Thermal printers work on the principle of the transfer of heat to print matter onto paper. They do this by selectively heating specially coated paper when the thermal head traverses its surface. The area where the heat is applied to turns black, thus creating an impression of text or an image. Black and red color printing is possible by heating the coated paper at different temperatures.
There are two types of thermal printers - direct thermal and thermal wax transfer printers. Direct thermal printing was once used in fax machines. Dot matrix printers are generally replaced with direct thermal printers because of the advantages they offer such as better speeds and silent operation. Because thermal printers can only print in black and one other color they are generally used to print receipts and other types of general documents. These printers can create pretty good images however they aren’t as sharp as laser-printers.
All you really need to operate thermal printers are the rolls of thermo-sensitive paper. This is a great advantage as there is no ink or ink cartridges that have to be replaced. The thermal wax transfer printer uses a wax-based ink that is designed to melt images onto the paper. This type of thermal printer doesn’t use thermo-sensitive paper however it does need to have its ink replaced when it runs out. This type of printer is a bit faster than a direct thermal printer.
Thermal printers are prone to certain disadvantages however such as abrasion and friction, which may deteriorate the quality of the print. The paper's sensitivity to heat and the fragile nature of the paper coating must also be observed to ensure proper quality of print. Excessive heat may darken the paper too much, light could fade the colors and water can spoil the print completely - these are some of the things to be considered when handling thermal printers.