Green Chemistry Challenge: 2017 Designing Greener Chemicals Award
The Dow Chemical Company
Papierfabrik August Koehler SE
Breakthrough Sustainable Imaging Technology for Thermal Paper
Dow Chemical Company, Collegeville, Pennsylvania, in partnership with Papierfabrik August Koehler SE, Germany, is being recognized for developing a thermal printing paper which eliminates the need for chemicals used to create an image, such as bisphenol A (BPA) or bisphenol S (BPS). Thermal paper is used broadly throughout the world for cash register receipts, tickets, tags, and labels. This technology reduces costs by creating records that do not fade, even under severe sunlight, allowing the original document to be preserved for long term storage. The paper is compatible with thermal printers currently in commercial use around the world.
Summary of Technology:
Thermal paper is widely used for cash register receipts, tickets, tags, and labels. Direct thermal printers form images by heating the paper, which contains a reactive combination of leuco dye and acidic developer. In the presence of heat, the dye is protonated by the developer to create a color change from white to black. Current thermal papers use chemicals such as free bisphenol A (BPA) and bisphenol S (BPS), which are more available for human exposure than bisphenol polymerized into a resin.
The Dow Chemical Company and Koehler jointly developed a patented thermal paper technology that completely eliminates the use of chemical developers (BPA or BPS) and other reactive chemistries. This new thermal printing technology relies solely on the collapse of air voids in the paper coating during printing. Polymer properties are tailored so that a physical change, rather than a chemical reaction, creates the image. It is a commercially viable drop-in alternative for conventional thermal papers, avoids retailer and consumer exposure to imaging chemicals, and does not fade even under severe sunlight. Using this technology, documents such as medical records would not have to be photocopied for long term storage.
The new voided thermal paper is comprised of three layers, including a top opaque layer, a colored layer and a base paper. The colored layer contains only polymeric binders and permanent pigments such as carbon black. The opaque layer contains hollow particles that create air voids in the coating, allowing it to hide the underlying dark colored layer. When heat is applied to the paper from the thermal print head, it causes localized collapse of the hollow particles. The opaque coating then becomes transparent only where the collapse has occurred and the underlying colored layer is visible and creates an image.
The polymer used in the opaque layer, ROPAQUETM NT-2900 Opaque Polymer, is produced in full scale commercial reactors. The paper has been tested at four stores owned by a small food chain in Germany and at a home center in London in 2014. The technology has also received strong interest by larger chain stores. A large-scale commercial roll-out is planned in 2017.