Magnetic recording material with improved performance - has ferromagnetic lower layer and magnetic metal upper layer with additives and particle sizes restricted to give optimum performance w.r.t. wear out

摘要

The magnetic recording material consists of a non-magnetic carrier on which multiple layers, pref. at least 2, are formed of which the lowest is a C-modified Fe-oxide and the subsequent layer is a ferromagnetic metal. The layers are either deposited on the substrate both together in wet condition or the lower layer is deposited first, and the other layer deposited on top while the first one is still wet. The powder contained in the 2 layers has an average length of the main particle axis of 250 nm of less, an average ratio of the needle-axes of 10 or less and a difference between the average length axes of 80 nm or less between the upper and lower layer. The difference in the ratios of the axes in upper and lower layer is 4 or less. The ratio of mole % Fe++/FE+++ in the lower layer is at least 5 and the lower layer contains not more than 7 wt.% soot, w.r.t. the ferromagnetic powder content, with an average prim. particle dia. of not more than 20 nm. The upper layer is pref. not more than 0.8 micron, the lower layer pref. not more than 3 micron. The powder in the lower layer pref. has a stearic-acid adsorption rate of 2-6 x 10 power(-6) mole/m2, and the powder in the upper layer a rate of at least 6x 10 power(-5) mole/m2, pref. 7-15 x 10 power(-5). The upper layer contains in addn. pref. 0.03-10 wt.%, esp. 0.05-7 wt.%, of at least one of the following organo-phosphorus cpds. (R-O)nPO(OM)3-n, (R-O)nP(OM)3-m pr (R)nPO(OM)3-n in which R is a (un)substd. alkyl-, alkenyl- or aryl-group, M is H- or an alkali-metal or -N(R1)4 in which R1 is an alkyl-group and n is 1 or 2. USE/ADVANTAGE - The formulation provides an upper magnetic layer with a high, but not too high, coercive fieldstrength which is capable of providing the high pass range performance, the lower layer provides the performance in the low-pass range. The formulation specifies particle sizes which are allow a smooth surface to be obtd. which can be lubricated efficiently with the stearic acid content without losing magnetic performance. The signal/noise ratio is high and the performance degradation with use is satisfactory