Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Including a second component containing structurally defined...
Reexamination Certificate
2000-04-25
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...
C428S403000, C428S405000, C428S690000, C428S402000, C106S287100, C106S287130
Reexamination Certificate
active
06458453
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic recording medium, and more particularly, to a magnetic recording medium having not only an excellent durability and a good electromagnetic performance, but also a low light transmittance, a small surface resistivity and an excellent surface smoothness, and a filler contained in a magnetic recording layer constituting the magnetic recording medium.
With recent tendencies of miniaturization and weight reduction of video or audio magnetic recording and reproducing apparatuses as well as long-time recording by these apparatuses, magnetic recording media such as magnetic tapes or magnetic discs have been strongly required to have a high performance, namely high recording density, high durability, good electromagnetic performance or the like.
The magnetic recording media such as magnetic tapes or magnetic discs are contacted with a magnetic head upon recording and reproduction, so that a magnetic recording layer thereof tends to be abraded, resulting in contamination of the magnetic head as well as deterioration in recording and reproducing characteristics thereof. For this reason, it has been conventionally demanded to provide high-durability magnetic recording media having a high abrasion resistance.
Hitherto, in order to enhance an abrasion resistance of the magnetic recording layer of magnetic recording media, it has been attempted to incorporate various fillers such as alumina (Al
2
O
3
), hematite (&agr;-Fe
2
O
3
) and dichromium trioxide (Cr
2
O
3
) into the magnetic recording layer.
For instance, as magnetic recording media using alumina (Al
2
O
3
), there have been proposed magnetic recording media in which &agr;-Al
2
O
3
particles containing an amorphous phase are used as a filler (Japanese Patent Application Laid-Open (KOKAI) No. 5-36059(1993)), magnetic recording media in which &agr;-Al
2
O
3
particles having a specific crystal structure are used as a filler (Japanese Patent Application Laid-Open (KOKAI) No. 7-244836(1995)) and the like; as magnetic recording media using hematite (&agr;-Fe
2
O
3
), there have been proposed magnetic recording media in which granular &agr;-Fe
2
O
3
particles are used as a filler (Japanese Patent Application Laid-Open (KOKAI) No. 61-194628(1986)), magnetic recording media in which liquid hydrocarbon and &agr;-Fe
2
O
3
particles are used (Japanese Patent Application Laid-Open (KOKAI) No. 54-70806(1979)) and the like; and as magnetic recording media using dichromium trioxide (Cr
2
O
3
), there have been proposed magnetic recording media in which acicular Cr
2
O
3
particles are used as a filler (Japanese Patent Application Laid-Open (KOKAI) No. 62-112221(1987)) and the like.
Specifically, the magnetic recording medium described in Japanese Patent Application Laid-Open (KOKAI) No. 61-194628(1986) contains magnetic particles having a specific surface area of not less than about 28 m
2
/g and granular &agr;-Fe
2
O
3
having an average particle diameter of about 0.05 to 1 &mgr;m. This magnetic recording medium is produced by dispersing a mixture composed of 300 parts by weight of Co-coated &ggr;-Fe
2
O
3
, 38 parts by weight of vinyl chloride-vinyl acetate copolymer, 24 parts by weight of polyurethane resin, 7 parts by weight of stearic acid, one part by weight of silicone oil, a prescribed amount of granular &agr;-Fe
2
O
3
having a predetermined particle size and 800 parts by weight of a mixed solvent containing methyl ethyl ketone and toluene in equal amounts, for 40 minutes using a ball mill to prepare a magnetic coating composition, and then coating a base film with the magnetic coating composition.
However, these fillers have respective inherent problems. Namely, it is known that alumina shows a poor dispersibility in binder resin. With increase in amount of alumina added, the obtained magnetic recording medium is considerably deteriorated in electromagnetic performance. Hematite particles exhibit a relatively good dispersibility in binder resin. However, in order to obtain magnetic recording media having a sufficient durability, it is required to add a considerably large amount of the hematite particles thereto, resulting in deteriorated filling percentage of magnetic particles and, therefore, poor electromagnetic performance. Further, the use of dichromium trioxide is unfavorable from environmental and hygienic viewpoints.
It is also known that when the amount of these fillers added to the magnetic layer is increased, resultant magnetic recording media are improved in durability, but deteriorated in dispersibility of magnetic particles in vehicle, thereby causing a considerable deterioration in electromagnetic performance thereof.
Accordingly, it has been strongly demanded to provide magnetic recording media containing such a filler which does not adversely affect the dispersibility of magnetic particles in vehicle even when the filler is added in an amount sufficient to impart a high durability thereto, thereby preventing the magnetic recording media from being deteriorated in electromagnetic performance thereof.
In current general-purpose video tape systems, the end position of such a magnetic tape is recognized by detecting a transparent leader tape provided at the tape end thereof using a sensor. However, with recent demands for high-density recording on magnetic recording media, the particle size of magnetic particles used therein becomes much finer, so that a magnetic recording layer containing such magnetic particles has a high light transmittance. As a result, there arises the risk of occurrence of errors upon detecting the end position of the magnetic tape. Therefore, it has been strongly required that a magnetic recording portion of the magnetic tape has a sufficiently high blackness, i.e., a low light transmittance.
Further, it has been endlessly demanded to further improve characteristics of magnetic recording media. Therefore, it is strongly required to provide magnetic recording media having not only the above-described characteristics but also a small surface resistivity, an improved running property and the like.
The reasons therefor are as follows. When the surface resistivity of magnetic recording media is large, the amount of electrostatic charge thereon is increased, so that cut chips of the magnetic recording media or dusts are adhered onto the surfaces of the magnetic recording media upon production and use thereof, thereby causing problems such as increase in drop-outs.
It is widely known that carbon black fine particles as a black filler are incorporated into a magnetic recording layer. Also, there have been proposed magnetic recording media in which black titanium (TiO) particles are used as a black filler (Japanese Patent Publication (KOKOKU) Nos. 62-21185(1987) and 62-22179(1987)), magnetic recording media in which graphite fluoride is used a black filler (Japanese Patent Application Laid-Open (KOKAI) No. 56-156930(1981)), or the like.
Also, hitherto, with the reduction in thicknesses of magnetic recording layer and non-magnetic base film of magnetic recording media, it has been variously attempted to impart good surface smoothness and large stiffness thereto by improving a substrate on which the magnetic recording layer is formed. For instance, there has been proposed a non-magnetic substrate composed of a non-magnetic base film and at least one undercoat layer formed on the non-magnetic base film. The undercoat layer is composed of a binder and non-magnetic particles dispersed in the binder, which contain iron as a main component, e.g., acicular hematite particles or acicular iron oxide hydroxide particles (hereinafter referred to merely as “non-magnetic undercoat layer”). Such a non-magnetic substrate is already put into practice (refer to Japanese Patent Publication (KOKOKU) No. 6-93297(1994), Japanese Patent Application Laid-Open (KOKAI) Nos. 62-159338(1987), 63-187418(1988), 4-167225(1992), 4-325915(1992), 5-73882(1993), 5-182177(1993), 5-347017(1993) and 6-60362(1994), or the like).
Thus, at present, it has been most strongly dem
Hayashi Kazuyuki
Ishitani Seiji
Kamigaki Mamoru
Morii Hiroko
Bernatz Kevin M.
Resan Stevan A.
Toda Kogyo Corporation
LandOfFree
Magnetic recording medium does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Magnetic recording medium, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Magnetic recording medium will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2998199