Compared with ordinary paper, hot sale thermal paper roll has a thin coating on its surface, it contains some special chemicals called leuco dyes. The leuco dye itself is colorless, so the new thermal paper looks as white as ordinary paper.  However, it will make chemical reaction once they meet the right conditions, the newly produced material absorbs visible light, so we see the color, such as crystal violet lactone and many other substances, Although it is colorless, it turns purple when it comes to acid. In other words, when we print with thermal paper, the ink is not stored in the printer, but already covered in the paper.

Thermal paper used to print small tickets is usually made into a roll. When a roll of thermal paper is placed in the printer, it will be driven forward by the roller, contacting the print head.  There are many tiny semiconductor elements on the surface of the print head that can be heated to specific areas of the paper according to the text or graphics we want to print. At the moment when the thermal paper came into contact with the print head, the high temperature produced by the printing head causes the dyes on the surface of the thermistor paper to melt together with acidic substances to form a liquid and undergo chemical reactions, so the surface of the paper appears as text or graphics. If driven by the roller, a shopping ticket is printed out.