Magnetic brush developer for electrophotography.

摘要

A magnetic brush developer for a reversal development electrophotographic process comprises a particulate toner comprising a binder resin and a particulate carrier and the toner has a strong negative chargeability and the carrier particles have a coating that comprises a resin that imparts a stronger negative chargeability than the binder resin of the toner. Preferably the particulate carrier comprises granulated magnetite particles coated with a resin in which is dispersed fluoropolymer powder and, generally, also magnetite powder or carbon black powder. The binder resin of the toner is preferably cross-linked polyester. In use, a uniform positive charge is imparted to a photoconductive insulator, the insulator is irradiated with a light image to form an electrostatic latent image and the latent image is developed and visualised by the positively charged toner in the described developer composition. Adhesion of the toner to the sleeve is avoided and print quality is maintained even during prolonged print runs.