Stock material or miscellaneous articles – Structurally defined web or sheet – Continuous and nonuniform or irregular surface on layer or...
Reexamination Certificate
2001-01-16
2002-10-22
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, C428S474400, C428S690000, C428S690000
Reexamination Certificate
active
06468628
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetic recording medium favorable to external recording media for recording computer data thereon.
2. Description of the Related Art
With the recent popularization of personal computers, magnetic recording media for external memory media for recording computer data thereon are much studied and developed. For practicable magnetic recording media for such application, much desired is increasing their recording capacity along with realizing down-sized computers for them and increasing their information processing capability. With the surroundings of magnetic recording media being much diversified these days, the requirements are increasing more than before for the reliability on the media usable in various conditions (especially, even in greatly varying temperature and humidity conditions) and the reliability on data storage in the media, and also for the reliability on stable data recording and reading even in high-speed repeated use of the media.
Ordinary magnetic recording media have a magnetic layer formed on a non-magnetic substrate of, for example, synthetic resin. For increasing the recording capacity of such magnetic recording media, some methods are believed to be effective. For example, one is to reduce the particle size of the magnetic powder to be used, or to improve the dispersibility of the magnetic powder, or to thin the magnetic layer itself. This is for increasing the recording density of the magnetic layer. Another is to reduce the overall thickness of the magnetic recording medium. In order to ensure good sensitivity of magnetic recording media (especially for high-frequency output), preferred are planarized magnetic layers, which, however, often cause some troubles of winding disorder and running failure. Some means for evading the troubles are known and are often employed in the art. For example, the surface of the substrate is roughened, or a back coat layer is formed on the substrate opposite to the magnetic layer. In particular, thin magnetic recording media are often problematic in that their self-sustenance and strength are poor. Therefore, the strength of the substrate and also the surface condition of magnetic recording media are important parameters for ensuring good running durability in repeated use of the media.
Some techniques of reducing the overall thickness of magnetic recording media in some degree are known. One example is a magnetic tape disclosed in Japanese Patent Laid-Open No. 215350/1994. One specific example of the magnetic tape disclosed herein has an overall thickness of 9.5 &mgr;m. They say therein that polyester, especially polyethylene naphthalate (PEN) is preferred for the material of the non-magnetic substrate of the magnetic tape.
We, the present inventors have studied the applicability of various types of very thin, magnetic recording media to external recording media for recording computer data thereon, and as a result, have found that even the thin magnetic tape described in Japanese Patent Laid-Open No. 215350/1994 could not still attain the intended recording capacity enough for computer data recording thereon. This is because the magnetic tape described in that laid-open specification is still thick, and the necessary length of the tape could not be housed in a predetermined cartridge. Therefore, for further enlarging its recording capacity enough for computer data recording thereon, it is necessary to further thin the tape.
On the other hand, it is known that aromatic polyamide films are preferred to conventional polyester films for non-magnetic substrates for magnetic tapes, as the former are tougher than the latter. It has been found that such an aromatic polyamide film substrate is, even when thinned, still tough and its dimension change is small even in much varying temperature and humidity conditions, and therefore the reliability on it for use in magnetic tapes for data storage thereon is good.
However, when the overall thickness of a magnetic tape having such a non-magnetic, aromatic polyamide film substrate is much reduced, the strength of the tape itself is thereby lowered, as so mentioned hereinabove, and, as a result, the tape could not ensure good running durability and will at last fail to run smoothly while used repeatedly. In addition, the tape, after having been thus fatigued, often has some negative influences on its output capacity. To solve the problems, therefore, it is necessary to improve the surface condition of the non-magnetic substrate. In particular, magnetic powder having a reduced particle size is preferred in the art, and thin magnetic layers are desired. For forming such thin magnetic layers, vacuum evaporation, ion plating, sputtering, cluster ion beam deposition and the like (these are for directly forming a magnetic layer of a magnetic metal such as Fe, Co, Ni or Cr, either alone or in the form of an alloy of such magnetic metals, on a substrate) are preferred to conventional coating. For these, the surface condition of the non-magnetic substrates and even the magnetic recording media produced must be much more optimized.
Some examples of non-magnetic, aromatic polyamide film substrates are known. For example, Japanese Patent Laid-Open No. 127523/1985, and U.S. Pat. Nos. 5,853,907 and 5,993,938 disclose magnetic recording media for which the height and the number of protrusions formed on the surface of the substrate are specifically defined. However, since the surface of the substrate has a large number of relatively high protrusions and is therefore too rough, the magnetic recording media disclosed are still problematic in that their reproduction output is lowered when the magnetic layer therein is thinned.
Japanese Patent Laid-Open No. 222837/1998 discloses a magnetic recording medium for which the surface roughness of the non-magnetic, aromatic polyamide film substrate is specifically defined. In this, the surface of the film substrate used is relatively planarized to have a surface roughness SRa of from 0.1 to 3 nm. However, there is no strict correlation between the surface roughness and the protrusions density of the film substrate. Therefore, when the magnetic layer of the medium is thinned, its surface condition could not be well controlled, and, as a result, the medium could not ensure good reproduction output. Some other examples of non-magnetic, aromatic polyamide film substrates are disclosed in Japanese Patent Laid-Open Nos. 209313/1992, 114038/1998 and 139895/1998, but all of these are also problematic like those as above.
Japanese Patent Laid-Open No. 25446/1999 and WO98/008892 disclose magnetic recording media for which the surface of the substrate is roughened to have protrusions thereon. In these, the height of each protrusions is lowered, but the protrusions density could not be controlled to a satisfactory degree for thin magnetic layers. Therefore, the reproduction output of the magnetic recording media disclosed therein is often low. In addition, the surface condition of the magnetic layer is not specifically defined therein, and its significant change is inevitable depending on the method for forming the magnetic layer.
Japanese Patent Laid-Open No. 285432/2000 discloses a magnetic recording medium for which the aromatic polyamide film substrate contains fine particles in its one surface. However, since the substrate has a large number of relatively high protrusions on its surface, the magnetic recording medium having the substrate is also problematic in that its reproduction output is lowered when the magnetic layer therein is thinned. In addition, an additional layer is sandwiched between the magnetic layer and the substrate in this medium, and therefore the overall thickness of the medium is difficult to reduce.
Japanese Patent Laid-Open No. 191213/1999 discloses a magnetic recording medium for which the ratio of the surface roughness of the film substrate to that of the medium is specifically defined. However, since the surface of the magnetic recording medium is rougher
Ito Nobuaki
Sueoka Masanori
Tsukuda Akimitsu
Kubovcik & Kubovcik
Resan Stevan A.
Toray Industries Inc.
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