Stock material or miscellaneous articles – Circular sheet or circular blank – Recording medium or carrier
Reexamination Certificate
2001-02-22
2004-01-27
Resan, Stevan A. (Department: 1773)
Stock material or miscellaneous articles
Circular sheet or circular blank
Recording medium or carrier
C428S336000, C428S690000, C428S690000
Reexamination Certificate
active
06682800
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic recording medium containing ferromagnetic powder as a magnetic layer and used for high density recording. In particular, the invention relates to a magnetic medium having good storage property and high resistance to damage.
As a magnetic recording medium to be used in applications such as audio device, video device and computer, a magnetic recording medium is used, which comprises a magnetic layer with ferromagnetic powder dispersed in a binder, and the magnetic layer is placed on a nonmagnetic support.
In recent years, digital recording with better recording quality and less deterioration in quality compared with conventional type analog recording has rapidly propagated also in the field of video tape recorder for home use. In general, a far larger number of signals are recorded in the digital recording compared with analog recording. Also, the recording and reproduction systems and the recording medium must be higher picture quality and better tone quality and must be produced in more compact size and space-saving design, and there are much expectations on achieving high density recording.
To achieve high density recording, it is necessary to use recording signal with shorter wavelength and to have narrower recording track. For this purpose, it is necessary to have ferromagnetic powder of finer particle size and higher filling ratio and to attain smoother surface of the medium. At the same time, it is essential to have higher writing and reading speed to and from the recording medium, and attempts have been made to improve number of revolutions of cylinder or moving speed of the magnetic tape.
In the devices and equipment using the magnetic recording medium, there have been problems in that magnetic head is often stained and contaminated due to the sliding and the contact between the medium and the magnetic head. 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. With the increase of the sliding speed between the magnetic recording medium and the magnetic head, there are now strong demands on a magnetic recording medium, which has high durability to endure high-speed sliding and has high resistance to damage.
Not only for a tape type magnetic recording medium but also for a disk type magnetic recording medium, there are demands on a magnetic recording medium for high density typically represented by Zip (Iomega Inc.), which is rotated at higher speed than the conventional type floppy disk. Also, in this type of product, there are now strong demands on a magnetic recording medium, which has high durability and high resistance to damage.
To solve these problems, it has been proposed to use a magnetic recording medium containing various types of lubricants in the magnetic layer, and there have been attempts to produce a magnetic recording medium, which contains ferromagnetic metal powder dispersed in a binder so that high durability can be provided in high density recording and to perform recording and reproduction in stable manner. Also, it has been proposed to use various types of triester or tetraester as lubricants when an ester compound is used as lubricant.
For instance, U.S. Pat. No. 4,201,809 describes the use of triester or tetraester obtained from trimethylolpropane, trimethylolethane, or pentaerythritol as lubricant. However, these products are insufficient in durability and not suitable for the use on a high density recording medium such as digital recording tape.
JP-86026134(B) discloses a magnetic recording medium, which uses triester of trimethylolpropane as lubricant. This product is also insufficient in durability and has lower electromagnetic transfer characteristics in the high density magnetic recording medium.
JP-59065931(A) describes a magnetic recording medium, which simultaneously uses diester, tetraester, and monoester together with triester of trimethylolpropane as lubricant. This product is also not satisfactory in both durability and electromagnetic transfer characteristics for high density recording.
JP-61139921(A) describes a magnetic recording medium, which uses fatty acid ester of polyhydric alcohol and phosphoric acid ester of phenoxydiethylene glycol as lubricant. This product is also not satisfactory in both durability and electromagnetic transfer characteristics in high density recording.
U.S. Pat. No. 4,696,869 discloses a magnetic recording medium, which uses ester of trimethylolpropane or ester of pentaerythritol, and monoester as lubricant. This product is also not satisfactory in both durability and electromagnetic transfer characteristics in high density recording.
U.S. Pat. No. 5,258,223 proposes a magnetic recording medium, which has higher electromagnetic transfer characteristics in the recording of short wavelength and is produced by forming a nonmagnetic lower layer and a thin upper magnetic layer. In the description as disclosed, the product is also not satisfactory in durability.
SUMMARY OF THE INVENTION
The object of the present invention can be solved by the use of a magnetic recording medium, which comprises a primer layer containing at least a nonmagnetic lower layer on a support and at least one layer of magnetic layer with ferromagnetic powder dispersed in a binder, said magnetic layer being provided on said primer layer, whereby at least one type of compounds selected from the following general formulae (1) and (2) is contained at least in the primer layer:
where
R
1
is an alkyl group with 1 to 2 carbon atoms; and
R
2
, R
3
, and R
4
each represents a hydrocarbon group having 4 to 21 carbon atoms.
Also, the present invention provides the magnetic recording medium as described above, wherein thickness of the magnetic layer is within the range of 0.05 to 1 &mgr;m.
Further, the present invention provides the magnetic recording medium as described above, wherein the medium is a disk type magnetic recording medium.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention provides a magnetic recording medium for high density recording, which has high durability and good electromagnetic transfer characteristics, and this is accomplished by the use of lubricants with specific chemical structure.
In particular, it has been found in the present invention that, when triester compound of the present invention is added to a primer layer, which comprises at least a nonmagnetic lower layer and a magnetic layer coated on it and is prepared by drying and by calender processing, it is possible to obtain a magnetic layer with very smooth surface. It was also found that the magnetic recording medium thus obtained has very high durability, particularly, high-seed durability under high temperature condition.
As the lubricant to be used in the present invention, it is preferable to use a triester compound having the following chemical formulae:
where
R
1
is an alkyl group with 1 to 2 carbon atoms; and
R
2
, R
3
, and R
4
each represents a hydrocarbon group having 4 to 21 carbon atoms.
In the magnetic recording medium of the present invention, it is preferable that it contains at least one of the lubricants expressed by the general formula (1) or (2).
In particular, it is preferable that R
1
is a methyl group or an ethyl group.
Also, R
2
, R
3
, or R
4
is preferably a hydrocarbon group having 8 to 17 carbon atoms, and these may be the same or different from each other. If R
2
, R
3
, or R
4
has less than 4 carbon atoms in the hydrocarbon group, it is too volatile. When the temperature on the magnetic recording medium is increased due to friction, the quantity of the lubricant on the surface of the magnetic layer is decreased, and the durability is decrea
Harasawa Takeshi
Hashimoto Hiroshi
Mori Masahiko
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