First of all, we have to understand what is thermal paper. Thermal paper is also known as thermal fax paper, thermal recording paper, thermal copy paper. Thermal paper as a processing paper, its manufacturing principle is in the quality of the base paper coated with a layer of "thermal coating" (thermal color-changing layer). Although there are more than a dozen kinds of chemicals used in the color-changing layer, there are at least the following compounds: colorless dyes, which have many varieties, the most commonly used for fluorescent compounds; Chromogenic agents account for less than 20%, commonly used are bisphenol, hydroxybenzoic acid; Sensitizers accounted for less than 10%, which contained benzene sulfonamide compounds; The filler accounts for about 50% of the following, commonly used calcium carbonate (particles); Adhesives account for less than 10%, such as polyvinyl acetate; Stabilizers, such as dibenzoyl phthalate; Lubricants, etc.
After understanding what thermal paper is, then we'll talk about why thermal paper fades.
The unstable writing generated by fax or printing on thermal paper will fade naturally, the reason is that the color reaction of thermal paper is reversible, the colored product will decompose by itself to different degrees, and the color of the writing will slowly fade more and more shallow, until the natural fade to the white paper completely disappeared.
Therefore, long placement time, long light time, long heating time and at a higher ambient temperature, humid environment, contact adhesive paper and other external conditions under the combined action, will accelerate the decomposition of color products, make its fading speed up. Of course, the fading speed is also related to the heat sensitive layer of the thermal paper itself. (The quality of thermal paper will also determine its fading speed).
There are several points to identify the quality of thermal paper
1: the quality can be seen through the appearance. If the paper is very white, that paper protective coating and thermal coating is not reasonable, add too much phosphor, better should be slightly green. Uneven paper finish, indicating that the paper coating is not uniform, if the paper reflected light is too strong, it is too much phosphor, not very good.
2: fire baking: this method is very simple, is to use a lighter to heat the back of the thermal paper, after heating, the color is brown, indicating that the thermal formula is not reasonable, the preservation time is short. If there are small streaks or uneven patches in the black after heating, the coating is not well distributed. After heating, the color is black and green, and the distribution of color blocks is relatively uniform, and the color becomes light from the center to the surrounding.
3: Sunlight exposure: the printed paper is smeated with a highlighter and exposed to the sun (in order to speed up the reaction time of the heat-sensitive coating), which will turn black the fastest, indicating the shortest storage time. The quality is the worst.
At present, bar code printers are generally printed in two ways. One is our thermal printing, the printed bar code label, generally, the preservation time is relatively short, easy to fade in high temperature environment. But the benefit of thermal printing is that it does not need carbon tape, easy to install, easy to print, no wrinkles, etc.
There is also a heat transfer printing method, also known as carbon tape printing. Its advantage is that the printed content can be stored for a long time, and it can also be resistant to high temperature and low temperature environments.
Post time: Jul-22-2022