Details of the breakthrough ink and its decoloring process will be presented at the 47^th Polymer Symposium, to be held in Nagoya, Japan, from September 30 to October 2.

Paper disposal is a pressing environmental issue. In Japan, paper accounts for as much as 40 percent of office waste, and although many organizations now collect paper for recycling, the cost and other factors limit the recycling rate to 54 percent. With landfills fast reaching capacity, development of a highly efficient paper-recycling system is attracting increasing concern.

Most paper-recycling systems require large-scale facilities and a complex process. Printed paper is pulped and the ink chemically removed. The pulp is then bleached and delivered to the remaking process. The process is arduous and difficult: successfully removing carbon black, ink's main ingredient and an elemental substance that cannot be broken down or chemically decolored, itself adds to quality degradation and limits recycling volumes.

Toshiba has found a solution with an innovative ink that contains no carbon which decolors completely when exposed to a high level of heat or to solvents. The ink will support a simpler, faster, cheaper recycling process with smaller, more efficient equipment. The new ink will achieve higher recycling yields, and an end product that will be both cheaper and of higher quality than with conventional inks and recycling.

Basic Principal of Decoloration

Toshiba's decolorable ink reverses the reaction that occurs in the development process during printing on thermal paper. Thermal paper is coated with leuco dye and capsulized phenolic developer. Application of heat or pressure breaks the capsule and the dye and developer bond together to form printed images.

Toshiba's new ink contains both the developer and the dye, and a decoloring reagent. The chemical bonding of the dye and developer breaks down at temperatures over 120, or when exposed to certain organic solvents. The detached developer then bonds with the decolorant agent. The printing is erased as the dye and developer separate, and bonding of the developer and decolorant stabilizes the decoloring.

The choice of heat or solvent for decoloring process produces different results. Heat processing is an economic option, which decolors faster with smaller equipment. While the process leaves a residue, the plastic that coats the fixed ink on documents, it produces paper suitable for reuse in-house. Solvent processing erases the plastic coating as well as the ink and achieves complete decoloring of printed letters or images, but is more time consuming and expensive.

Toshiba will promote diffusion of both decoloring systems, in order to meet different needs. The company expects to see development of a market for heat treatment equipment, small enough for installation at business premises. A company with such equipment will be able to reuse its own paper in-house.

Toshiba hopes to work in technical cooperation with other companies to diffuse the new technology worldwide. The company's goal is to promote even higher levels of recycling and to contribute to solving environmental problems.