Introduction to thermal paper

Thermal paper is a kind of special coated paper. Its appearance is similar to that of ordinary white paper. The surface of thermal paper is smooth. It is made of ordinary paper as the paper base and coated with a thermal color layer, which is coated on one side of the surface of ordinary paper. The color layer is composed of adhesive, color developing agent and colorless dye (or leuco dye). It is not separated by microcapsules, and the chemical reaction is in a "latent" state. When the thermal paper meets the hot print head, the color developing agent and colorless dye at the printing place of the print head will react chemically and change color to form graphics and text.

When the thermal paper was placed in the environment above 70 ℃, the thermal coating began to change color. The reason for its discoloration should be discussed from its composition. There are two kinds of thermal sensitive components in the thermal paper coating: one is colorless dye or leuco dye; And the other is a color developing agent. This kind of thermal paper is also known as dual group differentiation thermal recording paper.

Commonly used as colorless dyes are mainly crystalline violet lactone (CVL) of triphenylbenzene phthalide system, fluorane system, colorless benzoyl methylene blue (blmb) or spiropyran system. Commonly used as chromogenic agents are mainly para hydroxybenzoic acid and its esters (phbB, PHB), salicylic acid, 2,4-dihydroxybenzoic acid or aromatic sulfone.

When the thermal paper is heated, the colorless dye reacts with the color developing agent to produce color. Therefore, when the thermal paper is used to receive the signal on the fax machine or directly printed with the thermal printer, the text and text will be displayed. Because there are many kinds of colorless dyes, the handwriting colors are different, such as blue, magenta and black.