The working principle of a thermal printer is that a semiconductor heating element is installed on the print head. After the print head is heated and contacts the thermal printing paper, the desired pattern can be printed. The principle is similar to that of a thermal fax machine. The image is generated by heating to produce a chemical reaction in the film. This thermal printer chemical reaction is carried out at a certain temperature. High temperature will accelerate this chemical reaction. When the temperature is lower than 60 ℃, the paper needs to take a long time, even up to several years to become dark; and when the temperature is 200 ℃, this reflection will be completed within a few microseconds.
principle
The principle of the thermal printer is to cover a light-colored material (usually paper) with a transparent film, and after heating the film for a period of time, it becomes dark (generally black, but also blue). The image is generated by heating to produce a chemical reaction in the film. This chemical reaction is carried out at a certain temperature. High temperature will accelerate this chemical reaction. When the temperature is lower than 60 ℃, the film needs a long time, even up to several years to become dark; and when the temperature is 200 ℃, this reflection will be completed within a few microseconds.
The thermal printer selectively heats the heat-sensitive paper at a specific position, thereby generating a corresponding pattern. Heating is provided by a small electronic heater on the printhead that is in contact with the thermally sensitive material. The heaters are arranged in the form of square dots or strips and are logically controlled by the printer. When driven, a pattern corresponding to the heating element is generated on the thermal paper. The same logic circuit that controls the heating element also controls the paper feed, so that graphics can be printed on the entire label or paper.
The most common thermal printer uses a fixed print head with a heated dot matrix. The print head has 320 square dots, each of which is 0.25mm x 0.25mm. Using this kind of dot matrix, the printer can print dots on any position of the thermal paper. This technology has been used in paper printers and label printers.
application
Thermal printing technology was first used in facsimile machines. The basic principle is to convert the data received by the printer into a dot matrix signal to control the heating of the thermal unit and heat the thermal coating on the thermal paper for development. At present, thermal printers have been widely used in POS terminal systems, banking systems, medical instruments and other fields.
Thermal printers can only use special thermal paper. The thermal paper is coated with a layer that will undergo a chemical reaction and change color when exposed to heat, similar to a photosensitive film, but this layer will change color when exposed to heat. With this characteristic of thermal coatings, thermal printing technology has emerged.
The essential
The key to the thermal printing technology is the heating element. There is a row of tiny semiconductor elements on the thermal printer core. These elements are arranged very densely, ranging from 200dpi to 600dpi. These elements will quickly generate high temperature when passing a certain current. When the coating of thermal paper meets these elements, the temperature will rise in a very short time, and the coating on the thermal paper will chemically react and show color.
After receiving the print data, the thermal printer converts the print data into bitmap data, and then controls the heating element on the printer core to pass current according to the points of the bitmap data, so that the print data becomes the print content on the printing paper.
Thermal Paper
Thermal printers can only use special thermal paper. The thermal paper is coated with a layer that will undergo a chemical reaction and change color when exposed to heat, similar to a photosensitive film, but this layer will change color when exposed to heat. With this characteristic of thermal coatings, thermal printing technology has emerged.
Thermal paper is a special coated paper with a similar appearance to ordinary white paper. The surface layer of the thermal paper is smooth, and it is made of ordinary paper as the paper base, and a layer of the thermal coloring layer is coated on the surface of the ordinary paper. The coloring layer is made of adhesive, developer, colorless dye (or It is called leuco dye) and is not separated by microcapsules, and the chemical reaction is in a "latent" state. When the thermal paper encounters a heat-generating print head, the developer at the place where the print head prints and the leuco dye react chemically to change color, forming a graphic.
When the thermal paper is placed in an environment above 70 ° C, the thermal coating begins to change color. The reason for its discoloration also starts from its ingredients. There are two main types of heat-sensitive components in the coating of thermal paper: one is a leuco dye or leuco dye; the other is a developer. This type of thermal paper is also called two-component chemical type thermal recording paper.
Commonly used as leuco dyes are: crystal violet lactone (CVL) of tribenzylphthalide system, fluorane system, colorless benzoylmethylene blue (BLMB) or spiropyran system and other substances. Commonly used as color developers 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 dye reacts with the developer to produce a color, so when the thermal paper is used to receive a signal on a fax machine or printed directly with a thermal printer, the graphics and text are displayed. Since there are many varieties used as leuco dyes, the colors of the handwriting appearing are different, including blue, magenta, black and so on.
classification
Thermal printers can be divided into line thermal (Thermal Line Dot System) and column thermal (Thermal Serial Dot System) according to the arrangement of their thermal elements. Column type thermal is an early product, which is mainly used in occasions where the printing speed is not required, and domestic authors have used it in its products. Line thermal is a technology in the 1990s, and its printing speed is much faster than column thermal, and the fastest speed has reached 220mm / sec. To achieve high-speed thermal printing, in addition to selecting a high-speed thermal print head, you must also have a corresponding control board to cooperate with it.
Pros and cons
Compared with the needle printer, the thermal printing speed is fast, the noise is low, the printing is clear, and the advantages of convenient use. However, the thermal printer cannot directly print the duplex, and the printed documents cannot be permanently stored. If the best thermal paper is used, it can be stored for ten years. The needle printing can print double, and if you use a good ribbon, the printing documents can be stored for a long time, but the needle printer has a slow printing speed, high noise, and rough printing. You need to change the ribbon frequently. If the user needs to print the invoice, it is recommended to use pin printing, and other printing other documents, it is recommended to use thermal printing.
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