Magnetic recording medium

Abstract

There is provided a magnetic recording medium which comprises a substrate, a magnetic layer on one surface of a substrate and a backcoating layer on the other surface of the substrate, wherein the magnetic layer contains a magnetic metal powder having a major axis of not larger than 0.2 mum and an inorganic powder having a Mohs' hardness of at least 5, and the backcoating layer contains an inorganic powder having a particle size smaller than the size of the major axis of the magnetic metal powder and which has sufficiently reduced noise at high density recording and high output required in, for example, a small size video tape with high picture quality, the magnetic recording medium in the form of a magnetic tape having a total thickness of not larger than 14 mum inclusive of the substrate, the magnetic layer and the backcoating layer, and reliably maintained not to increase the noise after long term storage.

Description

BACKGROUND OF THE INVENTION1. Field of the InventionThe present invention relates to a magnetic recording medium with reduced noise at high density recording and high Output which are required in, for example, a small size video tape with high picture quality. In particular, the present invention provides a magnetic recording medium, such as a magnetic tape, which has a magnetic layer and a substrate, a backcoating layer having a total thickness of not greater than 14 .mu.m used in a wound form, such that the noise does not increase after long term storage.2. Description of the Related ArtIn general, a magnetic recording medium comprises a substrate made of, for example, a polyester film and a magnetic layer formed on a surface of the substrate by applying a magnetic paint which comprises a magnetic powder, a binder, inorganic powder, a lubricant and the like dispersed in an organic solvent and drying it. In particular, in case of a video tape, a backcoating layer comprising a binde...

AI Technical Summary

Benefits of technology

It has been determined that the affects on the magnetic and backcoating layer depends not only on the hardness of the particles contained in the layers but also on particle size, and that the reinforcing effect of the particles is decreased when the particle size is smaller than a specific size. In view of this fact, it has been further found that in order to prevent damage of the surface of the magnetic layer by the inorganic powder having a Mohs' hardness of 5 or higher, which is contained in the backcoating layer when the medium is wound, the inorganic powder in the backcoating layer should have a particle size smaller than a major axis of the metal magnetic powder.

Second, to improve the running properties, the backcoating layer should contain carbon black. This is disclosed in Japanese Patent Kokai Publication No. 8328 / 1987 which proposes improvement of running durability of the magnetic recording medium by the addition of fine carbon black having a particle size of from 10 to 30 m.mu. and coarse non-magnetic powder having a particle size of 200 to 500 m.mu. to the backcoating layer whereby increase of drop out is prevented.

Problems solved by technology

However, this patent literature is silent on the relationship between the primary particle size or particle size of agglomerates of the carbon black and the major axis size of the ferromagnetic metal powder in the magnetic layer, or does not investigate the relationship between the the primary particle size or particle size of agglomerates of the carbon black and the noise against the signal having a frequency corresponding to the recording wavelength of 0.8 .mu.m or less when the ferromagnetic metal particles have a small particle size.