Stock material or miscellaneous articles – Structurally defined web or sheet – Continuous and nonuniform or irregular surface on layer or...
Reexamination Certificate
2001-03-14
2003-01-28
Le, H. Thi (Department: 1773)
Stock material or miscellaneous articles
Structurally defined web or sheet
Continuous and nonuniform or irregular surface on layer or...
C428S149000, C428S327000, C428S329000, C428S336000, C428S403000, C428S405000, C428S407000, C428S693100, C428S690000, C428S690000, C428S690000, C428S690000
Reexamination Certificate
active
06511733
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic recording medium, and more particularly, to a magnetic recording medium which is not only excellent in running property and durability but also capable of minimizing occurrence of drop-outs, and has a low light transmittance.
With recent tendency toward long-time recording and miniaturization of video or audio magnetic recording and reproducing apparatuses, magnetic recording media such as magnetic tapes have been increasingly and strongly required to have a higher performance, namely, a higher recording density, higher output characteristic, in particular, improved frequency characteristics and a lower noise level.
In particular, video tapes have 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, 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 with low noise 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.”
With the development of a thinner magnetic recording layer, a non-magnetic base film therefor such as a base film has also been required to have a small thickness from the viewpoints of miniaturization and long-time recording performance. As a result, such magnetic recording media suffer from deterioration in stiffness both in the machine direction and in the transverse direction, thereby causing problems concerning running property and durability thereof. 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 to 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.”
Namely, the stiffness of the magnetic recording medium has a close relationship to its restraining force for inhibiting the separation of a running tape from a guide post for regulating tape positions, or its controlling force for maintaining a constant gap between the running tape with a predetermined tension and a magnetic head for magnetic recording and reproducing so as to achieve a stable operation of the recorder. When the stiffness of the magnetic recording medium is low, the above restraining force or controlling force is weakened, resulting in occurrence of abrasion or wrinkles of the running tape, in the worse case, breaking and severe damage thereof.
Therefore, it has been strongly required to improve the running property or durability of the magnetic recording medium.
In order to improve various properties of the magnetic recording medium, it has been attempted and already put into practice to form a back coat layer comprising plate-shaped non-magnetic particles and a binder resin on the surface opposite of the non-magnetic base film to its surface on which a magnetic recording layer is provided.
However, in the magnetic recording medium having such a back coat layer, since the back coat layer of the running tape is abraded by contacting with guide members or the like within cassette halves, there tends to be caused such a defect that the frequency of drop-outs is increased due to the abrasion of the back coat layer. For this reason, it has also been strongly required to provide a magnetic recording medium which can minimize occurrence of the drop-outs by inhibiting the back coat layer of the running tape from being abraded.
Meanwhile, 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. When the light transmittance of the whole part of the magnetic recording layer becomes 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 tape end portion 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 are added to the magnetic recording layer. It is, therefore, essential to add carbon black fine particles 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 the amount 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 the magnetic recording layer is reduced.
Further, in order to reduce not only the above-mentioned light transmittance of the magnetic recording medium but also the surface resistivity 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, the frequency of “drop-outs” becomes increased.
In order to decrease the surface resistivity of the magnetic recording medium to about 108 Q/cm
2
, a conductive compound such as carbon black fine particles has been ordinarily added to the magnetic recording layer in an amount of about 5 to 20 parts by weight based on 100 parts of magnetic particles contained in the magnetic recording layer.
The larger the amount of the carbon black fine particles added to the magnetic recording layer, the lower the light transmittance of the magnetic recording medium and the smaller the surface resistivity value thereof. However, when the amount of carbon black fine particles added which cannot contribute to improvement in magnetic properties of the magnetic recording layer, is increased, the magnetic recording medium is deteriorated in high-density recording performance, and the magnetic recording layer thereof is inhibited from being thinned. Further, when an excess amount of carbon black fine particles are present in the magnetic recording
Hayashi Kazuyuki
Kamigaki Mamoru
Morii Hiroko
Le H. Thi
Nixon & Vanderhye P.C.
Toda Kogyo Corporation
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