Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Including a second component containing structurally defined...
Reexamination Certificate
1998-06-10
2003-05-20
Thibodeau, Paul (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, C428S690000
Reexamination Certificate
active
06565964
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic recording medium, which has high electromagnetic transfer characteristics and high durability and comprises a magnetic layer having ferromagnetic powder and a binder dispersed in it, and the magnetic layer is placed on a non-magnetic support.
The magnetic recording medium is widely used in such applications as recording tape, video tape, floppy disk, etc. The magnetic recording medium comprises a magnetic layer having ferromagnetic powder and a binder dispersed in it, and the magnetic layer is laminated on a non-magnetic support.
The magnetic recording medium must be at high level in such characteristics as electromagnetic transfer characteristics, running durability, and running performance. Specifically, an audio tape for reproducing musical sound must have an ability to reproduce original sound with higher quality. A video tape must have high electromagnetic transfer characteristics such as high ability to reproduce original image or picture. The magnetic recording medium used in storage device of a computer must be able to perform high density recording with high reliability.
In addition to high electromagnetic transfer characteristics as described above, the magnetic recording medium must have good running durability. To ensure good running durability, abrasive material and lubricant are generally added in the magnetic layer.
Because of sliding and contact between the medium and a magnetic head in the device where the magnetic recording medium is used, low molecular components in the binder of the magnetic recording medium tend to migrate toward surface of the magnetic layer, and this often causes problem of magnetic head contamination when these components are attached on the magnetic head.
Contamination of the magnetic head causes deterioration of electromagnetic transfer characteristics. In particular, in the device for high density recording, number of revolutions of the magnetic head is high. In a digital video tape recorder, number of revolutions of the magnetic head is as high as 9,600 rpm, and this is much higher compared with 1,800 rpm of an analog video tape recorder for household use, and 5,000 rpm of a video tape recorder for business use. Sliding speed between the magnetic recording medium and the magnetic head is getting increasingly higher, and the magnetic head and the thin film head are designed in more and more compact size, and there are strong demands to minimize and to improve the problems of magnetic head contamination caused by components of the magnetic recording medium. Also, the magnetic recording medium used for high density recording to replace floppy disk must have high strength and high reliability.
To solve the above problems and to improve property, hard binder is used to increase hardness of the magnetic layer.
For example, according to JP-A-01263927, there are provided a first and a second magnetic layers, and a polyurethane resin comprising polyether polyol, which is selected from polyethylene glycol, polypropylene glycol or polytetramethylene glycol, is used in the first magnetic layer. However, the polyurethane resin is deposited on the surface of the second magnetic layer, and this leads to higher friction coefficient during running operation and to poor durability. Further, the polytetramethylene glycol given in the example is contained in an amount of 75 weight % or more and has low strength, and there is no description on simultaneous use with a short-chain diol.
JP-B-8260531 describes a polyurethane resin comprising polyol, which contains polytetramethylene glycol and polycaprolactone. The content of the short-chain diol is about 15 weight % when calculated from the example, and glass transition temperature (Tg) of the polyurethane resin is in the range of −10° C. to +20° C. This is lower than that of the product according to the present invention. The strength of the coating film is low, and this leads to poor durability.
Similarly, JP-A-61190717 describes a polyurethane resin, which comprises polyol containing polytetramethylene glycol and polycaprolactone and a low molecular diol of glycol ester of monohydrocarboxylic acid. This aims to obtain a product with high calender workability, and coating film is often fluidized and has low durability. There is no description on glass transition temperature (Tg). Tg of the polyurethane resin given in the example is determined as about −30° C. Accordingly, the strength of the coating film is low, and durability is not satisfactory.
JP-A-08147670 describes a polyurethane resin, which comprises polyol and short-chain diol of 5 mol % or less or diamine and diisocyanate. The content of the polyol is 0 to 5 mol %, and the content of ether is low even when polytetramethylene glycol is used. Thus, it has low adsorbing property to the magnetic support, and dispersion property is not sufficient.
JP-A-08293115 (U.S. Pat. No. 5,702,821) describes the use of a polyurethane resin, which comprises a short-chain diol having cyclic structure in an amount of 17 to 40 weight % and a polyol having ether content of 1 to 5 mmol/g in the polyurethane resin in an amount of 10 to 50 weight %, but both dispersion property and smoothness are not sufficient.
As described above, the conventional type polyurethane resin used as a binder for the magnetic recording medium lacks flexibility and does not meet the requirements such as high dispersion property, smoothness and high glass transition temperature even when it is manufactured using polytetramethylene glycol and short-chain diol.
SUMMARY OF THE INVENTION
The present invention provides magnetic recording medium, which comprises at least one magnetic layer where ferromagnetic powder and a binder are dispersed, and the magnetic layer is placed on a non-magnetic support, whereby the binder comprises a polyurethane resin obtained through reaction of polytetramethylene glycol and short-chain diol having cyclic structure or short-chain diol having a branched side chain containing two or more carbon atoms, the polytetramethylene glycol is contained in the polyurethane resin in an amount of 35 to 60 weight %, the short-chain diol is contained in the polyurethane resin in an amount of 10 to 40 weight %, and glass transition temperature of the polyurethane resin is within the range of 30° C. to 120° C.
Also, the invention provides the magnetic recording medium as described above, wherein the short-chain diol having the cyclic structure is at least one of a group of bisphenol A, alkylene oxide addition product of bisphenol A, hydrogenated bisphenol A, alkylene oxide addition product of hydrogenated bisphenol A, cyclohexanedimethanol, or cyclohexane diol.
Further, the invention provides the magnetic recording medium as described above, wherein the short-chain diol having a branched side chain containing two or more carbon atoms is at least one selected from a group of 2-ethyl-1,3-hexanediol, 2-ethyl-2-butyl-1,3-propanediol, 2,2-diethyl-1,3-propanediol, 2-ethyl-2-butyl-1,3-propanediol, 2-ethyl-2-propyl-1,3-propanediol, 2,2-dipropyl-1,3-propanediol, 2-methyl-2-propyl-1,3-propanediol, and 2,2-dibutyl-1,3-propanediol.
Also, the present invention provides a magnetic recording medium, which comprises a lower layer having ferromagnetic powder or inorganic powder and a binder dispersed in it and being placed on a non-magnetic support, and at least one layer of magnetic layers where ferromagnetic powder and a binder are dispersed, whereby at least one of the binder in the lower layer or in the magnetic layer contains the polyurethane resin described in claim
1
.
Also, the invention provides the magnetic recording medium as described above, wherein the ferromagnetic powder comprises iron as main component, and the iron contains yttrium with Y/Fe ratio of 0.5 to 10 atomic %.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the magnetic recording medium of the present invention, polyurethane resin having polytetramethylene glycol as a long-chain diol component is used as a binder in the magnetic layer
Hashimoto Hiroshi
Meguro Katsuhiko
Murayama Yuichiro
Bernatz Kevin M.
Fuji Photo Film Co. , Ltd.
Thibodeau Paul
LandOfFree
Magnetic recording medium does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Magnetic recording medium, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Magnetic recording medium will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3052496