I have halftone dots that aren't printing but are still visible on the plate on my web press. What could be causing this?
Nov 2, 2020

Although this could be caused by many factors, it sounds like plate blinding. Calcium carbonate is used as a filler and coating ingredient in paper. The calcium can accumulate on the blanket and dissolve into the fountain solution, having a neutralizing effect on pH of the fountain solution on the plate surface. Under certain conditions, the calcium carbonate will accumulate on the image areas on the plate, attracting the gum to which the water molecules will adhere, causing image areas to repel ink. Calcium carbonate is water soluble, so good ink/water balance is critical to minimize the amount of calcium dissolved into the system. During long runs on a web press, using stock that is not properly sized to increase the water resistance can contribute to the likelihood of plate blinding even with good ink/water balance. Using a fountain solution etch formulated to counter the effects of calcium carbonate can reduce or delay the blinding.

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