Magnetic recording substance

DETAILED DESCRIPTION OF THE INVENTION Carbon black hitherto used in the carbon black addition method has an oil absorption of 50 to 250 ml (DBP)/100 g and a surface area of 50 to 400 m.
sup.
2 /g.
This oil absorption is defined by ml of DBP is added to 100 g of a pigment powder little by little and the state of the pigment is viewed with kneading to find a point at which it is changed from a dispersed state to a massive state, and the surface area is defined by a nitrogen absorption area.
For example, acetylene black: 230 ml(DBP)/100 g, 70 m.
sup.
2 /g; furnace black: 120 ml (DBP)/100 g, 180 m.
sup.
2 /g and channel black: 150 ml (DBP)/100 g, 400 m.
sup.
2 /g.
According to the present invention, there is provided a magnetic recording substance comprising a non-magnetic support and a magnetic recording layer provided on the non-magnetic support, the magnetic recording layer containing carbon black having a surface area of 700 m.
sup.
2 /g or more and an oil absorption of 300 ml (DBP)/100 g or more.
The quantity of this carbon black is generally 0.
5% by weight or more, preferably 1% or more to the magnetic material and the preferable ranges of the surface area and oil absorption are respectively 900 m.
sup.
2 /g or more and 320 to 400 ml (DBP)/100 g or more.
Furthermore, this carbon black has generally a particle size of about 20 m.
mu.
.
The carbon black of the present invention is considerably different from that of the prior art in surface area and oil absorption as described above.
That is to say, some large surface area carbon blacks have hitherto been known and, in the channel blacks of Columbia Carbon Co.
(USA), for example, ROYAL SPECTRA, NEO SPECTRA MARK I, NEO SPECTRA MARK II and NEO SPECTRA AG have respectively surface areas of 1125, 1065, 906 and 900 m.
sup.
2 /g, but their oil absorptions are all small, i.
e.
, 229, 219, 190 and 169 ml (DBP)/100 g.
The commonly used carbon blacks have large surface areas only and the carbon black having a large surface area and large oil absorption according to the present invention has not been used for the purpose of lowering the surface electric resistance of a magnetic layer