The Measurement of the Drying of Letterpress and Lithographic Inks on Coated Book Papers.

A working procedure for laboratory measurements of ink drying on paper is demonstrated using the I.G.T. Drying Time Recorder. This instrument gives a continuous time record of ink transferred from a wet paper print to a standard chart. Clear cellulose acetate serves as the record chart, ink set-off being measured in terms of the light transmission of the ink set-off record. The end point of drying is defined as the time after printing where ink transfer to the chart terminates under a standard load of 1725 pounds per square inch. Papers are printed under a standard set of conditions with testing limited to solid prints only. Data are shown for ink drying tests of a survey nature run with regular commercial samples of letterpress coated book papers printed with letterpress halftone black inks, and lithographic coated book papers printed with black lithographic inks. Principal findings are: A. Drying times for a given paper vary over a broad range depending upon the choice of test ink. B. For a given ink, differences between papers cover a narrower range. C. Drying properties of the inks change with aging. D. A close relation does not exist between setting properties and drying times of the inks, in general. E. The printing film thickness has a critical effect on the drying time for ink on paper. F. Drying of the ink on paper is slowed at high relative humidities. G. Raising the drying air temperature reduces the ink drying time on paper.