A ticket printed on thermal paper. A heat source near the paper will color the paper.

Thermal paper is paper that is impregnated with a chemical that changes color when exposed to heat. It is used in thermal printers and particularly in cheap, lightweight devices such as adding machines, cash registers, and credit card terminals.

The surface of the paper is impregnated with a solid-state mixture of a dye and a suitable matrix; a combination of a fluoran leuco dye and an octadecylphosphonic acid is an example. When the matrix is heated above its melting point, the dye reacts with the acid, shifts to its colored form, and the changed form is then conserved in metastable state when the matrix solidifies back quickly enough.

Typically the coating will turn black when heated. But coatings that turn blue or red are sometimes used.

Most direct thermal papers require a protective topcoating to:

• reduce fading of the thermal image caused by exposure to UV light, water, oils, grease, lard, fats, plasticizers, and similar causes
• provide improved printhead wear
• reduce or eliminate residue from the thermal coating on the thermal printheads
• provide better anchorage of flexographic printing inks applied to the thermal paper
• focus the heat from the thermal printhead on the active coating.

History

The earliest direct thermal papers were developed by NCR Corporation (using dye chemistry) and 3M (using metallic salts). The NCR technology, although the image would fade rather rapidly compared with the much more expensive, but durable 3M technology, became the market leader over time.

Texas Instruments invented thermal print head in 1965, and the Silent 700, a computer terminal with a thermal printer, was put on market in 1969. The Silent 700 was the first thermal print system that printed on thermal paper.

In the 1970s and early 1980s, Japanese producers (such as Ricoh, Jujo, and Kanzaki) using similar dye-based chemistry formed partnerships with barcode printer manufacturers (such as TEC, Sato, and others) and entered the emerging global bar code industry, primarily in supermarkets. U.S. producers such as Appleton (NCR's licensee), Nashua Corporation, Graphic Controls, and others fought to gain market share. Leading pressure-sensitive label producers such as Avery Dennison became major consumers of direct thermal paper for label applications.

In the late 1980s and early 1990s, thermal transfer, laser printing, electrophotography, and, to a lesser extent, ink jet printing began to take away industrial and warehouse barcode applications due to better durability. Direct thermal made a strong comeback with point of sale receipts (gasoline pumps, cash registers, rental car receipts, etc.).

In 2006, NCR Corporation's Systemedia division introduced two-sided thermal printing technology, called "2ST"[1]

See also

• Thermochromism

External links

• Texas Instruments-Computers & Software and Industrial Controls
• Silent 700 Electronic Data Terminals, 1976(PDF)

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