Electrocoagulation printing method and apparatus providing color juxtaposition

A multicolor electrocoagulation printing method comprising the steps of:

• a) providing a positive electrolytically inert electrode having a continuous passivated surface moving at substantially constant speed along a predetermined path, said passivated surface defining a positive electrode active surface;
• b) coating said positive electrode active surface with an olefinic substance to form on the surface micro-droplets of olefinic substance;
• c) forming on the olefin-coated positive electrode active surface a plurality of colored pixels representative of a desired polychromic image, each pixel comprising juxtaposed dots of differently colored, coagulated colloid, step (c) being carried out by:
• i) providing a series of negative electrolytically inert electrodes each having a cylindrical configuration with a predetermined cross-sectional dimension and an end surface covered with a passive oxide film, the negative electrodes being electrically insulated from one another and arranged in rectilinear alignment so that the end surfaces thereof define a plurality of corresponding negative electrode active surfaces disposed in a plane spaced from the positive electrode active surface by a constant predetermined gap, said negative electrodes being spaced from one another by a distance smaller than the electrode gap;
• ii) filling the electrode gap with an eletrocoagulation printing ink comprising a liquid colloidal dispersion containing an electrolytically coagulated colloid, a dispersing medium, a soluble electrolyte and a coloring agent;
• iii) applying to the negative electrodes a pulsed bias voltage ranging from −1.5 to −40 volts and having a pulse duration of 15 nanoseconds to 6 microseconds, the bias voltage applied being inversely and non-linearly proportional to the pulse duration;
• iv) applying to selected ones of said negative electrodes a trigger voltage sufficient to energize same and cause point-by-point selective coagulation and adherence of the colloid onto the olefin-coated positive electrode active surface opposite the electrode active surfaces of said energized electrodes while said positive electrode active surface is moving, thereby forming dots of colored, coagulated colloid;
• v) removing any remaining non-coagulated colloid from said positive electrode active surface;
• and
• vi) repeating steps (i) through (v) several times to define a corresponding number of printing stages arranged at predetermined locations along said path and each using a coloring agent of different color to produce dots of differently colored, coagulated colloid, the distance between the negative electrodes of each printing stage being at least three times the cross-sectional dimension of each negative electrode to permit juxtaposition of said dots of differently colored, coagulated colloid, thereby forming said colored pixels;
• and
• d) bringing a substrate into contact with the colored pixels to cause transfer of said colored pixels from the positive electrode active surface onto said substrate and thereby imprint said substrate with said polychromic image.