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Friday, 5 August 2011

The latest Chemical and Engineering News reports on an unforeseen consequence of increased digital printing: getting new kinds of ink off paper in the recycling process. Amanda Yarnell’s article “Rethinking Deinking” provides the details, and here’s my précis.

Paper recycling has been designed around oily inks that float to the surface of a recycling tank and can be skimmed off. Toner in a typical black-and-white laser printer, photocopier, or digital book printer works much the same way. Wikipedia says this process is called “froth flotation.”

However, two newer types of inks cause different sorts of problems. Hewlett-Packard’s Indigo color presses use a liquid toner that can leave colored specks in the new paper. And “high-end ink-jet presses” use ink that’s soluble in water; it doesn’t float up to be skimmed away, but sticks around and makes the new paper a little bit grayer. There’s no way to identify paper that’s been printed with those inks and separate it from the rest.

The article goes on to discuss different ways chemical engineers are working on the problem. Does it require changing the inks? The paper? Or the whole deinking process?

(You remember when recycled paper was first fashionable, and manufacturers made sure it had visible little flecks so we could feel good about using it?)

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