Electronic photography (eIectrophotography) uses static electricity and photoelectric effect to record pictures. Electrophotography has the characteristics of high resolution, reliability, speed, and the ability to use ordinary paper, and its sensitivity is second only to silver salt photography. Therefore, it is often used in the production of ordinary copiers, laser printers, film (photographic) films and the production of offset printing plates. At present, electrophotography is widely used in two ways: Carlson method and electrophotography.
Electrophotographic printing technology
Electronic photography is a very mature and versatile printing technology. It first appeared in 1960 when it was used in office copiers. Its printing process was similar to that of lithography. Typography is very similar. The printing plate is a cylinder or belt covered with a layer of photoconductor (PC). A printed image can be formed on this layer of photoconductor. The printed image is composed of a charged area and an uncharged area. . Both the charged area and the uncharged area will be colored according to the adopted technology, that is, the toning process. The image can be printed on the paper directly through contact or indirectly through a silicone transfer roller or belt (similar to the offset fixing roller in lithography technology). Early copiers used the principle of geometric optics to copy the image of the material to be printed onto the photoconductor; if the principle of geometric optics is replaced with a scanning laser beam or a linear LED array (electronically adjustable), it constitutes today's laser Printer. So far, printing technology has evolved from desktop office printer technology (4-10ppm) to high-speed commercial printer technology (over 100ppm); although commercial printers can achieve size printing performance, it is the largest in color and black-and-white printing The printing width only reaches 8.5～17in.
Electronic photographic printing includes a series of continuous mutual cooperation processes. If high-quality printing effects are to be achieved, these processes must be unified and optimized. The electrophotographic process is shown in the following figure "Electrophotographic Process".
Although some electrophotographic printing systems also use liquid inks, most laser printing systems use dry powdered substances, often called toners, as colorants. Toner is composed of pigments and thermoplastic binder materials (such as polyester, polystyrene, polyamide). Electrophotographic colorants also require carrier particles, called iron powder cores, to transport the colorants through the force of triboelectricity. These iron powder cores are composed of iron oxide particles 5-10 times larger than the diameter of the toner particles of 5-20μm. When the toner particles are transferred to the photosensitive drum or the light guide surface of the photosensitive belt by the potential difference, they return to the ink tank. The toner particles are fixed on the substrate at 150°C and a certain pressure. At this time, the thermoplastic material in it melts and then solidifies together with the pigment through natural cooling.
Application of electrophotographic
Currently, the largest application field of electrophotographic is the copier. Nowadays, electrostatic printing methods using selenium, wet and dry photocopiers using zinc oxide-resin photosensitive layer, equipment using cadmium sulfide, etc., are all put on the market. Electronic copiers are also used to make templates for offset printing. The second is to make color copying. First, the three colors are decomposed, and then developed on the same thick plate three times or the three colors are developed separately and then overlapped three times. These color copies are further divided into a method using photosensitive color toner and a color method using a photoconductive particle film layer. Both methods have the characteristic of only one exposure.
Computer output printing
Compared with other methods, it is more difficult to copy at the same time. It requires special paper and has the disadvantages of developing and fixing indispensable. However, no noise, fast speed, and high reliability, so it has gradually become popular. It can be roughly divided into scanning type and fixed electrode type. However, a scanning device needs to have a text manuscript and scan it to obtain an electrostatic latent image, so it is essentially the same as the aforementioned facsimile. The fixed electrode type can be divided into an electronic recording type and an electrostatic recording type. The former adopts the Carlson method. It has a light source and optical lens system in the shape of a letter board, or a combination of a special cathode ray tube such as a picture tube or a code tube and a lens system to make it image on the selenium photosensitive surface. Another Chinese printing device that combines an optical fiber recording tube with zinc oxide photosensitive paper has also been published.