Use of antioxidants to delay the aging of oil-based inks - The technique offers a practical solution to the poor deinkability of offset inks

The poor deinkability of aged inks is generally ascribed to an oxido-polyme rization of the vegetable oils and/or alkyd resins in some inks used in she et-fed offset and into newspaper inks applied on uncoated papers. The effec tiveness of antioxidants to slow down the oxidative aging of inks and their constituents was determined using a thermogravimetric technique. Previous work using a similar technique had shown that oxidation and polymerization of the ink film was preceded by an induction period whose length decreased exponentially with an increase in temperature. Addition of an antioxidant w as found here to increase substantially the induction period for oil-based vehicles and inks. Of the antioxidants tested, butyl hydroxyanisol (BHA) wa s found to be the most effective. At a dosage of only 0.05% in the ink, the induction time was almost doubled. Hence incorporation of an antioxidant s uch as BHA in news ink formulations represents a practical solution to the problem of poor deinkability of offset inks.