Physiology and Function of Thermal Printers
Thermal printers have never been more popular than they are today. They are used in a variety of industries, from hospitals to cash registers that print receipts in retail stores and restaurants. Thermal printers have become especially important in biomedical research because they are resistant to many of the harsh environments encountered in laboratories. So how do these printers work?
Thermal Printers vs Digital Printers
Digital printers (inkjet and laser) rely on inks applied to labels. Inkjet printers eject ink through nozzles, while laser printers use electrostatic interaction to create an image with toner, which is applied to the surface of the label and then fused to the facestock. In contrast, thermal printers rely on heat to generate images and provide printouts. However, there are two forms of thermal printers, each with their own unique method of printing output: thermal transfer and thermal.
Thermal transfer printer
Thermal transfer printing relies on the printhead heating directly to the ribbon to print output on the label. Ribbons can be made from wax, resin, or a combination of the two, each with different advantages and disadvantages. Pure Resin Ribbons offer maximum resistance to chemical exposure and extreme temperatures, and will not smudge or fade even when exposed to harsh solvents, refrigeration or autoclaving, delivering exceptional print quality. Wax and wax resin ribbons are less resistant to these laboratory environments, making them more suitable for printing paper and general purpose labels for regulatory purposes.
All thermal transfer ribbons consist of a ribbon backing coated with wax, resin or wax-resin blends. When a label is printed, the heated pins of the print head heat and cool according to a pattern instructed by the microprocessor and guided by signals from the labeling software. The needles of the heated printhead then heat the ribbon's wax or resin, which melts and transfers from the ribbon's backing to the label. The used portion of the ribbon is then wound around the ribbon take-up shaft until the entire ribbon is used. Typically, the ribbon sensor notifies the system when the roll is completely empty, protecting the printhead from damage. There is also an end core sensor in the ribbon unwind, which senses when the ribbon stops unwinding by detecting the end of the ribbon that separates from the core.
thermal printer
Direct thermal also uses heat to generate printouts, but instead of using ribbon as a source of ink-like material, the entire label is coated with leuco dye, a chemical that changes color when heated. The printer's "thermal head" generates heat directly on the label with the help of a "spring" that applies pressure to the thermal head as the roller feeds the label.
