Dot gain is a printing characteristic which has an effect on printing quality, if it is not controlled. It refers to the physical increase in size for a printed dot during the transfer process between the film and the printed sheet. The purpose of this experiment was to determine whether varying squeeze pressure and blanket tension settings significantly affected directional dot gain (slur and doubling), therefore printing quality, using conventional and compressible types of offset lithographic blankets. The experiment was performed on the second unit of a two-color Heidelberg MOZP sheetfed offset lithographic press, bypassing the first unit. Directional dot gain was evaluated by density readings taken from four RIT Experimental Doubling Targets. An analysis of variance (ANOVA) was performed to determine whether statistically significant differences in dot gain values occurred. It was found that squeeze pressure was a significant factor contributing to the magnitude of slur for both types of blankets, while blanket tension was not. The Fisher test determined that each of the squeeze pressure settings (.006 in. and .008 in. for conventional blankets, .006 in. and .012 in. for compressible blankets) contributed the most towards the difference in dot gain values, while the type of blanket and the different settings of squeeze pressure also contributed to dot gain. Visual examination of the press sheets revealed that directional dot gain occurred at the higher squeeze pressure settings for both conventional and compressible blankets. When both squeeze pressure and blanket tension settings increased, larger dot gain values were detected on conventional blankets. As blanket tension settings increased, dot gain decreased in compressible blankets, since the increased tension decreased the squeeze pressure, by thinning out the blanket.This trend was also noticed on the conventional blankets at the low squeeze pressure setting.
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School of Print Media (CIAS)
Voutsas, Alexander M., "The Effects of blanket tension and squeeze pressure on slur and doubling using conventional and compressable blankets in sheetfed offset lithography" (1991). Thesis. Rochester Institute of Technology. Accessed from
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