What Is Electrophotography?

Electrophotography is a general term for copying methods obtained by combining electrostatic principles with photoconductive properties. It is often known under the names of zerography and zinc chloride electrophotography. General photography is called silver salt photography, while electrophotography and diazonium photography are called non-silver salt photography.

Electronic photography (eIectrophotography) uses static electricity and photoelectric effect to record pictures. Electrophotography is high-resolution, reliable, fast, and can use ordinary paper. Its sensitivity is second only to silver salt photography. Therefore, it is often used in the production of ordinary copiers, laser printers, film (photographic) film and offset printing plates. At present, electrophotography is widely used by Carlson method and electrophotography.

Electrophotography is a very mature and versatile printing technology. It first appeared in 1960, when it was used in office copiers, and its printing process was very similar to lithography. The printing plate is a cylinder or a belt, which is covered with a layer of photoconductor (PC). On this layer of photoconductor, a printed image can be formed. The printed image is composed of the charged area and the uncharged area. . Both the charged area and the uncharged area will be colored according to the adopted technology, that is, the color process. The image can be printed directly on the paper by contact or indirectly through a silicone transfer roller or belt (similar to the offset fuser in offset printing technology). Early photocopiers 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 was replaced with a scanning laser beam or a linear array of LEDs (which can be electronically adjusted), 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 Printing width is only 8.5 ~ 17in.

Electrophotographic printing includes a series of continuous and collaborative processes. If high-quality printing effects are to be achieved, these processes must be optimized uniformly. The electrophotographic process is shown below. ^[1]

Although some electrophotographic printing systems also use liquid inks, most laser printing systems use a dry powdery substance, commonly referred to as toner, as a colorant. Toner is composed of pigment and thermoplastic binder materials (such as polyester, polystyrene, polyamide). Electrophotographic colorants also require carrier particles, called iron powder cores, to transport the colorants by the force of triboelectricity. These iron powder cores are composed of iron oxide particles that are 5 to 10 times larger than the diameter of the toner particles of 5 to 20 m. When the toner particles are transferred to the light guide surface of the photosensitive drum or photosensitive belt using a potential difference, they are returned to the ink tank. The toner particles are fixed on the substrate at 150 ° C and a certain pressure. At this time, the thermoplastic substance in the toner is melted, and then the natural pigment is cooled together with the pigment.

Electrophotographic copier

At present, the largest application field of electrophotography is the copier. Nowadays, various products such as electrostatic printing using selenium, wet and dry copying machines using zinc oxide-resin photosensitive layer, and equipment using cadmium sulfide are put on the market. Electronic copiers are also used to make stencils for offset printing. Secondly, for color copying, the three colors are first decomposed and then developed three times on the same thick plate or the three colors are developed separately and then overlaid overprinted three times. These color copies are divided into the photosensitive color toner method and the photoconductive fine particle layer color method, etc. No matter which method has the characteristic of only one exposure.

Electrophotographic computer output printing

Compared with other methods, it is more difficult to copy at the same time. It requires special paper, and it has the disadvantages of indispensable development and fixing. However, no noise, fast speed, and high reliability have gradually spread. Can be roughly divided into two types of scanning type and fixed electrode type. However, the scanning device requires a text original and scans it to obtain an electrostatic latent image, so it is essentially the same as the aforementioned facsimile. Fixed electrode type can be divided into electronic recording type and electrostatic recording type. The former uses the Carlson method. It has a light source in the shape of a letter and an optical lens system, or a combination of a special cathode ray tube and a lens system such as a picture tube, a code tube, etc., to make it image on the selenium photosensitive surface. A Chinese printing device that combines an optical fiber recording tube with zinc oxide photosensitive paper has also been published. ^[3]