Details:
Summary:
In part I, we described the mechanism that led to print defects caused by plastic contaminants in both newsprint and value-added mechanical sheets. We found that these defects were created in the same way that conventional hickeys are, but that they showed very specific characteristics when viewed under a microscope. The source of contaminant was identified and the situation corrected.
In this study, we report outbreaks of print defects that have appeared in a large pressroom on newsprint and were first thought to be caused by plastic contamination; hence the paper was singled out as the source of the problem. The defects appeared as "white spots" on both solid images and high coverage screens and after a preliminary investigation in microscopy, it seemed again that the mechanism of formation was akin to classical hickeys.
The defects presented here constitute another breed of hickeys that is not random as they create stationary defects in the printed images. They showed to be resistant to the conventional methods of removing contaminants on an offset press. They have proven to be disastrous to print quality.
The hickeys were caused by iron particles adhering to the printing plates. Through various extensive microscopy analyses it was established that the ink was the source of contamination and not the paper.