resin having excellent durability in which a ferromagnetic metal powder and a nonmagnetic powder have excellent dispersibility and which has hardness (i.e., a high Tg and a high Young's modulus) compatible with elasticity (elongation) is most preferred as a binder for a magnetic recording particulate medium.
As a video tape suitable for a digital video cassette (DVC) of VCR for consumer use (SD specification), a tape of a magnetic recording film medium formed by a vacuum film forming technique has been nowadays put to practical use. As a tape magnetic recording particulate medium using a ferromagnetic metal powder is superior to the film medium in durability and economical point, it is very advantageous if the particulate medium is applied to DVC for consumer use. However, there is a problem such that it is very difficult with the particulate medium to stably obtain satisfactory electromagnetic characteristics, in particular, overwriting characteristics, even using a binder having excellent properties as described above.
One means for improving overwriting characteristics is to decrease coercivity (Hc) and make the thickness of a magnetic layer thin, but mere decrease of Hc leads to a decrease in saturation magnetization density of the magnetic layer, which lowers the reproduction output. That is, for improving overwriting characteristics without decreasing the reproduction output, it is necessary to increase the packing density of the magnetic fine powder contained in the magnetic layer by reducing the magnetic layer thickness or increase the saturation magnetization density of the magnetic layer by using a magnetic powder having a high degree of saturation magnetization &sgr;
s
. However, if &sgr;
s
of the magnetic powder is increased, surface properties of the magnetic layer are degraded by the orientation disturbance of the magnetic powder due to the magnetostatic interaction between magnetic powders, and thereby the output is lowered.
That is, in the particulate medium suitable for the DVC, conditions under which satisfactory durability, reproduction output and overwriting characteristics can be stably obtained have not hitherto been found yet.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a magnetic recording particulate medium having high durability and excellent electromagnetic characteristics such as reproduction output and overwriting characteristics.
The present invention can provide a magnetic recording particulate medium, in particular, a magnetic recording particulate tape for DVC (a magnetic recording particulate tape is sometimes referred to as merely a magnetic recording medium) which comprises a nonmagnetic (i.e., plastic) support having provided thereon a magnetic layer comprising a ferromagnetic metal powder dispersed in a binder, and in which the magnetic recording medium has the equal overwriting characteristics to those of the film medium, high output and low noise properties, wherein the magnetic layer has the product P of the following formula:
P=Hc×&phgr;m
(wherein Hc represents a coercivity in the in-plane machine direction of said tape expressed with a unit Oersted and &phgr;m represents saturation magnetization per unit area in the in-plane machine direction of said magnetic layer expressed with a unit Gauss·cm) in a range from 100 to 160 (Oe·G·cm) and a ratio of chlorine amount to Fe amount on a surface of said magnetic layer is equal to or less than 0.3 in terms of a Cl/Fe intensity ratio obtained by ESCA.
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, P is from 100 to 160, preferably from 110 to 150, and more preferably from 120 to 140. When the P is less than 100, reproduction output, in particular, long wavelength output, is lowered, and when the P exceeds 160, overwriting characteristics are deteriorated.
Here, it is explained below that the unit of the above &phgr;m is represented by “Gauss·cm”.
In the present invention, &phgr;m represents saturation magnetization per unit area
Doushita Hiroaki
Ejiri Kiyomi
Inaba Hiroo
Matsubaguchi Satoshi
Suzuki Masaki
Bernatz Kevin M.
Fuji Photo Film Co. Ltd
Stroock & Stroock & Lavan LLP
Thibodeau Paul
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