Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Including a second component containing structurally defined...
Reexamination Certificate
2002-04-24
2004-02-10
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...
C428S405000, C428S690000, C428S690000, C428S690000
Reexamination Certificate
active
06689452
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic recording medium. More particularly, the present invention relates to a magnetic recording medium having a magnetic recording layer containing surface-modified magnetic particles and/or a surface-modified filler; and a magnetic recording medium having a non-magnetic undercoat layer containing surface-modified non-magnetic particles and a magnetic recording layer on the non-magnetic undercoat layer, containing at least one selected from the group consisting of surface-modified magnetic particles, a surface-modified filler and surface-modified non-magnetic particles, which are capable of inhibiting the production of a cyclohexanone dimer in a magnetic or non-magnetic coating composition upon the production of a magnetic recording medium.
In recent years, miniaturization, lightening, recording-time prolongation, high-density recording and increased memory capacity of magnetic recording and reproducing apparatuses for audio, video or computer, have proceeded more rapidly. With such recent developments, magnetic recording medium used in these apparatuses such as magnetic tapes and magnetic disks have also been required to have a high performance and a high-density recording property.
More specifically, the magnetic recording medium have been required to have a high image definition, a high image quality and high output characteristics, especially excellent frequency characteristics, as well as enhanced storage stability, durability and running property.
In general, the magnetic recording medium has been produced by applying a magnetic coating composition prepared by blending magnetic particles and a binder resin in an organic solvent, onto a non-magnetic base film.
However, it is known that when a ketone-based solvent, especially cyclohexanone, is used as the organic solvent, a cyclohexanone diner is inevitably produced because of high surface activity of the magnetic particles present in the magnetic coating composition. As a result, conventional magnetic recording medium produced by using such a magnetic coating composition containing cyclohexanone as the organic solvent, are unsatisfactory in strength of a magnetic coating film. As to this fact, Japanese Patent Application Laid-Open (KOKAI) No. 59-172562(1984) describes that “ . . . There is a problem that a ketone-based solvent such as especially cyclohexanone tends to be dimerized during storage thereof. As a result, a magnetic layer produced by applying a coating composition containing such a solvent onto a base film tends to suffer from deteriorated strength or bleed-out . . . ”.
For this reason, it has been required to provide magnetic particles and non-magnetic particles exhibiting improved surface properties capable of preventing the production of cyclohexanone dimer in magnetic and non-magnetic coating compositions.
On the other hand, magnetic recording medium have been required to exhibit a still higher performance and, therefore, have an improved strength of coating film as well as enhanced physical properties such as running property.
The running property of magnetic recording medium is ensured by incorporating a fatty acid such as myristic acid and stearic acid (hereinafter referred to merely as “fatty acid”) in an amount of usually about 0.5 to about 5% by weight based on the weight of magnetic particles, into a magnetic recording layer generally formed as an upper layer of the magnetic recording medium, and then allowing the fatty acid to be gradually oozed onto the surface of the magnetic recording layer so as to cause the surface of the magnetic recording layer to be slidable.
When the amount of the fatty acid oozed out onto the surface of the magnetic recording layer is too small, it may be difficult to ensure a good running property of the magnetic recording medium. On the other hand, when a too large amount of the fatty acid is added to the magnetic recording layer so as to allow a large amount of the fatty acid to be oozed out onto the surface thereof, the fatty acid is preferentially adsorbed on the surface of the magnetic particles dispersed in the magnetic recording layer, so that the magnetic particles are inhibited from being absorbed in resin. As a result, it may be difficult to disperse the magnetic particles in vehicle resin. Further, an increased amount of the fatty acid as a non-magnetic component causes deterioration in magnetic properties of the magnetic recording medium. In addition, since the fatty acid acts as a plasticizer, there tend to arise additional problems such as deteriorated strength of the magnetic recording medium.
It is also known that magnetic or non-magnetic particles for magnetic recording medium are surface-treated with silane compounds in order to improve surface properties thereof (Japanese Patent Application Laid-Open (KOKAI) Nos. 51-134899(1976), 57-186302(1982), 59-172562(1984), 5-1238(1993), 8-48910(1996) and 8-120118(1996) or the like).
At present, it has been strongly required to provide magnetic particles, filler and non-magnetic particles for magnetic recording medium which are capable of inhibiting the production of cyclohexanone diner in a magnetic or non-magnetic coating composition, and improving a running property of the obtained magnetic recording medium without deterioration in dispersibility thereof. However, magnetic particles, filler and non-magnetic particles for magnetic recording medium which can fulfill these requirements, have not been obtained conventionally.
That is, in Japanese Patent Application Laid-Open (KOKAI) Nos. 51-134899(1976), 57-186302(1982), 59-172562(1984), 5-1238(1993) and 8-48910(1996), it is described that magnetic particles or metal oxide particles are surface-treated with silane compounds. However, since all of the methods are directed to wet-treatment, it may be difficult to sufficiently inhibit the production of cyclohexanone dimer in a magnetic or non-magnetic coating composition and the obtained particles tend to be deteriorated in dispersibility in vehicle, as described in Comparative Examples below.
Also, in Japanese Patent Application Laid-Open (KOKAI) No. 8-120118(1996), it is described that an inorganic filler is heat-treated together with organometallic compounds at a temperature of not less than 200° C. However, it may be difficult to sufficiently inhibit the production of cyclohexanone dimer in a magnetic or non-magnetic coating composition and the obtained particles tend to be deteriorated in dispersibility in vehicle, as described in Comparative Examples below.
As a result of the present inventors earnest studies, it has been found that by using surface-modified particles obtained by dry-mixing raw particles to be treated with a silane monomer, e.g., mechanically mixing and stirring the raw particles with the silane monomer, or mechanically mixing and stirring the raw particles with the silane compound while spraying the silane compound thereon, a magnetic recording medium are free from the production of cyclohexanone dimer in a magnetic or non-magnetic coating composition, resulting in showing an excellent coating film strength and running durability. The present invention has been attained on the basis of this finding.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a magnetic recording medium exhibiting excellent coating film strength and running durability, which is suitable as a high-density magnetic recording medium.
An another object of the present invention is to provide a magnetic recording medium containing surface-modified particles which are capable of not only inhibiting the production of cyclohexanone dimer in a magnetic or non-magnetic coating composition, but also showing an improved dispersibility in vehicle and a reduced fatty acid adsorption.
To accomplish the aims, in a first aspect of the present invention, there are provided a magnetic recording medium comprising:
a non-magnetic base film; and
a magnetic recording layer formed on the non-magnetic base film, which contains a filler, a binder resin and
Ishitani Seiji
Kamigaki Mamoru
Morii Hiroko
Nixon & Vanderhye P.C.
Resan Stevan A.
Toda Kogyo Corporation
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