ELEKTROGRAFISKT FRAMKALLNINGSFOERFARANDE

1412350 Electrographic development MINNESOTA MINING & Mfg CO 14 March 1973 [15 March 1972] 12281/73 Heading G2H A latent electrostatic image on a surface of a layer 3 of a recording element is developed with a toner material (13) which is both electronically conductive and magnetically attractable, the toner material (13) being applied by an electrically conductive support, e.g. a shell 11 of a development roller 8, to which it is held by magnetic attraction and which is at a direct current electrical potential of a magnitude and polarity such that the difference in electrical potential between support 11 and said surface results in a transient electrical transfer force on the toner material (13) greater than and opposed to the magnetic force of attraction in image areas and less than the magnetic force of attraction in non-image areas. Chain like groups 17 of the toner material (13), formed by the influence of the magnetic field, provide an electronically conductive path between the shell 11 and the said surface which path is maintained for a period sufficient to allow the transient transfer force to be produced and is then discontinued while the transfer force exists to selectively deposit the toner material (13) on the image areas of the said surface. The layer 3, which may be photoconductive or otherwise, is backed by a conductive layer 4. Both the layer 4 and the shell 11 are earthed.