Method of producing an aluminum support for a planographic plate

A method of producing an aluminum support for a planographic printing plate which comprises,

• (1) etching a surface of an aluminum plate chemically in an acidic or alkaline aqueous solution;
• (2) roughening the surface of the aluminum plate electrochemically in an acidic aqueous solution by applying DC voltage, which comprises
• (a) providing at a first roughening stage, a soft starting zone by roughening the aluminum plate at a current density of 100 A/dm.sup.2 or less, which is lower than the current density used in any subsequent main roughening step, for a period of 0.0001 to 5 seconds, and
• (b) carrying out a main roughening step,
• wherein the DC voltage for the roughening is provided by at least one electrode in the soft starting zone connected to a first electric power supply for electrolysis at 100 A/dm.sup.2 or less, and by at least one additional electrode connected to a separate main electric source for electrolysis in said main roughening step,
• the roughening forming honeycomb pits having an average diameter from 0.5 to 7 .mu.m with a density from 40,000 to 500,000 pits/mm.sup.2 and leaving plateau portions without honeycomb pits or with honeycomb pits having an average diameter of less than 0.5 .mu.m at a rate from 0 to 15% of the surface;
• (3) if the plateau portions are 10% or more of the surface, etching the surface of the aluminum plate chemically in an acidic or alkaline aqueous solution to render the plateau portions less than 10% of the surface;
• and
• (4) anodizing or anodizing and rendering hydrophilic the surface of the aluminum plate in an acidic aqueous solution.