The average ERIC of the DIP increased from 300 to 350 after the summer effect struck. We have defined Free Ink TM as the percentage of ink remaining in the DIP that is unattached. Paprican ink scanning has revealed the summer effect is not limited to small ink particles. There are several theories regarding the seasonal variation in deinking performance. Our benchmarking shows Southern mills experience symptoms of summer effect more than do Northern mills.
Heat causes ink to cure faster to a harder finish essentially accelerating the aging effect.
Castro, Daneault and Dorris have documented changes in ink character with heat. A second possible cause is a change in furnish such as more low ash, uncoated, SC grade inserts. These inserts could lower the ash balance and raise the quantity of mechanical pulp. A third cause could be changes to the ink types being used. More color is being used in newspapers which means more vegetable oil based inks.