The amount of missing dots can be measured in a number of ways, there is for instance computer software that together with a flatbed scanner can help you quantify the number of missing dots in your printed product. How big a problem you have with missing dots can be measured according to two variables:
- The number of missing dots per 100 mm²
- Percentage of missing dots in relation to a perfect print
Missing dots are most common in gravure printing and the causes vary. Sometimes the problems are related to the paper topography, such as the paper surface being too coarse, inadequate contact between substrate surface and ink cylinder, or an electrostatic charge that causes the cells in the engraved printing cylinder to not empty properly. Other times it can be caused by uneven fibre and filler distribution or insufficient ink absorbency. There are also factors that can cause missing dots that are not directly related to the paper, such as the use of a printing press or ink that is not optimised for the task at hand.
After doing a thorough analysis of the occurrence of missing dots in your print runs, you will have a good starting point for predicting when and where you might run into problems with missing dots.
Now that you have narrowed down the situations where you most often run into missing dots, it is time for action. Depending on the causes you have found in your analysis, some of the things you can do to improve the situation include cleaning of the ink head, installing electrostatic printing assistance (ESA), or reducing the screen width/resolution.