Thermal paper is also known as thermal fax paper, thermal recording paper, thermal copy paper, and in Taiwan it is called thermal copy paper. Thermal paper is a kind of processed paper, and its manufacturing principle is to apply a layer of "thermal paint" (thermal discoloration layer) to high-quality base paper. Although there are more than a dozen chemicals used in this color-changing layer, at least the following compounds are available: colorless dyes, which have a wide variety of dyes and commonly use fluorescent compounds; The color developer accounts for about 20% or less, and the commonly used are bisphenol and parabenic acid; Sensitizers account for about 10% or less, which contains benzenesulfonic acid amide compounds; The filler accounts for about 50% or less, and calcium carbonate (particles) is commonly used; Adhesives account for about 10% or less, such as polyvinyl acetate; Stabilizers, such as dibenzoyl p-phthalate; lubricants, etc. Therefore, the process is difficult and the technical requirements are high.