Thermopapier

Thermopapier, or thermal paper, is a type of coated paper that changes color when heated, enabling direct thermal printing. It is widely used for receipts, tickets, labels and other short-term printouts because no ink or toner is required. The printing image is produced by a heat-sensitive chemical coating on the paper surface.

In the coatings, a leuco dye is combined with a developer and binder. Upon application of heat from a thermal printer, the coating undergoes a chemical reaction that produces a visible image. Direct thermal paper uses the color-forming chemistry on the paper itself. A related technology, thermal transfer printing, uses a heat-sensitive ribbon to transfer pigment to the paper.

Common advantages include fast, quiet printing and simplicity. Limitations include fading of the image over time due to heat, light, and chemical exposure; sensitivity to friction and oils; and the need to store papers away from high temperatures and sunlight.

Safety and environmental aspects center on the chemical developers used in the coating. Many older papers used bisphenol A (BPA) or related compounds; due to health and environmental concerns, many manufacturers now offer BPA-free thermal papers, and some jurisdictions regulate BPA content in consumer receipts. Disposal and recycling of thermal paper can be challenging; coatings and additives can complicate recycling processes.