The working principle of thermal printer is that a semiconductor heating element is installed on the printing head, which can print the desired pattern after heating and contacting the thermal printing paper. Its principle is similar to that of thermal fax machine. The image is generated by heating and chemical reaction in the membrane. This thermal printer chemical reaction is carried out at a certain temperature. High temperature accelerates this chemical reaction. When the temperature is below 60 C, the paper takes quite a long time, or even several years, to turn dark; when the temperature is 200 C, the reaction can be completed in a few microseconds.
The principle of a thermal printer is to coat a transparent film on a light material (usually paper) and turn the film dark (usually black or blue) after heating for a period of time. The image is generated by heating and chemical reaction in the membrane. This chemical reaction is carried out at a certain temperature. High temperature accelerates this chemical reaction. When the temperature is below 60 C, the film takes quite a long time, or even several years, to turn dark; when the temperature is 200 C, the reflection will be completed in a few microseconds. Thermosensitive printers selectively heat the positioning of the thermal paper, resulting in the corresponding graphics. Heating is provided by a small electronic heater on the print head in contact with the thermal sensitive material. The heater is arranged into square points or strips, which are controlled logically by the printer. When driven, a graph corresponding to heating elements is generated on the thermal paper. The same logic circuit that controls heating elements also controls paper feeding, so that graphics can be printed on the whole label or paper.
The most common thermal printer in thermal printers uses a fixed printer head with heating dot matrix. The printer head has 320 square points, each point is 0.25mm x 0.25mm. With this lattice, the printer can place the printing point on any position of the thermal paper. This technology has been used in paper printers and label printers.
Thermosensitive paper is a kind of special coated paper. Its appearance is similar to that of ordinary white paper. The surface of heat-sensitive paper is smooth. It is made of ordinary paper as paper base and coated with a thermochromic layer on the surface of ordinary paper. The thermochromic layer is composed of adhesives, developers and colorless dyes (or dark dyes). It is not separated by microcapsules. The chemical reaction is in a "latent" state. When the thermosensitive paper meets the heated printing head, the color developer at the printing place of the printing head reacts with the colorless dyes to change color and form a picture and text. When the heat-sensitive paper is placed in the environment above 70 C, the color of the heat-sensitive coating begins to change. The cause of its discoloration also begins with its composition. There are two kinds of thermosensitive components in the coating of thermosensitive paper: one is colorless dye or leuco dye, the other is colour developer. This kind of heat-sensitive paper is also called two-component chemical heat-sensitive recording paper.
The main colorless dyes are crystal violet lactone (CVL), flurane system, colorless benzoylmethylene blue (BLMB) or spiropyran system in triphenylalkylphthalide system. The main color reagents are para-hydroxybenzoic acid and its esters (PHBB, PHB), salicylic acid, 2,4-dihydroxybenzoic acid or aromatic sulfone. When the thermosensitive paper is heated, the colorless dyes react with the developer to produce color.
When the thermosensitive paper is used to receive signals on the fax machine or print directly with the thermosensitive printer, the pictures and texts are displayed. Because there are many kinds of colorless dyes, the colours of handwriting are different, such as blue, purple-red, black and so on.
Thermal printing technology was first used in fax machines. Its basic principle is to convert the data received by printers into dot matrix signals to control the heating of thermal units and to develop thermal coatings on thermal paper. Thermal printers have been widely used in POS terminal systems, banking systems, medical instruments and other fields. Thermosensitive printers can only use special thermal paper. Thermosensitive paper is coated with a coating which will produce chemical reaction and discoloration when heated. It is similar to photographic film. However, this coating will discolor when heated. Thermosensitive printing technology emerges by utilizing this characteristic of thermal coating.
The key of thermal printing technology lies in heating elements. There is a row of tiny semiconductor elements on the core of thermal printer. These elements are arranged closely, ranging from 200 DPI to 600 dpi. These elements will produce high temperature quickly through a certain current. When the coating of thermal paper meets these elements, the temperature will rise in a very short time. As the temperature rises, the coatings on the thermal paper will react chemically and show color.
After the thermal printer receives the print data, it converts the print data into bitmap data, and then controls the current of the heating element on the printer core according to the dot of the bitmap data, thus transforming the print data into the print content on the printing paper.