Thermal paper, essential in various industries including logistics, lottery, medical, and ticketing, serves as a reliable medium for recording information. Differentiated by usage, thermal paper is categorized into two types: thermal paper without a protective layer and thermal paper fortified with one. The former, commonly found in restaurants and cash registers, lacks sufficient protection against scratches, color fading caused by ethanol, oil, or water. In contrast, thermal paper with a protective layer offers superior resistance to scratches and is highly effective in repelling water, oil, and ethanol. This variant is extensively utilized in industries such as welfare lottery, logistics labeling, ticketing, and more.

China's national standards mandate a color retention rate of ≥60% for thermal paper when subjected to ethanol with a volume concentration of 25% for three hours under standard temperature and pressure conditions, using the liquid trap method. Currently, thermal paper available in the Chinese market typically exhibits an ethanol-resistant retention rate of approximately 60%±10%. However, exposure to higher ethanol concentrations, elevated environmental temperatures during detection, or prolonged contact with ethanol can significantly diminish the retention rate, leading to the fading of printed information.

Single-proof or triple-proof thermal paper involves applying a protective coating layer on standard thermal paper. This process entails sequentially applying the filling layer, color layer, and protective layer onto the base paper.

The structure of high-retention ethanol-resistant thermal paper:

1. Base paper

2. Filling layer

3. Color developing layer

4. Protective layer

Thermal paper developed by Qingdao JIERUIXIN Machinery and Technology Co., Ltd. demonstrates a remarkable color retention rate of >70% after three hours of immersion in ethanol with a volume concentration of 50%.

1. Filling Chemicals and Coating Method:

A mixture of calcined kaolin, CaCO3, polystyrene hollow sphere resin (EPS), lubricant, PVA, starch latex, additives, and water, with a solid content of 40% to 50%, is applied to the base paper using a blade coating machine at a coating weight of 4~12g/m². The thermal pre-coated paper is then formed through drying and calendering.

2. Color Developing Chemicals and Coating Method:

The color-developing layer comprises colorless dye, color developer, and auxiliary materials in specific proportions. Colorless dyes like ODB-2, CVL, etc., are processed to form stable crystalline particles with a particle size of 0.4~0.6μm. The BPA developer is ground into fine particles (0.1~0.3um), and melamine formaldehyde resin (MF) is added to form a pre-polymer solution, followed by heat treatment to produce a suspension of film-coated tiny developer particles. The auxiliary materials include BON, modified polyvinyl alcohol (PVA), calcium carbonate, lubricant, dispersant (PAAS), and starch cooking liquid, mixed with water to prepare a color-developing coating with a solid content of 20% to 40%. This coating is applied onto thermal pre-coated paper using a curtain coating machine at a coating weight of 4~5g/m² and transformed into a thermal color layer through drying and calendering.

3. Protective Chemicals and Coating Method:

The protective layer, also known as the top coating, consists of light calcium carbonate, silica, lubricant, acrylic latex, cross-linking agent, PVA, additives, and water, mixed in specific proportions. This mixture is applied onto heat-sensitive surface coating paper using a curtain coating station, with a coating amount of 1~2g/m², followed by drying and calendering to produce heat-sensitive paper with a protective layer.

Compared to existing technologies, high-retention ethanol-resistant thermal paper exhibits exceptional stability. Even at an ethanol solution volume concentration of 50%, the printed text remains highly recognizable with a high retention rate after three hours of immersion, significantly enhancing the ethanol resistance of thermal paper and addressing the issue of handwriting fading when exposed to organic solvents such as ethanol during usage.