Patent ID: 7194956

Claim:
An offset printing method, comprising the steps of: preparing a printing plate having a surface converted to hydrophilic due to light energy generated at a first temperature, the surface being converted to hydrophobic due to heat energy generated at a second temperature; making forcibly the whole surface of the printing plate either one of hydrophobic or hydrophilic in nature; forming a region having the other one nature of hydrophobic and hydrophilic on a part of the surface of the printing plate so as to correspond to an image to be printed; supplying ink onto the region having the hydrophobic nature; and transferring the ink onto a printing medium to print the image, wherein the material on the printing plate has photocatalyst function, wherein the whole of the surface of the printing plate is made hydrophilic first by irradiating light having a wavelength activating the photocatalyst function, and then a part of the surface of the printing plate is heated at the second temperature to form a hydrophobic region, and wherein the hydrophobic region forming step is performed in an atmosphere in which an organic compound exists.