When thermal printer paper is put at environment with above 70℃, thermal coating will change its color, the reason for this should be talked from its ingredients.

There are two kinds of ingredients of thermal coating: one is leuco dye, the other is color developing agent. This kind of thermal printer paper is also called bi-component chemical thermal recording paper. There are some ingredients that are regarded as leuco dye: CVL, fluorane system, BlMB and spirapyran system.

The frequently-used dispersing agent is: polyvinyl alcohol L-3266, polyvinyl alcohol GL-05,  polyvinyl alcohol KL-03 (Japanese synthetic chemical production ). The frequently-used top coating and bottom coating agent is : gohsefimer Z-200, polyvinyl alcohol T-350 and polyvinyl alcohol N-300. The frequently-used color developing agent is : PHBB、PHB, salicylic acid, 2,4 dihydroxybenzoic acid or aromatic sulfone. After getting heat, leuco dye and color developing agent of thermal printer paper will produce chemical reaction, so using thermal printer paper to receive signal or print on the fax machine, words and pictures will be shown. There are many different colors of words like blue, fuchsia and black because of different kinds of leuco dye.