1.Concept

Thermal paper is a kind of processing paper, its manufacturing principle is to coat a layer of "thermal paint" (thermal discoloration layer) on high-quality base paper. Although there are more than a dozen chemicals used in this chromophore, there are at least the following compounds: colorless dyes, which have a wide variety of dyes, most commonly used are fluorescent compounds. chromogenic agents account for less than 20%, commonly used are bisphenol and p-hydroxybenzoic acid; sensitizers account for less than 10%, which contain benzenesulfonamide compounds; fillers account for less than 50%, commonly used are calcium carbonate (particles); Adhesives account for less than 10%, such as polyvinyl acetate; stabilizers, such as diphenyl p-phthalate; lubricants, etc. Therefore, the process is difficult and the technical requirements are high.

Thermal paper, also known as thermal record paper, thermal copy paper, and thermal fax paper, is called thermal copy paper in Taiwan. It was first developed by Minnesota Mining Ink Character in 1951.

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

2.Uses

Thermal paper is mainly used in the following aspects: fax machine, communication, medical treatment, measuring system, such as electrocardiograph, thermal instrument, computer network terminal printing, trademark, signature (POS), etc., of which fax machine is the most widely used. With the rapid development of information technology, bills printer technology, and barcode technology have been widely used. Thermal paper has been growing rapidly in the field of barcode recording information and bills printing because of its unique performance, the advantages of fast image generation and convenient barcode labels.

3.Classification

Functionally, thermal paper can be divided into ordinary thermal paper and three-proof thermal paper. Three-proof thermal paper is a protective layer coated on thermal chromophore to give three-proof thermal paper better waterproof, oil-proof and friction-proof performance, mainly for the high-end market.

Structurally, thermal papers are divided into two main categories. One is physical thermal papers which use heat to physically color colored pigments to achieve recording effect. These thermal papers are also divided into melt transparent, melt transfer and thermal sublimation. Among them, melt transparent thermal papers are representative. They are widely used in medical electrocardiogram and electroencephalogram, etc. They are used in Intel. Printing paper for network terminals; in business activities, it is used to make trademarks, signatures (POS) and so on. Among them, fax paper accounts for the largest proportion. The other is the chemical thermal paper, which uses the chemical reaction under the action of heat to achieve the purpose of chromogenic. It is the most widely used product in the market at present. This kind of thermal paper can be divided into two-component metal compound chromogenic thermal paper and two-component non-chromogenic dye thermal paper.

4.Principle of color rendering

The principle of melt transparent thermal paper is that a layer of opaque wax is coated on the black base paper as a surface layer, and the opaque wax material is melted and transparent by the action of the hot pan, and the color of the base paper is exposed to form an image.

The thermal paper color principle of metal compounds is based on the mixture of heavy metal salts and reductants of fatty acids. Fatty acid salts are melted by heating and reacted with reductants so that heavy metals can be reduced and colored freely.

The principle of thermal paper color rendering of colorless dyes is based on the reaction between colorless dyes containing inner aliphatic rings and color reagents under the action of heat.

Most lottery tickets use thermal paper, which is not suitable for long-term preservation, but good thermal paper can be preserved for 30 years or even longer. When the thermal paper is placed above 70 C, the color of the thermal coating begins to change. The cause of its discoloration also begins with its composition.

Thermal components in thermal paper coatings are mainly two kinds: one is a colorless dye or a leuco dye. The other is a color developer. This kind of thermal paper is also called two-component chemical thermal recording paper.

The main colorless dyes are crystal violet lactone (CVL), fluorine system, colorless benzyl methylene blue (BLMB) or spiropyran system in the triphenylalkylphthalide system.

The commonly used dispersants are polyvinyl alcohol L-3266, polyvinyl alcohol GL-05, polyvinyl alcohol KL-03 (synthetic chemical product of Japan).

The commonly used additives for top and bottom coatings are gohsefimer Z-200, polyvinyl alcohol T-350 and polyvinyl alcohol N-300.

The main color reagents are para-hydroxybenzoic acid and its esters (PHBB, PHB), salicylic acid, 2,4-dihydroxybenzoic acid or aromatic sulfone.

When the thermal paper is heated, the colorless dyes react chemically with the developer to produce color. When the thermal paper is used to receive signals on the fax machine or print directly with thermal printer, the pictures and texts are displayed. Because there are many kinds of colorless dyes, the colors of handwriting are different, such as blue, purple-red, black and so on.