Widely used in logistics, lottery, medical and ticket fields, thermal paper is a readable information recording material. Distinguished from the use of the field, thermal paper can be divided into unprotected layer of thermal paper and thermal paper with a protective layer. No protective layer of thermal paper is commonly used in restaurants, cash registers and other fast consumer areas, the paper protection performance is poor, easy to scratch the color, ethanol, oil and even soak in water are easy to fade. Thermal paper with protective layer has the advantages of not easy to collision scratch and good waterproof, oil and ethanol, and is widely used in the welfare lottery industry, logistics labeling industry and tickets and other industries.

China's national standards for thermal paper stipulate that under normal temperature and pressure, the color retention rate of thermal paper must be ≥60% after being soaked in ethanol with a volume concentration of 25% for 3 hours through the liquid trap method. At present, the ethanol-proof retention rate of thermal paper on the Chinese market is basically 60%±10%. However, increasing the concentration of ethanol, increasing the temperature of the detection environment and extending the contact time with ethanol will greatly reduce its retention rate and the printed information will fade.

Single-proof or triple-proof thermal paper is to add a layer of protective coating on the basis of ordinary thermal paper. As shown in the Figure, apply the filling layer, color layer and protection layer to the base paper in sequence.

The structure of high retention ethanol-resistant thermal paper

1-Base paper      2-Filling layer      3-Color developing layer    4-Protecting layer

The ethanol-proof thermal paper made by our company Qingdao JIERUIXIN machinery and technology CO.,Ltd has a color retention rate of >70% after being soaked in ethanol with a volume concentration of 50% for 3 hours.

1. Filling chemicals and coating method

Calcined kaolin, CaCO₃, polystyrene hollow sphere resin (EPS),lubrication,PVA, starch latex, additives and water are mixed in proportion to prepare a coating with a solid content of 40% to 50%. Use a blade coating machine to apply it on the base paper with a coating weight of 4~12g/m². Then the thermal pre-coated paper is formed by drying and calendering.

2. Color developing chemicals and coating method.

The color-developing layer is composed of the colorless dye, color developer and other auxiliary materials, which are respectively 10~20 parts, 20~30 parts and 30~50 parts by mass.

Colorless dyes include ODB-2, CVL, etc. and are formed into stable crystalline particles through grinding and heat treatment processes. The particle size is 0.4~0.6μm. The BPA developer is ground into fine particles with a particle size of 0.1~0.3um through a grinder; melamine formaldehyde resin (MF) accounting for 2%~10% of the absolute dry weight of the developer is added to the high-speed dispersion to form a pre-polymer solution is finally heated to 90~100℃ for heat treatment to form a suspension of film-coated tiny developer particles. The auxiliary materials are BON, modified polyvinyl alcohol (PVA), calcium carbonate, lubricant, dispersant(PAAS) and starch cooking liquid. Mix and add water to prepare a color-developing coating with a solid content of 20% to 40%. Use a curtain coating machine to apply the color coatings on the thermal pre-coated paper with a coating weight of 4~5g/m², and is processed into a thermal color layer through drying and calendering.

3. Protecting chemicals and coating method.

The protective layer is the outermost coating of thermal paper, also called top coating. The coating chemical is composed of light calcium carbonate, silica, lubricant, acrylic latex, cross-linking agent, PVA, additives and water mixed in proportion. Mix and add water to prepare a coating with a solid content of 10%~20%. Use a curtain coating station to apply it on the heat-sensitive surface coating paper. The coating amount is 1~2g/m². Then after drying and calendering to produce the Heat sensitive paper with a protective layer.

Compared with existing technologies, high retention ethanol resistant thermal paper has excellent stability. Even if the volume concentration of ethanol solution reaches 50%, the printed text on the thermal paper is excellent recognizable and has high retention rate after soaking for 3 hours, significantly improving the ethanol resistant ability of thermal paper and solving the problem of handwriting fading when encountering organic solvents such as ethanol during use.