Stock material or miscellaneous articles – Composite – Of polyamidoester
Patent
1984-03-01
1985-07-16
Robinson, Ellis P.
Stock material or miscellaneous articles
Composite
Of polyamidoester
427128, 427131, 360134, 360135, 360136, 252 6254, 428328, 428329, 428694, 428900, G11B 570
Patent
active
045296618
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a magnetic recording medium and, more particularly, to a magnetic recording material such as a magnetic tape which has improved durability and surface properties.
BACKGROUND ART
With rapid advance in the field of magnetic recording, further improvements in magnetic recording media are demanded than ever before. High reproduction output is required in short-wave recording, especially in a VTR magnetic recording medium. In view of this, finely dividing of magnetic particles is used to improve the S/N ratio and to make the surface of the magnetic layer smoother. However, when the magnetic powder consists of such fine particles, the coating viscosity increases during the manufacture thereof. This results in an additional problem of a degraded dispersibility of the magnetic powder.
The problem involved in an increase in the viscosity of the magnetic coating is not limited to the degradation in the dispersibility of the magnetic powder. For example, in the coating transfer step during the manufacture of the magnetic recording medium, the transfer of the coating cannot be smoothly performed. This tends to cause local retention of the coating in the transport path and to result in hardening of the coating. This may also lead to drop-out when the coating is used to form a magnetic layer. When such a coating is coated, the coating cannot be easily smoothed after being transferred onto a nonmagnetic support. As a result, a good surface property cannot be obtained. Furthermore, an increase in the viscosity of the coating provides a disadvantageous condition for a thin layer coating which has currently been developed. Thus, there are a wide range of problems which may be encountered with an increase in the viscosity of the coating in the process from the manufacture of magnetic coating to the formation of magnetic layer.
When the magnetic powder is finely divided, i.e., when the specific surface area of the powder increases, the contact interface between the magnetic powder and a coating or a binder increases. This means that an increased energy is required for dispersing the magnetic powder. This problem can be partially resolved by improving a mixing/dispersing unit. However, the degree of such an improvement is limited. In view of this, the conventional method has used a surfactant which also improves the dispersibility. However, with this method, when the amount of the surfactant added is increased for improving the dispersibility, the properties of the layer tend to be impaired. For this reason, this method has not been ideal when high-density recording and high durability which are required for current magnetic recording media, are consiered.
DISCLOSURE OF INVENTION
It is an object of the present invention to provide a magnetic recording medium wherein a resin having a polar group and a good dispersibility is mixed with a magnetic powder, in a specific molar ratio to attain a specific surface area so that any increase in a resultant coating and a degradation in the dispersibility of the magnetic powder are prevented, a rubbing-off in a drive mechanism (VTR) is prevented, and durability is improved.
In order to achieve the above object of the present invention, there is provided a magnetic recording medium having on a nonmagnetic support a magnetic layer consisting mainly of a acicular iron oxide magnetic powder and a binder, characterized in that the iron oxide magnetic powder has a specific surface area as determined by the BET method, of not less than 35 m.sup.2 /g, and the binder contains a resin which has a molecular weight of not more than 50,000 and at least one polar group selected from the group consisting of polar groups having the general formulas: ##STR2## (wherein M is hydrogen, lithium, sodium or potassium; and M.sub.1 and M.sub.2 are hydrogen, lithium, sodium, potassium or alkyl groups).
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a graph showing the relationship between the molecular weight of a polyurethane resin and the coating viscosity of a
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Hashimoto Akira
Ninomiya Yoshinobu
Robinson Ellis P.
Sony Corporation
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