 determined depending on the kind of the electrolyte.
After the anodic oxidation treatment has been administered, the aluminum surface of may be subjected to a hydrophobic treatment as needed. The alkali metal silicate (for example, an aqueous solution of sodium silicate) methods disclosed in U.S. Pat. No. 2,714,066, 3,181,461, 3,280,734 and 3,902,734 can be used for the hydrophobic treatment applicable in the present invention. In these methods, the support is dipped in an aqueous sodium silicate solution or subjected to an electrolytic treatment. Other methods include the methods in which the aluminum surface is treated with potassium fluorozirconic acid as disclosed in Japanese Patent Application Publication (JP-B) No. 36-22063, and the method in which the aluminum surface is treated with polyvinyl sulfonic acid as disclosed in U.S. Pat. No. 3,276,868, 4,153,461 and 4,689,272.
The planographic printing plate of the present invention thus obtained is preferably recorded by an infrared laser.
The positive-type or negative-type recording layer in the planographic printing plate of the present invention is subjected to developing processing with water or an alkaline developing solution after exposure. Because the heat-insulating intermediate layer or the heat-insulating support, which are the distinctive structures of the present invention, have the feature that they become hydrophilic by the alkaline developing solution, the effect of the present invention is most optimally displayed when an alkaline developing processing is administed.
The developing processing may be performed immediately after exposure, or a heat treatment may be performed between the exposure step and development step. When a heat treatment is administered, it is preferable that the temperature is within a range of 60xc2x0 C. to 150xc2x0 C. and that the heat treatment is conducted for 5 seconds to 5 minutes. Various, conventionally known methods may be employed. Examples thereof include a method in which the recording materials are heated by 