(57) A printing system incorporates a re-usables image-carrying printing surface. A material
which forms a thin hydrophobic layer is arranged by various techniques over a substantially
hydrophilic printing surface in a configuration which defines the desired latent image
in terms of exposed, contiguous hydrophilic and hydrophobic areas. Depending upon
the configuration of the layers, either an aqueous, or oleo ink may be used to develop
and print an image. If desired, the layer configuration may be replaced by a different
configuration without substantial interruption to the printing process. No photo-induced
chemical reaction or latent image developing steps are required at any time. In a
typical apparatus, the hydrophilic surface of a printing roll (10) is cleaned (12-16)
and coated with a hydrophobic material (20-24), and the hydrophobic material is physically
removed from selected areas: by a computer-addressable spark discharge (26-30), laser
or other device to form a latent image. A fountain liquid is subsequently applied
(40), followed by an ink (50), and the ink image is transferred to a substrate to
be printed either directly (8) with the help of a pressure roll (6) or indirectly
(8A) through an offset roll (6).
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