Investigation into the Causes for

This paper is based on a case study in which a flexographic folding carton printer has suffered intermittently from the print fault "mottle." The printer has had little success with the normal problem solving techniques based on empirical experimentation. The print fault is difficult to cure due to its apparent random nature. Commercial pressure has made the printer focus on this print production problem. Solutions based on empirical testing failed to identify the causes of the problem. Factorial designed experiments allow for the simultaneous study of the effects that several factors may have on a process. By identifying the key interacting factors provoking the "mottle" phenomenon and establishing if the effect was random, it was thought that production efficiency (yield) could be improved.

A two-level factorial experiment was designed to include all of the key components used in normal production. The results and conclusions from the experiment are reported and highlight the preferred properties for each of the key components used in the experiment, which are able to deliver improved printing performance and consistency.