Vanishing ink could bolster recycling.

An erasable printer ink could offer a better way to reuse and recycle office paper, say scientists at Toshiba Corp.'s Research and Development Center in Kawasaki, Japan. Erasing a printed document would allow workers to use a piece of paper several times before sending it to a central plant for recycling.

The prototype ink developed by Shigeru Machida and his colleagues contains three components: a dye, a developer, and an erasing agent. When the dye is bound to the developer, it looks black. Dripping a solvent over the ink, however, breaks the bond, turning the dye invisible. A new bond then forms between the developer and the erasing agent. That way, "the color never returns," Machida notes.

The researchers have demonstrated the process by running a pen containing the solvent over a document. So far, they've printed and erased each document as many as 10 times. Machida says, "The printing quality doesn't change, but the paper eventually gets mechanically damaged." Then, dog-eared paper could be hauled to a recycling plant, where heat treatment would make the ink colorless. This could result in whiter recycled paper.

Currently, recycled paper made from office waste often appears yellowish because the ink can't be completely removed. Repeating the conventional ink-removal process does result in whiter paper but requires large amounts of electricity and water.