The working principle of a thermal printer is that a semiconductor heating element is installed on the print head. After the print head is heated and contacts the thermal printing paper, the required pattern can be printed out. Its principle is similar to that of a thermal fax machine. The image is created by applying heat to a chemical reaction in the film. This chemical reaction is carried out at a certain temperature. High temperatures accelerate this chemical reaction. When the temperature is lower than 60°C, it will take quite a long time for the paper to become dark, even up to several years; and when the temperature is 200°C, this reaction will be completed within a few microseconds.
The thermal printer selectively heats the thermal paper at certain positions, thus producing corresponding graphics. Heating is provided by a small electronic heater on the printhead that is in contact with the thermally sensitive material. The heaters arranged in square dots or strips are logically controlled by the printer, and when driven, a graphic corresponding to the heating elements will be generated on the thermal paper. The same logic that controls the heating elements also controls the paper feed, thus enabling graphics to be printed across the entire label or paper.
The most common thermal printer uses a fixed print head with a heated dot matrix. The print head has 320 square dots, each of which is 0.25mm×0.25mm. Using this dot matrix, the printer can place the print on any position in the thermal paper. This technology has been used in paper printers and label printers.
