Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Including a second component containing structurally defined...
Reexamination Certificate
1999-12-17
2002-10-01
Resan, Stevan A. (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Including a second component containing structurally defined...
C428S328000, C428S329000, C428S336000, C428S690000, C428S690000, C423S609000, C423S610000, C423S611000, C423S612000, C423S613000, C423S614000, C423S615000, C423S616000
Reexamination Certificate
active
06458452
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to titanium oxide particles, a substrate for a magnetic recording medium and a magnetic recording medium using the substrate. More particularly, the present invention relates to titanium oxide particles suitable as non-magnetic particles for a non-magnetic undercoat layer of a magnetic recording medium which uses magnetic particles containing iron as a main ingredient, and even more particularly, to titanium oxide particles suitable as non-magnetic particles for a non-magnetic undercoat layer of a magnetic recording medium which uses magnetic particles containing iron as a main ingredient, which show an excellent dispersibility in a binder resin, which contain only a small amount of soluble sodium salt and soluble sulfate, and have a pH value of not less than 8, a substrate for the magnetic recording medium, and a magnetic recording medium using the substrate.
With a development of miniaturized and lightweight video or audio magnetic recording and reading-out apparatuses for long-time recording, magnetic recording media such as a magnetic tape and magnetic disk have been increasingly and strongly required to have a higher performance, namely, a higher recording density, higher output characteristic, in particular, an improved frequency characteristic and a lower noise level.
Various attempts have been made at both enhancing the properties of magnetic particles and reducing the thickness of a magnetic layer in order to improve these properties of a magnetic recording medium.
The enhancement of the properties of magnetic particles will first be described.
The properties which magnetic particles are required to have in order to satisfy the above-described demands on a magnetic recording medium, are a high coercive force and a large saturation magnetization.
As magnetic particles suitable for high-output recording and high-density recording, acicular magnetic particles containing iron as a main ingredient which are obtained by heat-treating acicular goethite particles or acicular hematite particles in a reducing gas, are widely known.
Although acicular magnetic particles containing iron as a main ingredient have a high coercive force and a large saturation magnetization, since the acicular magnetic particles containing iron as a main ingredient used for a magnetic recording medium are very fine particles having a particle size of not more than 0.3 &mgr;m, particularly, 0.01 to 0.2 &mgr;m, such particles easily corrode, and as a result, magnetic characteristics thereof are deteriorated, especially, the saturation magnetization and the coercive force are reduced.
Therefore, in order to maintain the characteristics of a magnetic recording medium which uses magnetic particles containing iron as a main ingredient as the magnetic particles over a long period, it is strongly demanded to suppress the corrosion of acicular magnetic particles containing iron as a main ingredient as much as possible.
A reduction of the thickness of a magnetic recording layer will now be described.
Video tapes have recently been required more and more to have a higher picture quality, and the frequencies of carrier signals recorded in recent video tapes are higher than those recorded in conventional video tapes. In other words, the carrier signals in the short-wave region have come to be used, and as a result, the magnetization depth from the surface of a magnetic tape has come to be remarkably small.
For the purpose of high-density recording, it is necessary to maintain the output characteristics, to reduce noise, and especially, to improve the S/N ratio with respect to signals having a short wavelength as well. In a magnetic recording medium composed of a substrate and a magnetic recording layer formed on the substrate, it have been conducted to reduce the thickness of the magnetic recording layer. This fact is described, for example, on page 312 of
Development of Magnetic Materials and Technique for High Dispersion of Magnetic Powder
, published by Sogo Gijutsu Center Co. Ltd. (1982), “. . . the conditions for high-density recording in a coated-layer type tape are that the noise level is low with respect to signals having a short wavelength and that the high output characteristics are maintained. To satisfy these conditions, it is necessary that the tape has large coercive force Hc and residual magnetization Br, . . . and the coating film has a smaller thickness. . . . ”
Development of a thinner film for a magnetic recording layer has caused some problems.
Firstly, it is necessary to make a magnetic recording layer smooth and to eliminate the non-uniformity of thickness. As well known, in order to obtain a smooth magnetic recording layer having a uniform thickness, the surface of the substrate must also be smooth. This fact is described on pages 180 and 181 of
Materials for Synthetic Technology
-
Causes of Friction and Abrasion of Magnetic Tape and Head Running System and Measures for Solving the Problem
(hereinunder referred to as
Materials for Synthetic Technology
(1987), published” by the publishing department of Technology Information Center, “. . . the surface roughness of a hardened magnetic layer depends on the surface roughness of a substrate (back surface roughness) so largely as to be approximately proportional, . . . since the magnetic layer is formed on the substrate, the more smooth the surface of the substrate is, the more uniform and larger head output is obtained and the more the S/N ratio is improved.”
Secondly, there has been caused a problem in the strength of a non-magnetic substrate such as a base film with a tendency of the reduction in the thickness of a non-magnetic substrate which has been conventionally used in response to the demand for a thinner magnetic layer. This fact is described, for example, on page 77 of the above-described
Development of Magnetic Materials and Technique for Bigh Dispersion of Magnetic Powder
, “. . . Higher recording density is a large problem assigned to the present magnetic tape. This is important in order to shorten the length of the tape so as to miniaturize a cassette and to enable long-time recording. For this purpose, it is necessary to reduce the thickness of a substrate . . . With the tendency of reduction in the film thickness, the stiffness of the tape also reduces to such an extent as to make smooth travel in a recorder difficult. Therefore, improvement of the stiffness of a video tape both in the machine direction and in the transverse direction is now strongly demanded.”
The end portion of a magnetic recording medium such as a magnetic tape, especially, a video tape is judged by detecting a portion of the magnetic recording medium, at which the light transmittance is large by a video deck. As acicular magnetic particles containing iron as a main ingredient used-for high-density recording, very fine particles are used as described above. With such a tendency of the reduction in the particle size of magnetic particles, and the thickness of the magnetic recording layer and substrate, the light transmittance of the magnetic recording medium tends to be larger, and as a result, it is difficult to detect the end of the magnetic tape by the video deck. For reducing the light transmittance of the magnetic recording medium, carbon black or the like is added to the magnetic recording layer. It is, therefore, essential to add carbon black br the like to a magnetic recording layer in the present video tapes.
However, addition of non-magnetic carbon black impairs not only the enhancement of the recording density but also the reduction of the thickness of the magnetic recording layer. It is, therefore, strongly demanded that the light transmittance of a magnetic recording layer should be small even if the amount of the carbon black or the like which is added thereto is reduced to small or zero. From this point of view, improvements in the substrate are now in strong demand.
On the other hand, there is no end to a demand for a higher performance in recent magnetic recording media. With the a
Hayashi Kazuyuki
Iwasaki Keisuke
Morii Hiroko
Tanaka Yasuyuki
Nixon & Vanderhye P.C.
Resan Stevan A.
Toda Kogyo Corporation
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