Method of etching photoengraving plates and etching solution used therefor

Claim 1

AN ETCH SOLUTION FOR TE ETCHING OF PHOTOENGRAVED PLATES COMPRISING AN AQUEOUS SOLUTION CONTAINING FROM 5 TO 50% OF A WATER-SOLUBLE PERSULFATE AND FROM 1 TO 20% OF A WATER-SOLUBLE CHLORIDE FROM THE GROUP CONSISTING OF AMMONIUM CHLORIDE AND THE ALKALI METAL CHLORIDES.

Claim 3

THE METHOD OF ETCHING A COPPER PHOTOENGRAVING WHILE MAINTAINING THE ETCH RATE AT A HIGH LEVEL WHICH COMPRISES INITIALLY ETCHING THE PLATE WITH A SOLUTION OF AN AQUEOUS PERSULFATE CONTAINING 5 TO 50% OF A WATER-SOLUBLE PERSULFATE AND ALSO CONTAINING FROM 1 TO 10% OF A WATERSOLUBLE CHLORIDE FROM THE GROUP CONSISTING OF AMMONIUM CHLORIDE AND THE ALKALI METAL CHLORIDES, AND, AS THE ETCH RATE GOES DOWN AS THE COPPER CONTENT OF THE ETCH SOLUTION GOES UP, ADDING FURTHER OF SAID WATER-SOLUBLE CHLORIDE IN INCREMENTS TO MAINTAIN THE ETCH RATE.

Claim 4

THE METHOD OF ETCHING A COPPER PHOTOENGRAVING WHILE MAINTAINING THE ETCH RATE AT A HIGH LEVEL WHICH COMPRISES INITIALLY ETCHING THE PLATE WITH A SOLUTION OF AN AQUEOUS PERSULFATE CONTAINING 5 TO 50% OF A WATER-SOLUBLE PERSULFATE AND ALSO CONTAINING FROM 1 TO 10% OF A WATERSOLUBLE CHLORIDE FROM THE GROUP CONSISTING OF AMMONIUM CHLORIDE AND THE ALKALI METAL CHLORIDES, AND, AS THE ETCH RATE GOES DOWN AS THE COPPER CONTENT OF THE ETCH SOLUTION GOES UP, ADDING FURTHER OF SAID WATER-SOLUBLE CHLORIDE IN INCREMENTS TO MAINTAIN THE ETCH RATE.