Thermal paper is coated with a mixture of chemicals that react when exposed to heat to create an image. The exact composition of the coating can vary depending on the manufacturer and intended application, but typically includes the following chemicals:
Colorless dyes: These are often used in combination with a developer chemical that reacts with heat to produce a visible color. Examples include leuco dyes such as crystal violet lactone, triarylmethane, fluoran, and spiropyran.
Developer chemicals: These are typically acidic compounds that react with the colorless dyes when heated to produce a visible color. Common examples include bisphenol A and phenol sulfonates.
Sensitizers: These chemicals are used to improve the sensitivity of the thermal paper and enhance the color produced by the developer and dye mixture. Examples include aromatic amines and guanidine compounds.
Stabilizers: These chemicals are used to prevent the coating from degrading over time or when exposed to heat, light, or moisture. Examples include phenolic antioxidants and UV absorbers.
Overall, the coating on thermal paper is a complex mixture of chemicals that work together to produce a clear and legible image when exposed to heat.
