Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
2001-07-31
2003-10-07
Le, H. Thi (Department: 1773)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S690000, C428S690000
Reexamination Certificate
active
06630256
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a particulate magnetic recording medium with a total thickness equal to or less than 8 &mgr;m, and more particularly, to a magnetic recording medium having good electromagnetic characteristics and running durability. Further, the present invention relates to a magnetic recording medium, having a magnetic layer comprising a ferromagnetic powder dispersed in a binder, which is provided on a nonmagnetic support, and more particularly, a magnetic recording medium having good electromagnetic characteristics, running durability, and dimensional stability.
RELATED ART
Magnetic recording media are widely employed as recording tapes, video tapes, floppy disks, and the like.
Magnetic recording media may be divided into tape media and disk media. The configuration of both is multilayered, with a magnetic layer formed over a nonmagnetic support. However, in tape media, a backcoat layer is present when needed on the reverse surface from the surface on which the magnetic layer is provided. In disk media, magnetic layers are provided on both sides of the nonmagnetic layer support.
Magnetic recording media may be further divided into particulate magnetic recording media and vapor deposition magnetic recording media.
Generally, in particulate magnetic recording media, a ferromagnetic powder is dispersed in a binder; lubricants, abrasives, and as necessary, carbon are added; and the mixture is coated on a nonmagnetic support. In recent years, the magnetic layer has become increasingly thinner to enhance the output of the magnetic layer. Thus, magnetic recording media have been developed in which an intermediate layer (lower layer) is provided between the nonmagnetic support and magnetic layer.
In vapor deposition magnetic recording media, a vacuum vapor deposition method is employed to form a magnetic film on a nonmagnetic support. The magnetic film is formed by vaporizing and depositing a metal or alloy comprised chiefly of cobalt in an oxygen atmosphere, and as needed, forming a protective film or lubricant film over the vapor deposited magnetic film.
With respect to the magnetic recording media obtained, higher original sound reproduction capability is demanded of audio tapes used for sound recording and reproduction; good original image reproduction capability is demanded of video tapes; and high durability without loss of data is demanded of backup tapes and disks employed in computers.
To ensure such good electromagnetic characteristics and durability, magnetic materials with high Hc levels and high degrees of orientation and thin-layer coatings have been made, and protective films for the magnetic layer have been developed. Lubricants have also been developed to reduce the friction coefficient of the magnetic layer and/or backup layer.
On the recording and reproducing device side, shortening of the recording frequency wavelength and narrowing of the track width of the magnetic recording head are progressing as means of increasing the recording capacity per unit area.
For example, in cartridge-type recording media, the cartridge capacity is left unchanged, the tape is made thinner, and more tape is wound to achieve extended and high-capacity properties. A typical example is the increased capacity achieved between the DDS-2 system and DDS-3 system computer backup tapes (“Report of an Investigation into Production and Demand Trends and Technology Trends in Recording Media of the World,” published by the Japan Recording Media Industry Association, p. 97).
The above-mentioned increase in surface recording density by narrowing the track of the recording and reproducing head is progressing each year. Specifically, typical examples are the Long-Play mode in 8 mm video systems and the Zip disk system of IOMEGA corporation.
In such systems, control of the position of the recording and reproducing head and the magnetic recording medium are important. In tape media, comparatively stable running is required during running in a recording and reproducing device. Accordingly, various guides have been proposed for mounting in recording and reproducing devices to achieve stable running (Japanese Patent No. 2,976,685). Further, flanges have been mounted on the rotating guides and stationary guides to stabilize running in magnetic recording media. These flanges are generally fixed flanges. The tape running position is regulated by adjusting the height of the flange, and the precision of the flange position is important to stable running.
However, when the tape running position is regulated at a position where the edge of the tape rubs heavily, the contact pressure during running between the edge of the tape and the guide flange increases. Repeated running ends up imparting running scratches to the surface of the guide flange. As a result, these scratches damage the tape edge surface, causing the magnetic layer, intermediate layer, and/or backcoat layer coated on the nonmagnetic support to fall off.
As regards the durability of the magnetic layer surface, the development of highly durable binders and the development of lubricants for reducing the friction coefficient have progressed in recent years. As a result, products have been developed that do not fail even in systems in which the speed of the head relative to the tape is 10 m/s or greater, such as the D3 system.
However, attempts have been made to reduce the capacity of cassette cases in addition to increasing the recording density of magnetic recording media that are housed in cassette cases. Thinning of the tape itself is progressing simultaneously with increases in the density of magnetic recording medium.
With thinning of the tape, materials with increased rigidity from polyethylene terephthalate to polyethylene napththalate and further polyamides have been sequentially come the use as the nonmagnetic support. However, since the bending rigidity of the tape decreases in proportional to the cube of the thickness, it is impossible to avoid a decrease in tape strength as the tape becomes thinner, even through the use of a highly rigid materials.
Generally, when the tape runs within a recording and reproducing device for recording or reproduction, it weaves in and out. However, when the track of the recording and reproducing head is narrowed, it becomes necessary to regulate the tape running position with greater precision than has previously been the case by means of a guide flange, so that the recording and reproducing head is not prevented from tracing a straight line on the tape. In systems both employing such thinner tapes and regulating the tape running position more precisely than has previously been the case, both the durability of the magnetic layer surface and the edge of the tape are important.
Japanese Unexamined Patent Publication (KOKAI) Heisei No. 9-180173 proposes coating a protective layer on the slit end surface to increase durability. However, the coating of a protective layer on the end surface after the slit has drawbacks in that the protective solution may ooze out onto the magnetic layer during coating, increasing the cost of coating and making it impossible to provide an inexpensive tape.
To prevent edge damage from occurring during continuous repeat running in magnetic recording and reproducing devices, the support by a nonmagnetic support is significant. A nonmagnetic support (polyethylene terephthalate (PET), polyethylene naphthalate (PEN), or the like) equal to or higher than 6 &mgr;m is normally employed in a magnetic recording medium with a total thickness equal to or higher than 8 &mgr;m to achieve stable repeat running with little edge damage. By contrast, an aromatic polyamide (aramid) base is now employed instead of the polyethylene terephthalate (PET), polyethylene naphthalate (PEN), or the like, that was conventionally employed as the nonmagnetic support in recording media having a total thickness of less than 8 g m (Japanese Patent No. 2,724,581).
Further, in recording media equal to or less than 8 &mgr;m in total thickness, it is also necessary to reduce the
Miura Toshihiko
Suzuki Masaki
Takahashi Masatoshi
Takano Hiroaki
Fuji Photo Film Co. , Ltd.
Le H. Thi
Stroock & Stroock & Lavan LLP
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