Diazo lithographic printing plate developing process
AssigneeHoward A. Fromson
InventorsRobert F. Gracia, Howard A. Fromson
Life of this patent
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Abstract
Process for removing unexposed diazo from a silicated aluminum lithographic printing plate having a hydrophilic, anionic, negatively charged surface and a layer of a light sensitive, cationic diazo material which has been selectively exposed to actinic light in an image area. The plate is contacted after exposure with a solution of an anionic material in water. Anionic material from the solution ionically couples with unexposed diazo material and the solution still containing anionic material dissolves the coupled product from the unexposed areas producing a clean, hydrophilic background.
Claims6
Process for removing unexposed diazo from a lithographic printing plate comprising a silicated aluminum substrate having a hydrophilic, anionic, negatively charged surface and on and bonded to the substrate, a light sensitive, cationic, positively charged, water-soluble diazo material which has been selectively exposed to actinic light in an image area which comprises contacting the plate after exposure with a solution consisting essentially of an anionic material in water in a quantity and for a time sufficient to couple the diazo with the anionic material and dissolve the coupled product from the non-image area thereby overcoming the bond between the diazo and the substrate leaving a clean, hydrophilic non-image area.
Process for removing unexposed diazo from a lithographic printing plate consisting essentially of providing a silicated aluminum substrate having a hydrophilic, anionic, negatively charged surface and on and bonded to the substrate, a light sensitive coating consisting essentially of a cationic, positively charge, water-soluble diazo material which has been selectively exposed to actinic light in an image area, contacting the plate after exposure with a solution consisting essentially of an anionic material in water in a quantity and for a time sufficient to couple the diazo with the anionic material and dissolve the coupled product from the non-image area thereby overcoming the bond between the diazo and the substrate leaving a clean, hydrophilic non-image area and rinsing with water.
Dependencies are inferred from the claim text.