Heat sensitive paper, you may feel more strange .In fact, it plays an important role in shopping malls and supermarkets .For example, when you go to the shopping mall, select the goods you need and pay for them, the cashier prints out the receipt for you, which is the same paper. what’s so unique about thermosensitive paper? How is this shopping slip printed?
When we talk about printing, we send ink to a specific area of the paper in a specific way to get the text or graphics we want. The chemicals that make up the paper don’t absorb any color of light, so when light bounces off the surface of the paper into our eyes, we see that the paper is white. The pigments or dyes in the ink absorb some or all of the visible light, so that when the ink is applied to the surface of the paper, the surface becomes colored. The printers that we use at home or in the office are mainly ink-jet printers and laser printers. Ink-jet printers spray tiny droplets of ink onto paper, while laser printers do this by electrostatic attraction, first attaching toner to a light drum and then transferring them to paper.
However, the purchase receipt is not printed in this way, it USES a special kind of paper – thermal paper.
Compared with ordinary paper, thermosensitive paper has a thin layer of coating on the surface, which contains some special chemicals called cryptochrome dyes. The dye itself is colorless, so newly bought thermal paper looks as white as regular paper. However, when the right conditions are met, they react chemically, and the newly created material can absorb visible light, and we see color. For example, many substances, such as crystalline violet, although colorless by themselves, turn purple once they encounter acidic substances, and turn colorless again when they encounter alkaline substances. That is, when we print on thermosensitive paper, the ink is not stored in the printer, but already on the paper