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Summary:
This article will briefly review the structure of the lithographic plate as it is manufactured today and how it evolved over the last 60 years. Inventions, especially those which significantly improved lithographic plates, are highlighted. The special emphasis is on how these developments were described in TAGA Proceedings over the sixty year period. Since this TAGA Annual Technical Conference (ATC) is the 60th in its history it is most appropriate to highlight how TAGA ATC's have provided the glimpse of the future in offset lithography throughout its 60 technical conferences. We will not cover the hundreds of articles which dealt with other aspects of offset lithography, e.g. inks, paper, presses, etc. Generically the term image carrier refers to the "printing form" or transfer medium, holding the image defined by the input data (now usually digital, formerly film-based), which accepts the ink and applies it to the output substrate. Image carriers include gravure cylinders, flexographic plates, screens and lithographic plates. Strictly speaking since virtually all lithography is printed offset (that is, the plate transfers the ink to a blanket which then transfers the ink to the substrate) lithographic plates are unique image carriers in not directly contacting the substrate during the printing operation. Also, uniquely most practical lithographic plates are virtually planographic, that is, the image is neither raised above nor recessed below the background or non-image areas, but is (typically within 2 microns) in the same plane.