Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Reexamination Certificate
2002-01-28
2004-10-12
Resan, Stevan A. (Department: 1773)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
C428S404000, C428S405000, C428S407000, C428S690000, C428S690000
Reexamination Certificate
active
06803104
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic recording medium, non-magnetic acicular black iron-based composite particles and a process for producing the non-magnetic acicular black iron-based composite particles, and more particularly, to a magnetic recording medium having a smooth surface, a lower light transmittance, a lower surface resistively value, a low friction coefficient and an excellent running durability; non-magnetic acicular black iron-based composite particles having an excellent dispersibility in vehicle due to less amount of carbon black desorbed or fallen-off from the surfaces thereof, a more excellent blackness, a lower volume resistivity value and a well-controlled myristic acid absorption; a process for producing the non-magnetic acicular black iron-based composite particles; and a non-magnetic substrate for magnetic recording media having a smooth surface and a lower surface resistivity value.
With a development of miniaturized and lightweight video or audio magnetic recording and reproducing 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.
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 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.
With respect to short wavelength signals, a reduction in the thickness of a magnetic recording layer is also strongly demanded in order to improve the high output characteristics, especially, the S/N ratio of a magnetic recording medium. 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 base film 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 coating film depends on the surface roughness of the base film (back surface roughness) so largely as to be approximately proportional, . . . , since the magnetic coating film is formed on the base film, the more smooth the surface of the base film 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 base film with a tendency of the reduction in the thickness of the base film in response to the demand for a thinner magnetic coating film. This fact is described, for example, on page 77 of the above-described
Development of Magnetic Materials and Technique for High Dispersion of Magnetic Powder
, “ . . . Higher recording density is a large problem assigned t the present magnetic tape. This is important in order to shorten the length of the tape so as to miniaturize the size of a cassette and to enable long-time recording. For this purpose, it is necessary to reduce the thickness of a base film . . . 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. If the light transmittance of the whole part of a magnetic recording layer is made large by the production of a thinner magnetic recording medium or the ultrafine magnetic particles dispersed in the magnetic recording layer, it is difficult to detect the portion having a large light transmittance by a video deck. For reducing the light transmittance of the whole part of a magnetic recording layer, carbon black fine particles or the like is added to the magnetic recording layer. It is, therefore, essential to add carbon black or the like to a magnetic recording layer in the present video tapes.
However, addition of a large amount of non-magnetic particles such as carbon black fine particles impairs not only the enhancement of the magnetic recording density but also the development of a thinner recording layer. In order to reduce the magnetization depth from the surface of the magnetic tape and to produce a thinner magnetic recording layer, it is strongly demanded to reduce, as much as possible, the quantity of non-magnetic particles such as carbon black fine particles which are added to a magnetic recording layer.
Consequently, it has been strongly demanded to provide a magnetic recording medium capable of exhibiting a low light transmittance even when the amount of carbon black fine particles added to a magnetic recording layer thereof is reduced as low as possible. From this viewpoint, it has been strongly required to essentially improve properties of a substrate therefor.
Further, in order to reduce not only the above-mentioned light transmittance of the magnetic recording medium but also an electric resistance thereof, there has been hitherto proposed a method of adding carbon black fine particles to the magnetic recording layer.
The conventional magnetic recording medium to which carbon black fine particles are added, is described in detail below.
When a magnetic recording medium has a high surface resistivity, an electrostatic charge thereon tends to be increased, so that cut chips of the magnetic recording medium and dirt or dusts are attached onto the surface of the magnetic recording medium upon production or use thereof, and as a result, such a problem that the number of “drop-out” becomes increased, is caused.
In order to decrease the surface resistivity of the magnetic recording medium to about 10
8
&OHgr;/cm
2
, a conductive compound such as carbon black fine particles has been ordinarily added to the magnetic recording layer in an amount of not less than about 5 parts by weight based on 100 parts of magnetic particles contained in the magnetic recording layer.
However, when the amount of carbon black fine particles added or the like which cannot contribute to improvement in magnetic properties of the magnetic recording layer, is increased, the magnetic recording medium has been deteriorated in electromagnetic performance as described above, resulting in inhibiting the magnetic recording layer from being thinned.
It has been required to further enhance the performance of magnetic recording media. The magnetic recording media have been strongly required to exhibit not only high-density recording property but also improved physical properties such as runn
Hayashi Kazuyuki
Iwasaki Keisuke
Morii Hiroko
Tanaka Yasuyuki
Nixon & Vanderhye P.C.
Resan Stevan A.
Toda Kogyo Corporation
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