A Bench Test for Predicting the Effect of the Fountain Solution on Pick and Curl of Offset Papers.

n offset lithography, minute quantities of the aqueous fountain solution are transferred to the paper surface from the rubber printing blanket. Two adverse paper reactions to such wetting are: a. Wet curl; curling of paper sheets on the delivery table due to press moisture transferred to the printed side. b. Wet pick; in multicolor presses, paper pick in the later units due to softening of surface bonds by press moisture from an earlier color unit. To study such paper reactions, a test instrument is described which permits controlled wetting of paper specimens at very low levels of water transfer, using the offset gravure principle. The water transfer level and time delay intervals after wetting are extremely critical regarding the bench test for wet curl and wet pick. Such test parameters have been established by correlation studies of paper performance on commercial offset press equipment. The testing instrument and methods for measuring wet curl and wet pick are described in detail.