| 摘要 |
999,385. Magnetic structures. RADIO CORPORATION OF AMERICA. March 14, 1962 [March 31, 1961], No. 9835/62. Heading H1H. A magnetic recording medium comprises a base on which is disposed a magnetic layer consisting of a polymeric binder in which are dispersed magnetic particles each of which has a coating of a Werner-type complex compound of chromium cations and carboxylic acid radicals, this coating being compatible with the binder to ensure proper dispersion. The magnetic particles may be metallic ironγFe 2 O 3 , Fe 3 O 4 or ZnFeFe 2 O 4 . They may be acicular with a length between 0À2 and 2Á and a length to width ratio of about 6. The Werner - type complex compounds are preferably of trivalent chromium cations and radicals of carboxylic acids having the formula X-R-COOH where X is selected from the group OH, NH 2 , SH, CN, NO 2 , CF 2 H, CF 3 , H, and the halogens; and R is a radical having 1 to 16 carbon atoms selected from the group of aliphatic, cyclo-aliphatic, aromatic, mixed aliphatic-aromatic, and heterocyclic radicals which may be saturated, unsaturated, straight-chain or branched. In order to provide the coating, which may be a monomolecular layer, the particles are agitated in water and a solution of the Wernertype complex is added. The pH value is increased or the temperature is raised to cause a reaction to take place, giving a permanent bonding. The particles are then washed and dried. Coated particles are not wetted by water, but are wetted by organic solvents in which they disperse readily and do not settle. The binders specified are vinyl chloride vinyl acetate copolymers, acrylic polymers, polyamides, acrylonitrile, copolymers, polyesters, nitrocellulose, styrene-butadiene copolymers. The base may be a drum, disc or tape and may be magnetic or non-magnetic. Preferably a tape 0À25-2À5 mils is used, and comprises paper, cellulose acetate modified cellulose, stretched P.V.C. copolymers, polyamides and oriented polyethylene terephthalate. The magnetic layer may be applied by dipcoating, transfer roll coating or gravure roll coating, and the particles may be oriented by a magnetic field before drying. |
