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Thermal PaperThermal paper is used today in an ever increasing number of applications such as point of sales receipts, admission, transportation and lottery tickets, medical records, baggage tags, postage stamps, fax paper, delivery and food retailing labels, to name but a few. Thermal paper consists of a base paper and a coating comprising a layer of heat-sensitive chemicals known as the Thermal Layer. The thermal layer contains a mixture of three key components - color former, color developer and sensitizer. Upon application of heat energy from a thermal print head, the sensitizer melts bringing together the color former and color developer thus forming an image. Usually there are other separate coatings present on the thermal paper, for example: Pre-Coat – an insulating layer that improves the
thermal sensitivity of the paper
To get the paper to react the Thermal Printer has a special head which heats up the paper in required areas, turning them black. Because of this process, and the technology that thermal paper uses, storing documents printed on thermal paper requires a cool area, where the temperature remains in a constant range, and very low humidity. You may have noticed at some point that when you keep a receipt in your wallet, which was printed on Thermal Paper, the printing either begins to fade, or the rest of the paper begins to darken (depending on the environment it was in). Care should be taken when attempting to photocopy or scan documents printed on thermal paper, as the heat produced from some scanners and copy machines will black out the paper. Thermal papers are also highly sensitive to light, which can greatly speed up image fading. They retain sensitivity to heat after the actual recording process has been completed. Any further exposure to heat can obscure the printed image by causing the surrounding coating to darken. The coating can similarly be darkened by friction if scored or rubbed against other objects. The thermal coating can also react with solvents such as those used in some highlighters and vapors emitted by polyvinyl chloride (PVC) folders, causing damage to the image. Chemical reactions within the chemical coating of thermal papers can also affect documents stored adjacent. Current evidence indicates that, even with optimum storage and handling conditions, images created on thermal papers will last for only five years. To avoid loss of data in such records, photocopies of thermal paper documents should made on permanent or archival copy paper. If, for whatever reason, an original thermal paper needs to be retained, a copy should be made as a backup, in case the original fades. The paper should then be stored in optimum environmental conditions, ie not exceeding 20°C or 50% relative humidity. Extremes of temperature and humidity can cause rapid deterioration of the image. Avoid prolonged exposure to light as this can also speed up the deterioration of the image. For information on Thermal Paper and Thermal Printers, these pages may help: |
