Oce-nederland B.v.

Oce-van Der Grinten N.v.

Roelof R Hendriksma

Wilhelmus J VanRhijn

Toner powders having excellent flow and non-agglomerating properties, and being readily removable from the imaging medium in use for indirect electrophotographic copying, are provided in the form of substantially spherical resin particles, containing additives or not as desired, which particles have been formed from irregularly shaped resin particles heated in a liquid dispersion containing hydrophobic silica particles smaller than 100 nanometers in diameter. The toner particles may be thus formed so as to carry on their surface or dispersed therein electrically conductive particles, such as carbon black, rendering them attractable by electrical inductance. The toner can be prepared simply by heating and stirring irregularly shaped resin particles and hydrophobic silica particles in a liquid carrier, such as water or a mixture of water and a water miscible organic solvent, that does not dissolve the resin, with heating to a temperature at which the resin particles soften until they become spherical or almost so, followed by cooling of the dispersion and separating and drying the toner particles.

Dispersion-heat process employing hydrophobic silica for producing

For reversal development of an electrical potential pattern formed by imagewise exposure of a uniformly charged photoconductive layer, the charging of the layer is restricted to such a level below its breakdown voltage that the contact between the photoconductive layer and the toner powder used in the development step is insulating, and a magnetisable and inductively attractable toner powder is applied for the development. The toner powder is applied by means of a magnetic brush device comprising a conductive development roller which is provided with an electrical potential suited for reversal development. Preferably the photoconductive layer is charged to a level of at most 35-75% of its breakdown voltage, and a scorotron preferably is used for the charging. The photoconductive layer may comprise a photoconductive polymer and/or a bisazo pigment as photosensitive compound, or may be a layer of 'pink' zinc oxide dispersed in a binder.

Growing community of inventors

Panningen, Netherlands

Roelof R Hendriksma