Planographic printing plate

Claim 1

A PRESENSITIZED, DIMENSIONALLY STABLE PLATE SUITABLE FOR LITHOGRAPHIC PRINTING AND RELATED USE, AND CAPABLE OF BEING SHIPPED IN LIGHT-PROOF PACKAGES, STORED AND THEN USED WEEKS OR MONTHS AFTER MANUFACTURE, COMPRISING AN ALUMINUM SHEET HAVING ON AT LEAST ONE SURFACE THEREOF A PERMANENTLY HYROPHILIC SCUM-PREVENTING AND TONE-REDUCING FILM FORMED BY REACTING AN AQUEOUS SOLUTION OF A SOLUBLE SILICATE WITH THE SURFACE OF SAID ALUMINUM SHEET, SAID FILM OVERLYING AND BEING FIRMLY BONDED TO SAID SURFACE OF SAID SHEET AND BEING SUBSTANTIALLY FREE OF WATER-SOLUBLE MATERIAL, SAID FILM BEING FURTHER CHARACTERIZED IN THAT IT WILL CAUSE AN IN SITU INSOLUBILIZED DIAZO IMAGE STRONGLY TO ADHERE TO THE SURFACE OF THE SHEET, AND OVER AND IN CONTACT WITH SAID FILM A THIN COATING OF A LIGHT-SENSITIVE DIAZO RESIN, SAID LIGHTSENSITIVE MATERIAL BEING CHARACTERIZED IN THAT, UPON EXPOSURE OF THE PLATE TO ULTRA-VIOLET LIGHT THROUGH A STENCIL OR NEGATIVE, IT WILL REACT IN THE EXPOSURE PORTIONS EXPELLING NITROGEN FROM THE MOLECULE AND FORMING A WATER-INSOLUBLE HYDROPHOBIC AND ORGANOPHILIC MATERIAL WHICH IS TIGHTLY BONDED TO SAID PERMANENTLY HYDROPHILIC FILM, PROVIDING A PRINTING IMAGE, THE LIGHT-SENSITIVE RESIN MATERIAL BEING READILY WASHED AWAY FROM THE UNEXPOSED AREAS, LEAVING THE PERMANENTLY HYDRROPHILIC FILM BARE IN SAID AREAS, SAID HYDROPHILIC FILM BEING FURTHER CHARACTERIZED IN THAT IT WILL PREVENT THE METAL FROM CAUSING DECOMPOSITION OF THE DIAZO LIGHT-SENSITIVE MATERIAL, THUS PROVIDING LONG SHELF LIFE FOR THE PRESENSITIZED PLATE.