we all know that thermal paper use after a long time will change color, and the cause of color is the inside of the thermal paper color layer. Let's to reveal the thermal paper discoloration layer in mystery. Thermal paper discoloration layer consists of the following materials.

a colorless dye, colorless dye is usually a lactone ring or heterocyclic structures of organic molecules. The ideal thermal paper discoloration layer colorless dye itself should be colorless or nearly white, stable at room temperature, not by air oxidation, light does not change color, insoluble in water, at the same time with high concentration of color dye chromogenic agent for rapid response. Here introduced three kinds of commonly used thermal paper discoloration layer colorless dye.

1。 Phthalide class this type of thermal paper discoloration layer colorless dye, use one of the earliest is the dye CVL ( PH值, 1) 。 It presents the bright cobalt blue hair color, the advantage is that color reaction fast, deep color, not sublimation. Although it has a color after poor light fastness were weakness, but because of the price cheap and widely used. To improve the performance of the thermal paper material, people will CVL with other substances is used, it has become a research hotspot.

2。 Phenothiazine and command oxazine class these two compounds belong to heterocyclic molecular. Among them, the most used is the class phenothiazine dye benzoyl methylene blue BLMB. Its characteristic is hair color is slow, but once the hair color it's not easy to fade. If mix with CVL BLMB use, use BLMB not easy fade features to make CVL easy faded up, can get better performance of thermal paper. Dye molecules to command oxazine compounds. These two kinds of compounds with chromogenic agent, color dye forms after the amide bond rupture.

3。 Fluorane type fluorane type is the world's thermal paper dyes development the mainstream, most development prospects. It can render such as yellow, orange, red, green, black color, with black fluorane dyes are the most common. If mix fluorane compounds using, it can be a different color. For example, will send green F - F - 4 and red hair 3 mixed use, can obtain the stability of the black.

2, chromogenic agent chromogenic agent is usually plays a role of proton donor, generally for organic solid acid, often use phenolic compounds. Chromogenic agent itself best colorless or nearly white, low melting point, insoluble in water, and can be rapid response and colorless dye. Bisphenol A ( BPA） Is a kind of commonly used chromogenic agent, its disadvantage is that the high melting point ( 156~158℃） , hair colour sensitivity is low, need to cooperate to use sensitizer. Has now developed a low melting point, high sensitivity of chromogenic agent, such as hydroxy benzyl benzoate.

in addition, usually also need to add some additives in thermal paper discoloration layer, to improve the performance of thermal paper. For example, to join the packing in order to improve the opacity of the paper, to improve the contrast of images and color; Join the adhesive coating has good surface strength and printing performance, at the same time between dyes and chromogenic agent in the formation of colloid protective film, make both isolation to prevent premature reaction; Join the sensitizer to reduce the melting agent, thus to achieve the effect of thermal paper coating reaction speed control.