Method of making bimetallic reliefprinting plates

Claim 1

THE METHOD OF MAKING A RELIEF-PRINTING PRINTING PLATE OF THE TYPE COMPRISING A MAGNESIUM METAL BASE PLATE HAVING A THIN ZINC SKIN ON ITS WORKING FACE AND IN WHICH THE IMAGED PRINTING SURFACES ARE IN RELIEF WITH RESPECT TO NON-PRINTING AREAS, SAID METHOD COMPRISING THE STEPS OF FORMING A RESIST IMAGE ON THE SURFACE OF THE ZINC SKIN; REMOVING PORTIONS OF THE ZINC SKIN FREE FROM RESIST TO UNCOVER THE UNDERLYING MAGNESIUM ON THOSE PORTIONS OF THE PLATE THAT ARE TO COMPRISE THE NON-PRINTING AREAS; THEN SUPPORTING THE IMAGED PLATE IN A SUBSTANTIALLY HORIZONTAL PLANE WITH THE IMAGED SURFACE OF THE PLATE FACING DOWNWARDLY; PROPELLING AN ETCHANT UPWARDLY THROUGH SPRAY-NOZZLE MEANS IN HIGH PRESSURE, FINE CONTINUOUS LIQUID STREAMS AGAINST THE DOWNWARDLY FACING PLATE AND SUBSTANTIALLY COVERING THE WORKING FACE OF THE SAME, SAID ETCHANT COMPRISING A SOLUBLE ALUMINUM SALT AND AN OXIDIZING AGENT HAVING THE PROPERTY OF ETCHING THE EXPOSED MAGNESIUM BASE METAL AND REACTING WITH THE LATTER IN THE FORMATION OF A PRECIPITATE INSOLUBLE IN THE ETCHANT WHICH PRECIPITATE IS DEPOSITED ON THE SURFACE OF THE PLATE, SAID STREAMS HAVING SUFFICIENT IMPACT AGAINST THE FACE OF THE PLATE TO PREVENT ACCUMULATION OF PRECIPITATE ON THE UNIMAGED FLAT SURFACES OF THE PLATE WHILE LEAVING THE PRECIPITATE AS A RESIST ON THE ETCH-PRODUCED SIDE WALLS DELINEATING THE NON-PRINTING AREAS ADJACENT THE IMAGED PRINTING SURFACES; CONTINUING SAID ETCHANT PROPELLING OPERATION, WITHOUT INTERRUPTION TO MANUALLY APPLY RESIST, FOR SUFFICIENT TIME TO ETCH THE PLATE TO PRINTING DEPTH; AND FINALLY CLEANING THE PLATE OF RESIST REMAINING THEREON.

Claim 2

THE METHOD OF MAKING A RELIEF-PRINTING PRINTING PLATE OF THE TYPE COMPRISING A MAGNESIUM METAL BASE PLATE HAVING A THIN ZINC SKIN ON ITS WORKING FACE AND IN WHICH THE IMAGED PRINTING SURFACES ARE IN RELIEF WITH RESPECT TO NON-PRINTING AREAS, SAID METHOD COMPRISING THE STEPS OF FORMING A RESIST IMAGE ON THE SURFACE OF THE ZINC SKIN; REMOVING PORTIONS OF THE ZINC SKIN FREE FROM RESIST TO UNCOVER THE UNDERLYING MAGNESIUM ON THOSE PORTIONS OF THE PLATE THAT ARE TO COMPRISE THE NON-PRINTING AREAS; THEN SUPPORTING THE IMAGED PLATE IN A SUBSTANTIALLY HORIZONTAL PLANE WITH THE IMAGED SURFACE OF THE PLATE FACING DOWNWARDLY; PROPELLING AN ETCHANT UPWARDLY THROUGH SPRAY-NOZZLE MEANS IN HIGH PRESSURE, FINE CONTINUOUS LIQUID STREAMS AGAINST THE DOWNWARDLY FACING PLATE AND SUBSTANTIALLY COVERING THE WORKING FACE OF THE SAME, SAID ETCHANT COMPRISING A SOLUBLE ALUMINUM SALT AND AN OXIDIZING AGENT HAVING THE PROPERTY OF ETCHING THE EXPOSED MAGNESIUM BASE METAL AND REACTING WITH THE LATTER IN THE FORMATION OF A PRECIPITATE INSOLUBLE IN THE ETCHANT WHICH PRECIPITATE IS DEPOSITED ON THE SURFACE OF THE PLATE, SAID STREAMS HAVING SUFFICIENT IMPACT AGAINST THE FACE OF THE PLATE TO PREVENT ACCUMULATION OF PRECIPITATE ON THE UNIMAGED FLAT SURFACES OF THE PLATE WHILE LEAVING THE PRECIPITATE AS A RESIST ON THE ETCH-PRODUCED SIDE WALLS DELINEATING THE NON-PRINTING AREAS ADJACENT THE IMAGED PRINTING SURFACES; CONTINUING SAID ETCHANT PROPELLING OPERATION, WITHOUT INTERRUPTION TO MANUALLY APPLY RESIST, FOR SUFFICIENT TIME TO ETCH THE PLATE TO PRINTING DEPTH; AND FINALLY CLEANING THE PLATE OF RESIST REMAINING THEREON.