Stable magnetic dispersions for prodn. of recording media - by treating solvent, additives and-or binder with ion-exchanger contg. polar components of the dispersion, before adding to the dispersion

摘要

Process for prodn. of a magnetic recording medium (I), consisting of a non-magnetic base (II) on which is spread at least one magnetic dispersion contg. finely-divided magnetic pigments, polymeric binder and opt. other additives such as dispersants, wetting agents, plasticisers, lubricants, crosslinkers and accelerators, dissolved in organic solvents. Before addn. to the dispersion, the solvent and/or additives and/or binder is/are passed over ion exchanger(s) (III) which is/are fully loaded with polar gp.-contg. component(s) (IV) of the magnetic dispersion. (III) is pref. an anionic acidic or basic ion exchanger; the stability of the magnetic dispersion is routinely checked by measuring its zeta potential in organic solvent. (II) is, e.g. PET, PP, PC or CA film. Al foil, etc., and the dispersion is applied by reverse roller coating, etc.; (III) is a strongly basic ion exchanger (e.g. as described in DE-OS 3738256), Lewatit, Permutit (RTM), or a cationic exchanger; (IV) is, e.g. a poly-oxyethylene phosphate ester, dodecylphenylsulphonic acid, lecithin, alkylated fatty acid, Fe(acac)3, polymeric binder with polar gps. (e.g. as described in DE 3718957 or EP 0112924), etc.; solvent is, e.g. THF, dioxan, MEK, toluene, etc.; pref. magnetic pigment is, e.g. needle-shaped particles of Fe or Fe/Co or Fe/Ni alloy 0.1-1 micron long; binder is, e.g. VC/VAC copolymer, polyvinyl formal, PU elastomer, epoxy resin, etc.. USE/ADVANTAGE - (I) is useful for the prodn. of audio and video recording tape, etc.. The process eliminates the adverse effect of inorganic ions, organic ions and water on the stability of the magnetic dispersion.