Electrocoagulation printing method and apparatus providing enhanced image resolution

In 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) forming on said positive electrode active surface a plurality of dots of colored, coagulated colloid representative of a desired image, by electrocoagulation of an electrolytically coagulable colloid present in an electrocoagulation printing ink comprising a liquid colloidal dispersion containing said electrolytically coagulable colloid, a dispersing medium, a soluble electrolyte and a coloring agent;
• c) bringing an endless non-extensible belt moving at substantially the same speed as the positive electrode active surface and having on one side thereof a colloid retaining surface adapted to releasably retain dots of electrocoagulated colloid, into contact with the positive electrode active surface to cause transfer of the dots of colored, coagulated colloid from the positive electrode active surface onto the colloid retaining surface of the belt and to thereby imprint the colloid retaining surface with the image;
• d) repeating steps (b) and (c) 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 thereby produce several differently colored images of coagulated colloid which are transferred at respective transfer positions onto said colloid retaining surface in superimposed relation to provide a polychromic image;
• and
• e) bringing a substrate into contact with the colloid retaining surface of said belt to cause transfer of the polychromic image from said colloid retaining surface onto said substrate and to thereby imprint said substrate with said polychromic image;
• the improvement wherein step (b) is carried out by:
• i) providing a series of negative electrolytically inert electrodes each having a surface covered with a passive oxide film, said negative electrodes being electrically insulated from one another and arranged in rectilinear alignment so that the surfaces thereof define a plurality of corresponding negative electrode active surfaces disposed in a plane spaced from said positive electrode active surface by a constant predetermined gap, said negative electrodes being spaced from one another by a distance smaller than said electrode gap;
• ii) coating said positive electrode active surface with an olefinic substance to form on the surface micro-droplets of olefinic substance;
• iii) filling the electrode gap with said electrocoagulation printing ink;
• iv) 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;
• v) 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 said dots of colored, coagulated colloid;
• and
• vi) removing any remaining non-coagulated colloid from said positive electrode active surface.

In an electrocoagulation printing apparatus comprising:

• a positive electrolytically inert electrode having a continuous passivated surface defining a positive electrode active surface;
• means for moving said positive electrode active surface at a substantially constant speed along a predetermined path;
• means for forming on said positive electrode active surface a plurality of dots of colored, coagulated colloid representative of a desired image, by electrocoagulation of an electrolytically coagulable colloid present in an electrocoagulation printing ink comprising a liquid colloidal dispersion containing said electrolytically coagulable colloid, a dispersing medium, a soluble electrolyte and a coloring agent;
• and
• means for bringing a substrate into contact with the dots of colored, coagulated colloid to cause transfer of the colored, coagulated colloid from the positive electrode active surface onto said substrate and thereby imprint said substrate with said image;
• the improvement wherein said means for forming said dots of colored, coagulated colloid comprise:
• a series of negative electrolytically inert electrodes each having a surface covered with a passive oxide film, said negative electrodes being electrically insulated from one another and arranged in rectilinear alignment so that the surfaces thereof define a plurality of corresponding negative electrode active surfaces disposed in a plane spaced from said positive electrode active surface by a constant predetermined gap, said negative electrodes being spaced from one another by a distance smaller than said electrode gap;
• means for coating said positive electrode active surface with an olefinic substance to form on the surface micro-droplets of olefinic substance;
• means for filling the electrode gap with said electrocoagulation printing ink;
• means for applying to said negative electrodes a pulsed bias voltage ranging from −1.5 to −40 volts and having a pulse duration of 15 nanoseconds to 6 microseconds, so that the bias voltage applied is inversely and non-linearly proportional to the pulse duration;
• means for 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 said dots of colored, coagulated colloid;
• and
• means for removing any remaining non-coagulated colloid from said positive electrode active surface.

In a multicolor electrocoagulation printing apparatus comprising:

• a positive electrolytically inert electrode having a continuous passivated surface defining a positive electrode active surface;
• means for moving said positive electrode active surface at a substantially constant speed along a predetermined path;
• an endless non-extensible belt having on one side thereof a colloid retaining surface adapted to releasably retain dots of electrocoagulated colloid;
• means for moving said belt at substantially the same speed as said positive electrode active surface;
• a plurality of printing units arranged at predetermined locations along said path, each printing unit comprising:
• means for forming on said positive electrode active surface a plurality of dots of colored, coagulated colloid representative of a desired image, by electrocoagulated of an electrolytically coagulable colloid present in an electrocoagulation printing ink comprising a liquid colloidal dispersion containing said electrolytically coagulable colloid, a dispersion medium, a soluble electrolyte and a coloring agent, and
• means for bringing said belt into contact with said positive electrode active surface at a respective transfer station to cause transfer of the dots of colored, coagulated colloid from the positive electrode active surface onto the colloid retaining surface of said belt and to imprint said colloid retaining surface with the image,
• thereby producing several differently colored images of coagulated colloid which are transferred at said respective transfer stations onto said colloid retaining surface in superimposed relation to provide a polychromic image;
• and
• means for bringing a substrate into contact with the colloid retaining surface of said belt to cause transfer of the polychromic image from said colloid retaining surface onto said substrate and to thereby imprint said substrate with said polychromic image;
• the improvement wherein said means for forming said dots of colored, coagulated colloid comprise:
• a series of negative electrolytically inert electrodes each having a surface covered with a passive oxide film, said negative electrodes being electrically insulated from one another and arranged in rectilinear alignment so that the surfaces thereof define a plurality of corresponding negative electrode active surfaces disposed in a plane spaced from said positive electrode active surface by a constant predetermined gap, said negative electrodes being spaced from one another by a distance smaller than said electrode gap;
• means for coating said positive electrode active surface with an olefinic substance to form on the surface micro-droplets of olefinic substance;
• means for filling the electrode gap with said electrocoagulation printing ink;
• means for applying to said negative electrodes a pulsed bias voltage ranging from −1.5 to −40 volts and having a pulse duration of 15 nanoseconds to 6 microseconds, so that the bias voltage applied is inversely and non-linearly proportional to the pulse duration;
• means for 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 said dots of colored, coagulated colloid;
• and
• means for removing any remaining non-coagulated colloid from said positive electrode active surface.