Stock material or miscellaneous articles – Composite – Of polyamidoester
Reexamination Certificate
2000-03-21
2002-12-31
Resan, Stevan A. (Department: 1773)
Stock material or miscellaneous articles
Composite
Of polyamidoester
C428S690000, C428S690000, C428S900000
Reexamination Certificate
active
06500551
ABSTRACT:
The present invention relates to a magnetic recording medium comprising a nonmagnetic substrate and a magnetic layer stacked thereon and composed of a dispersion of ferromagnetic powders and a binder, which medium has ever-higher electromagnetic performance, durability and storability.
BACKGROUND ART
Magnetic recording media are now widely used in the form of recording tapes, video tapes, and floppy disks. A magnetic recording medium comprises a magnetic recording layer which is stacked on a nonmagnetic substrate, and in which ferromagnetic powders are dispersed in a binder.
The magnetic recording medium should maintain various properties such as electromagnetic performance, run durability, and run performance at high levels.
The magnetic recording medium is now required to have such excellent electromagnetic performance and, at the same time, to have good run stability. To achieve good-enough run durability, an abrasive and a lubricant are generally added to the magnetic layer.
In equipment used with a magnetic recording medium, the medium comes into sliding contact with a magnetic head. This offers a magnetic head contamination problem in which a low-molecular component of a binder in the magnetic recording medium migrates to the vicinity of the surface of a magnetic layer, adhering to the magnetic head.
Contamination of a magnetic head is a chief cause for degradation in electromagnetic performance. In equipment for high-density recording in particular, the number of rotations of the magnetic head is now on the increase. For instance, a digital video tape recorder for use at home employs a magnetic head rotating at 9,600 rpm much higher than 1,800 rpm in the case of consumer analog video tape recorders, and 5,000 rpm in the case of commercially used analog tape recorders. At such high speeds of rotation, the sliding speed between the magnetic recording medium and the magnetic head increases. The magnetic head itself is superseded by a miniature magnetic head like a thin-film magnetic head. Thus, it is strongly required to prevent contamination of the magnetic head with components resulting from the magnetic recording medium. For a high-density magnetic recording medium used in place of a floppy disk, too, it is likewise required to develop a magnetic recording medium having high strength with high reliability.
To provide a solution to such problems, it has been proposed to increase the hardness of the magnetic layer by use of a hard binder, and to use as a binder a polyurethane resin having good wear resistance and high dispersibility as well.
For instance, JP-A 61-148626 discloses a magnetic recording medium using a polyester polyurethane resin comprising a polyester diol in which at least 20% by weight of a long-chain diol component is derived from a bisphenol or its derivative and an aromatic dibasic acid or its derivative. However, dispersibility is still less than satisfactory, with a problem arising in conjunction with a storage deterioration of the medium due to hydrolysis of ester bonds.
JP-A 1-267829 discloses a magnetic recording medium using a polyether polyol polyurethane resin in which a polyether polyol having a cyclic structure accounts for at least 80% by weight of all polyol components. However, dispersibility and durability are still unsatisfactory. JP-A 4-324110 discloses a magnetic recording medium using a polyurethane resin comprising a polyester polyol including a hydrogenated dimer acid. However, dispersibility is again insufficient due to the introduction of the hydrogenated dimer acid into a polyester polyol skeleton. In consideration of the deterioration due to hydrolysis of ester bonds, such a magnetic recording medium is better than the magnetic recording medium using bisphenol but, nonetheless, is still insufficient. In particular, a magnetic recording medium with ferromagnetic powders used for a magnetic material is insufficient in terms of storability.
An object of the present invention is to provide a magnetic recording medium having ever-higher dispersibility, coating smoothness and electromagnetic performance. Another object of the present invention is to provide a magnetic recording medium that is excellent not only in medium run durability and long-term storability but also in stability with time after the preparation of a coating solution.
DISCLOSURE OF THE INVENTION
According to one aspect of the present invention, there is provided a magnetic recording medium comprising a substrate and a magnetic layer stacked thereon and composed of a dispersion of a ferromagnetic powder in a binder, wherein said binder contains a polyurethane resin 1 obtained by polymerization of a diol compound having a cyclic structure and a long-chain form of alkyl chain with a diisocyanate compound.
Preferably, the magnetic recording medium of the invention has between said substrate and said magnetic layer a lower layer comprising a dispersion of at least one of an inorganic powder and a magnetic powder in a binder while the binder in at least one of said magnetic layer and said lower layer contains polyurethane resin 1.
Preferably in the magnetic recording medium of the invention, the polyurethane resin 1 is a polyurethane resin containing as diol components a dimer diol and an aliphatic diol having a medium-chain form of alkyl branched chain.
Preferably in the magnetic recording medium of the invention, the aforesaid polyurethane resin contains 1×10
−6
to 2×10
−4
eq/g of at least one polar group selected from the group consisting of —SO
3
M, —SO
4
M, —COOM, —PO
3
M
2
, —PO
4
M
2
, a sulfobetaine group, a phosphobetaine group, a sulfamic acid group and a sulfamic acid salt group.
Preferably in the magnetic recording medium of the invention, a branched alkyl group in the aliphatic diol having a medium-chain form of alkyl branched chain has 2 to 18 carbon atoms.
Preferably, the magnetic recording medium of the invention further contains the polyurethane resin 1 and a polyurethane resin 2 comprising a polyether polyol having a cyclic structure.
Preferably in the magnetic recording medium of the invention, the aforesaid diol compound is at least one diol compound selected from those represented by the following formulae 1 and 2:
wherein:
Z is selected from a benzene ring, a naphthalene ring and a cyclohexane ring,
R
3
and R
4
are each an alkylene group having 1 to 18 carbon atoms, and
R
5
and R
6
are each an alkyl group having 2 to 18 carbon atoms.
Preferably in the magnetic recording medium of the invention, the diol compound is at least one diol compound selected from those represented by formulae 3 to 6:
wherein R
3
and R
4
are each an alkylene group having 1 to 18 carbon atoms, and R
5
and R
6
are each an alkyl group having 2 to 18 carbom atoms.
Preferably in the magnetic recording medium of the invention, the aforesaid diol compound is a dimer diol represented by formula 7:
Preferably in the magnetic recording medium of the invention, the aforesaid polyurethane resin 2 is a polyurethane resin comprising 10 to 50% by weight of a polyol containing 1 to 6 mm/g of an ether group in polyurethane, 15 to 50% by weight of a chain extender comprising a diol having a cyclic structure and an organic diisocyanate.
Preferably in the magnetic recording medium of the invention, the aforesaid magnetic layer contains polyurethane resin 1 as the binder and the aforesaid lower layer contains polyurethane resin 2 as the binder.
Preferably in the magnetic recording medium of the invention, the aforesaid binder includes polyurethane resin 1 and a polyurethane resin 3 obtained by polymerization of a polyester polyol, a chain extender and a diisocyanate compound, said polyester polyol including as a dibasic acid an aliphatic dibasic acid and as a diol component an aliphatic diol free from a cyclic structure having an alkyl branched side chain and said chain extender including as a chain extender an aliphatic diol having an alkyl branched side chain.
Preferably in the magnetic recording medium of the invention, the aforesaid diol compound is at le
Hashimoto Hiroshi
Meguro Katsuhiko
Murayama Yuichiro
Fuji Photo Film Co., LTD
Resan Stevan A.
Sughrue & Mion, PLLC
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