Details:
Summary:
There were three objectives of this study. We wanted to compare the printability of different blankets with all other conditions equal. For a constant paper and press, we wanted to look for differences in interstation press movement of marks that could be attributed to blanket properties. Finally, this was an opportunity to compare process variability due to blankets and contrast this variability with a parallel project dealing with printing plates. The first and last objectives were achieved while the second objective dealing with movement is more complicated. The movement question created more questions than answers, but it can be assumed that the sheet or blanket movement aspect presents the greatest opportunity to learn more about blanket and press dynamics. Seven companies agreed to participate, as long as the results were coded. Some blanket companies provided two blankets, and the total is 12 blankets. Before printing, the blankets were carefully measured for smoothness, caliper, and high magnification digital photographs were collected of the surface. The blanket suppliers were polled as to what tension to torque and what blanket to plate squeeze to use. The various answers will be shared as well as the final settings chosen for the study. All blankets received identical treatment. Printing may have been on a different day, but the press, paper, ink, fountain chemistry, speed, plate, and temperature were identical. Random samples were pulled for print attribute measurement, and 30 consecutive sheets were measured with the Mitsubishi Digital Register Analysis System. All the blankets were printed to the same approximate solid ink densities. The resulting tone value increases (dot gains) were remarkably close, exhibiting a range of perhaps 5% over all 12 blankets. The movement measurements showed much equivalence between all the blankets, for units 1-2 and 2-3. On the transfer between units 3-4, there were some differences between the 12 blankets. Some of the blankets showed twice the movement as others, but only on the one cylinder couple. This phenomenon will be the subject of further study and discussion with the press manufacturer. The printed samples were examined in the solids for ink lay and in the quarter tones for dot structure. It was clear from photomicrographs that some blankets, under these conditions, print better solids while others print sharper dots.