Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Including a second component containing structurally defined...
Reexamination Certificate
2000-11-06
2002-09-03
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...
C428S425900, C428S690000, C428S690000
Reexamination Certificate
active
06444306
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic recording medium, which comprises at least one magnetic layer containing a ferromagnetic particles and a binder dispersed in it, and said magnetic layer is formed on a lower layer comprising nonmagnetic powder and a binder on a nonmagnetic support member, whereby the magnetic recording medium has good electromagnetic transfer characteristics and high, durability.
Magnetic recording medium is now widely used in applications such as tape for sound recording, tape for video recording, or floppy disk. In a magnetic recording medium, a magnetic layer comprising ferromagnetic powder dispersed in a binder is formed on a nonmagnetic support member.
The magnetic recording medium must be at high level in electromagnetic transfer characteristics, running durability and running performance characteristics. That is, in an audio tape used for recording and reproducing music, higher reproduction ability to reproduce original sound is required. In a tape for video recording, high electromagnetic transfer characteristics are required such as high ability to reproduce original image.
In addition to high electromagnetic transfer characteristics as described above, the magnetic recording medium must have high running durability. In order to maintain high running durability, abrasive material and lubricant are generally added in the magnetic layer.
In a device or an equipment where the magnetic recording medium is used, the magnetic recording medium slides on and comes into contact with a magnetic head. As a result, lower molecular components in the binder of the magnetic recording medium are floated up near the surface of the magnetic layer and are attached to the magnetic head, i.e. staining occurs on the magnetic head.
The staining on the magnetic head causes deterioration of the electromagnetic transfer characteristics. In particular, in case of a device for high density recording, number of revolutions of the magnetic head is increased. In a digital video tape recorder, the number of revolutions of the magnetic head is usually 9600 rpm, and this is much higher compared with 1800 rpm in an analog video tape recorder for home use and 5000 rpm in a tape recorder for business use. The rate or the speed of sliding of the magnetic recording medium on the magnetic head is increased. Small size magnetic head is now used such as thin film head, and there are now strong demands on the improvement or the elimination of staining on the magnetic head caused by the components of the magnetic recording medium.
As one of the methods to solve the above problems, JP-05070545(A) describes a magnetic recording medium, in which polyurethane polyol with chains extended via urethane bonds is used, and polyurethane with polyurethane polyol resin with weight average molecular weight of 20,000-200,000 and with polyether of SO
3
M group is used as a binder.
Also, JP-08165372(A) describes a binder for magnetic recording medium, which comprises resin such as polyurethane resin containing sulfamic acid (salt) group.
Further, JP-09265623(A) describes the use of a magnetic recording medium, which comprises a vinyl chloride type polymer, a polyurethane resin containing sulfamic acid metal salt, and a hardening agent.
In these patent publications, polyester polyol or polyether polyol generally known is used, but there are problems in that dispersion property is not sufficiently high because ester bond or ether bond exerts action and decreases solubility in solvent. On the other hand, polyester is disadvantageous in that it is susceptible to hydrolysis and this decreases the strength of the coating film.
JP-09069222(A) describes a magnetic recording medium, which uses a binder comprising a short-chain diol with cyclic structure, a long-chain polyether polyol and a polyol containing polar group.
However, this uses polyether type substances as the long-chain polyol, and higher durability is required to maintain the strength of the coating film. The ether bond has a problem in heat-resistance at high temperature.
Further, JP-04324110(A) proposes a binder for magnetic recording medium comprising polyurethane resin using polyester polyol, which contains hydrogenated dimer acid as essential component. However, because polyester polyol is used, ester bonds are hydrolyzed during long-term storage, and the strength of the coating film is decreased.
A magnetic recording medium, which comprises polyurethane resin containing dimer diol as diol component, is proposed in JP-11096539(A). Ethylene oxide addition product of sulfoisophthalic acid is used to introduce polar group into polyurethane. Because this has hydrophilic property and has low solubility in organic solvent such as toluene, cyclohexanone, etc., reaction rate with other diisocyanate is decreased. As a result, polar group components are not evenly distributed to the binder, and improvement should be made to increase adsorption to the magnetic material and to increase the dispersion property.
It is an object of the present invention to provide a magnetic recording medium, which has high dispersion property, high smoothness in the coating film and good electromagnetic transfer characteristics. It is another object of the invention to provide a magnetic recording medium having high running durability.
SUMMARY OF THE INVENTION
To attain the above objects, the present invention provides a magnetic recording medium, which comprises at least one magnetic layer, said magnetic layer containing ferromagnetic powder and a binder and placed on a nonmagnetic support member, whereby said binder contains a polyurethane resin, using a diol compound having a cyclic structure and a long-chain alkyl chain, and a polyol with weight average molecular weight (Mw) of 400-5000 and having at least one type of polar group selected from the following groups:
—SO
3
M, —SO
4
M, —PO
3
M
2
, —PO
4
M
2
, —NHSO
3
M, >NSO
3
M, and —COOM
where M represents hydrogen, at least one type of alkali metal of potassium, sodium or lithium, and an organic amine containing at least one type of alkylamine or alkanol.
Further, the present invention provides a magnetic recording medium as described above, wherein said diol compound is at least one type selected from Formula 1 or Formula 2:
where Z is selected from benzene ring, naphthalene ring and cyclohexane ring;
R
3
and R
4
each represents an alkylene group containing 1-18 carbon atoms; and
R
5
and R
6
each represents an alkyl group containing 2-18 carbon atoms.
Also, the present invention provides a magnetic recording medium as described above, wherein said diol compound is at least one type selected from Formula 3-Formula 6:
where Z is selected from benzene ring, naphthalene ring and cyclohexane ring;
R
3
and R
4
each represents an alkylene group containing 1-18 carbon atoms; and
R
5
and R
6
each represents an alkyl group containing 2-18 carbon atoms.
Further, the present invention provides a magnetic recording medium as described above, wherein said diol compound is a dimer diol expressed by Formula 7:
The present invention further provides a magnetic recording medium as described above, wherein a layer containing magnetic powder or inorganic powder and a binder is provided between said nonmagnetic support member and said magnetic layer, and the binder in at least one of said magnetic layer or the lower layer contains said polyurethane resin.
DESCRIPTION OF THE PREFERRED EMBODIMENT
In the magnetic recording medium of the present invention, a diol component is used as polyurethane to constitute a binder, and the diol component comprises at least one type of cyclic structure selected from benzene ring, naphthalene ring, and cyclohexane ring, at least two alkylene groups containing 1-18 carbon atoms, and an alkyl group containing 2-18 carbon atoms. Because of its bending structure, it has superb solubility in solvent. This makes it possible to increase the spreading of urethane molecular chain adsorbed on the surface of magnetic material in a coating solution, and this contributes to t
Hashimoto Hiroshi
Meguro Katsuhiko
Murayama Yuichiro
Fuji Photo Film Co. , Ltd.
Resan Stevan A.
Sughrue & Mion, PLLC
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