Proceedings PaperTechnology of direct thermal papers
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Scientists at the NCR Corporation in Dayton, Ohio laboratories invented the basic technology used in direct thermal imaging in the early 1960's. Direct thermal is differentiated from thermal transfer and dye sublimation technologies in that images are generated directly on the substrate which contains the active components. Thermal transfer and dye sublimation are characterized by mass transfer from a substrate sheet containing the image forming components to a receiver sheet that holds the final image. Direct thermal coated paper products became commercially available in 1964. The thermal coating components of these early papers had low heat sensitivities, but were well matched to what today would be described as crude and bulky high temperature thermal printheads. The first product, called Miniprint Bond had utility in military applications. Rapid expansion of direct thermal applications began in the l 970's as thermally sensitive papers found uses in chart recorders, calculators, and printers. Direct thermal product developments in the 1980's were characterized by the introduction of facsimile and barcode label papers. More recent developments target specialty applications such as infrared scannable labels, products with colored backgrounds for point of sale (POS) tags/signage, and application of thermal coatings to synthetic substrates for use in medical chart recorders. From the perspective of customer value, direct thermal imaging technology offers several major benefits. For instance, since they have few moving parts the imaging devices require minimal maintenance. This attribute is important in remote locations such as automated teller machines (ATM's) where frequency of use and minimal hardware service are the norm. Another benefit is that direct thermal products are self-contained; the image forming components are on one substrate eliminating the need for transfer ribbons or receiver sheets. Also, speed of printing is important to users, virtually instantaneous imaging is possible with modem printheads and direct thermal papers. Currently, direct thermal products are thought of in terms of two broad product categories: facsimile and label/tag applications. Driving the evolution of facsimile products is the need for cost reduction and increasing image sensitivity. This results from the development of low energy printheads which have longer life and higher facsimile transmission rates. Another concern in facsimile grades is the archivability of imaged sheets for office file storage since the direct thermal image, made by the formation of a chemical complex, may be reversible under certain conditions. Label products, on the other hand, must withstand image erasure due to exposure to a variety of environmental stresses not found in office environments, they include exposure to oils, blood, alcohol, plasticizers as well as wide swings in temperature and relative humidity. The diverse environments in which they find utility result in direct thermal products of increasing complexity with regard to composition and processing of the thermal coatings, as well as place increasing demands on the coating substrate. As a result of technical developments in the areas of hardware and thermal coating design, along with aggressive market development, the world demand for direct thermal products is currently over 400,000 tons per year. Total market growth rate is expected to be over 7% per year for the next several years (Appleton Papers Inc. estimate). The predominant manufacturers of direct thermal products include Appleton Papers Inc., which acquired the thermal assets of the NCR Company in 1978, New Oji/Kanz.aki, Mitsubishi, Ricoh, Koehler, Stora and Nippon/Jujo.