Thermal paper, also known as thermal recording paper, thermal copy paper, and thermal fax paper, was first developed by Minesota Mining Ink Character in 1951.

Two-component thermal paper with colorless dyes is a kind of processing paper coated with special coatings. It is a kind of information paper which uses paper as the carrier, recessive colorless dyes, developers, sensitizers, adhesives, etc. as thermal chromogenic coatings.

The evaluation of thermal paper quality includes the following aspects:

(1)The smoothness of the thermal paper

The smoothness of thermal paper has a direct impact on the brightness and color sensitivity of pictures and texts. The higher the smoothness, the higher the chromogenic density and the stronger the adaptability. This is because the smoother the surface of the paper, the closer the thermal printing head of the fax machine can be to the coating layer of the paper, the more effective the heat of the thermal printing head can be transferred to the sensible heat surface, which speeds up the melting speed of the medicine, the rapid color reaction and the speed of transferring pictures and texts. The smoothness of thermal paper is generally higher than 300 s.

(2)thermal paper chromogenic performance

Different thermal papers have different standards and requirements according to their uses, such as color temperature and speed. In addition to meeting the physical indicators of the normal operation of users'machines, the main requirements in graphics are color density > 1.20D and background color < 0.10D.

The chromogenic performance (chromogenic temperature, chromogenic speed) of thermal paper reflects the sensitivity of thermal paper and the clarity of image recording. It is an important index to measure the performance of thermal paper.

(3)the preservation of thermal paper

The preservation (light resistance, heat resistance, and moisture resistance) of thermal paper reflects the image stability of thermal recording paper. They are another important index to measure the performance of thermal paper.

The light resistance of thermal paper means that the printed paper is placed in the fluorescent lamp box, keeping the illumination of 5000lux, and after 100 hours, taking out the value of the test color light density, requiring the image retention rate not less than 85%. Heat resistance of thermal paper means that the printed paper is placed in the oven, and the temperature is kept at 50 C. After 24 hours, the color rendering optical density value is taken out, which requires the image retention rate to be more than 85%.
The humidity resistance of thermal paper means that the printed paper is placed in a constant temperature and humidity box (90% relative humidity, 40 C). After 24 hours, the value of color development density is taken out and the image retention rate is required to be more than 85%.

(4)Homogeneity of thermal paper coatings

The thermal paper requires a uniform coating. If the coating of thermal paper is not uniform, it will lead to dark color in some places, light color in some places, and the quality of printing will be significantly reduced. In addition, the thermally sensitive layer should have a certain fastness, without powder dropping. Otherwise, the dropping coating will stick to the printing head, which will affect the imaging effect and the service life of the machine.