Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Including a second component containing structurally defined...
Reexamination Certificate
2000-02-11
2001-01-09
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...
C428S332000, C428S690000, C423S632000, C106S456000
Reexamination Certificate
active
06171692
ABSTRACT:
TECHNICAL FIELD
This invention relates to particles for use in a lower layer of a coating type magnetic recording medium having a multi-layer structure.
BACKGROUND ART
In magnetic tapes, magnetic disks and other coating-type magnetic recording media composed of a magnetic layer formed on a non-magnetic substrate, which usually consists of resinous film, by coating the substrate with a coating film of magnetic particles dispersed in a resinous binder, it is desirable for the magnetic layer to have a small thickness so as to obtain low-noise, high-output characteristics. To accomplish this, there have been proposed coating-type magnetic recording media with a multi-layer structure, which are formed between the magnetic layer and the substrate with a non-magnetic coating layer (referred to as “lower layer” in this specification) obtained by dispersing non-magnetic particles in a resinous binder.
Spherical particles of titanium oxide and iron oxide particles have so far been proposed as non-magnetic particles for use in forming the lower layer. JPA-6-215360, for instance, describes property values obtained when acicular hematite (&agr;-Fe
2
O
3
), spherical hematite (&agr;-Fe
2
O
3
), Co-&ggr;-Fe
2
O
3
, acicular TiO
2
and spherical TiO
2
are used as the non-magnetic particles of the lower layer of a multi-layer structure magnetic recording media. Likewise, JPA-6-139553, JPA-7-282443, JPA-7-326037 and JPA-7-334835 describe property values obtained when acicular &agr;-Fe
2
O
3
is used as the non-magnetic particles of the lower layer. Similarly, JPA-7-78331, JPA-7-105530 and JPA-7-182649 describe property values obtained when Co-&ggr;-Fe
2
O
3
is mainly used, and also when &agr;-Fe
2
O
3
is used, as the non-magnetic particles of the lower layer. In addition to the foregoing iron oxide particles for which specific property values are indicated, these publications also list the names of numerous other substances as being usable as the non-magnetic particles of the lower layer. Iron oxyhydroxide is included among these.
On the other hand, JPA-4-167225 teaches a multi-layer structure distinctive in that the thickness of the non-magnetic lower layer is thinner than the thickness of the upper magnetic layer, and appraises the scratching property, stiffness and head contact properties of tapes using iron oxyhydroxide particles to form the non-magnetic lower layer. JPA-6-60362, however, recommends use of acicular &agr;-Fe
2
O
3
, stating that iron oxyhydroxide is impossible to use as the particles of the lower layer because of its poor dispersibility in binder.
OBJECT OF THE INVENTION
Use of iron oxyhydroxide as lower layer particles has never actually been achieved with respect to a magnetic recording medium having a multi-layer structure. None of the aforesaid publications other than JPA-4-167225 describe specific examples of using iron oxyhydroxide (FeOOH) as lower layer particles. Actual use of iron oxyhydroxide in the manner of JPA-4-167225 has generally been considered to be impossible because of its poor dispersibility in binder, as taught by JPA-6-60362.
As such, there are still many unknowns concerning which type of iron oxyhydroxide will exhibit the intended functions when used as the particles of the lower layer of a magnetic recording medium. FeOOH is usually produced by oxidizing a suspension of Fe(OH)
2
, but it is well known that even slight variation in oxidizing conditions can result in different phases, and differences in properties and morphology. Clearly, therefore, not all known iron oxyhydroxides have the right properties for use as lower layer particles.
This invention is related to the application of iron oxyhydroxide particles as lower layer particles and is directed to clarifying how the chemical/physical properties and shape characteristics of these particles affect the surface smoothness, strength, magnetic properties and weatherability of the magnetic recording medium, and to contributing to improvement of the properties of multi-layer structure magnetic recording media through application of iron oxyhydroxide particles as lower layer particles.
DISCLOSURE OF THE INVENTION
As particles of a lower layer of a coating type magnetic recording medium having a multi-layer structure, the present invention uses iron oxyhydroxide particles that are composed of acicular particles having an average major axis of 0.01 to 0.5 &mgr;m and containing not less than 0.1 wt. % and not more than 30 wt. % of Al in the iron oxyhydroxide and that release not less than 0.1 wt. % and not more than 2 wt. % of H
2
O at 100° C. As particles of a lower layer of a coating type magnetic recording medium having a multi-layer structure, the present invention also uses iron oxyhydroxide particles that are composed of acicular particles having an average major axis of 0.01 to 0.5 &mgr;m and containing not less than 0.1 wt. % and not more than 30 wt. % of Si in the iron oxyhydroxide and that release not less than 0.1 wt. % and not more than 2 wt. % of H
2
O at 100° C. Particles containing Al and Si in combination can also be used. In this case, particles containing a total amount of Al and Si in the range of not less than 0.1 wt. % and not more than 30 wt. % are used. “Multi-layer structure” as termed here means a laminated structure comprising a non-magnetic substrate film, a non-magnetic layer of non-magnetic particles dispersed in a resinous binder formed on the substrate film, and a magnetic layer of magnetic particles dispersed in a resinous binder formed on the non-magnetic. “Lower layer” refers to the non-magnetic layer.
Those of the acicular particles according to this invention having two or more branches have their branching direction skewed toward a two-dimensional orientation so as to fall in a single plane.
When the acicular particles according the invention contain Al, the Al is preferably occluded within the acicular particles.
When the non-magnetic layer (lower layer) of the coating-type magnetic recording medium of multi-layer structure is constituted using the acicular particles according to the invention, a magnetic layer of small thickness and having no bumpiness can be uniformly formed thereon and the magnetic properties of the magnetic recording medium can be markedly improved.
REFERENCES:
patent: 5503911 (1996-04-01), Aoki et al.
patent: 5587232 (1996-12-01), Hayashi et al
patent: 5686378 (1997-11-01), Katamoto
patent: 582 472 (1993-08-01), None
patent: 4-167225 (1992-06-01), None
patent: 5262528 (1993-10-01), None
patent: 6-60362 (1994-03-01), None
patent: 6-263449 (1994-09-01), None
Aihara Yasuhiko
Hisano Seiichi
Horikawa Yoshichika
Konno Shinichi
Saito Kazuhisa
Dowa Mining Co. Ltd.
McDermott & Will & Emery
Resan Stevan A.
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