What we usually call printing is to transfer the 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 do not significantly absorb light of any color, so when light is reflected from the surface of the paper into our eyes, we will see that the paper is white. The pigment or dye in the ink can absorb some or even all colors of visible light, so that when the ink is applied to the surface of the paper, the surface of the white paper will take color. The printers we use at home or in the office are mainly inkjet printers and laser printers. The inkjet printer sprays the tiny droplets of ink onto the paper, while the laser printer adsorbs the toner onto the light drum through electrostatic attraction, and then transfers them to the paper.
At room temperature, thermal paper looks no different from ordinary paper; Once the temperature rises, the leuco dyes and acidic substances melt into liquid one after another, and the freely moving molecules react immediately when they meet, so the color is quickly displayed on the white paper. This is why thermal paper gets its name - only when the temperature is high enough to make the paper change color.
Thermal paper also has a big defect, that is, after the documents printed with it are stored for a period of time, the handwriting on it will gradually fade. The fading is also due to the unique dyes used in thermal paper. As we mentioned earlier, the leuco dye covered on thermal paper is colorless at room temperature. At high temperature, it becomes another color structure due to chemical reaction.
If you are worried that a small amount of bisphenol A will enter the body due to contact with the shopping ticket, the more feasible prevention method is to store it separately as soon as possible after receiving the ticket without too much contact, and wash your hands after contacting the ticket. Of course, replacing paper receipts with electronic receipts may be a healthier and more environmentally friendly way.
