Process for Developing Latent Magnetic Images and use of Developing Particles Therein

1,174,573. Developing latent magnetic images. GEVAERT-AGFA N.V. 4 Nov., 1966 [5 Nov., 1965], No. 49634/66. Divided out of 1,174,571. Heading B6C. Magnetic patterns are developed by applying discrete substantially spherical solid material comprising substantially spherical magnetically susceptible metal particles coated with a thermoplastics substance. The metal may be pure, e.g. iron, or an alloy, e.g. steel, and have a high initial permeability and is formed in particles varying in size from 5 to 500 microns produced by atomizing and quenching as disclosed in Specification 1,174,572. The coating is preferably a thermoplastics resin weighing 1 to 4% of the weight of the metal core, and examples include a polyamide resin. Cellulose nitrate, ethylcellulose and a hydrogenated rosin glycerol ester, generally applied in a solvent which is subsequently evaporated. This discrete toner is preferably applied in admixture with larger carrier particles, the toner and carrier being held together by opposite triboelectric charges.