| 摘要 |
<p>In a recording layer comprising acid adsorbing magnetizable particles of materials such as acicular g -Fe2O3, CrO2, metals or metal alloys dispersed in a polymeric binding agent, a strong physical bond between the particles and the binding agent is obtained by adsorbing on to the particles a dispersing polymer having acid groups and lipophilic structural units, the dispersing polymer being cross-linked with the polymeric binding agent. The two polymers, together with a suitable solvent and the magnetizable particles are ground together in a ball mill and the resulting dispersion is applied as a layer to a polyethylene terephthalate support, e.g. by means of a doctor knife. The dispersion preferably incorporates as a binding agent a polymer which can be hardened by the influence of an acid catalyst. In one example, a subbing layer of copoly-(acrylonitrile/vinylidene chloride) (5/95) is first applied to the support and the magnetizable particles are aligned in a magnetic field, the recording layer being subsequently dried and calendered; infra-red radiation is used to cure the binder. A coating of paratoluene sulphonic acid dissolved in methanol may be applied to the dried layer then dried, and is said to render the layer insoluble and very wear-resistant at its surface. Dispersing polymers containing acid groups and hydroxyl groups may be made by reacting diethyl phosphite, phthalic anhydride, or chlorosulphonic acid in anhydrous benzene, with the polyester resulting from the condensation of adipic acid, orthophthalic acid and trimethylolpropane, or by reacting a polyethylene glycol with trimellitic anhydride (forming the monoester). Details of these preparations are given. Copoly-(vinyl alcohol/ methacrylic acid) and linear or branched polyesters containing acid groups are also stated to be suitable as dispersing polymers. Binding agent polymers include partially hydrolysed copoly-(vinyl chloride/vinyl acetate), polyvinylbutyral, and a polyesteramide modified with a polyisocyanate. Appropriate solvents for the preparation of the magnetizable layer include methyl ethyl ketone, ethanol, and 1,2-dichloroethane.</p> |
