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Technological progress: digital printing and ink (II)

the main digital technology electrostatic printing electrostatic printing technology was introduced by Xerox in 1950, so the relaxation experimental machine is particularly important at this time. In principle, it is an analog technology, which is similar to the electrostatic copying technology. With the laser printing technology, it has entered the digital era. The principle is basically the same:

a photosensitive drum, plate or moving conveyor belt is charged with uniform high-voltage charge in the dark; Part of the surface is exposed to light (through copy system, laser scanning, or LED array) and loses charge; The colorant is printed and adhered to the charged part; The graphics are transferred to the final surface and fixed (by thermal fixation); The photosensitive surface is discharged, cleaned and recharged for next use. Figure 2: internal and external views of Saikang International's digital flagship: Saikang 5000 dry powder electrostatic digital printer, with the fastest speed of 8000 A4 pages per hour, double-sided full-color printing

the main electrostatic printing systems and digital printers are used for document and publication printing, using dry powder colorants. However, HP's Indigo printer uses liquid ink, which can simulate the color range of ordinary printing (such as lithography) ink, and change the printing information page by page

although the rise of inkjet has encountered some basic technical problems, inkjet is the most functional digital printing technology, because it is a non-contact printing system, which can use various fuels, pigments and film-forming material/substrate systems on various irregular, easily damaged or curved surfaces, and most of them do not need to be heated during drying. There are many kinds of ink-jet technology. Here we introduce this one as shown in the following figure:

Figure 3: basic operation principle of main ink-jet printing system

continuous ink-jet printing machine is mainly used for marking printing. It can be sprayed on a packaging line, which is expected to be completed and put into production at the end of 2018. It can use low-resolution words and graphics, can be used on curved surfaces that are weaker than eggshells, and can also be used in plastic and extrusion production lines, Or the end of the binding machine, printing the subscription address on the magazine, etc

there are several ways of on-demand ink drop control (DoD) technology, which can be used in high-precision fields

the manufacturing cost of bubble inkjet technology is relatively low, but the nozzle is easy to break. Ideal for office printing, etc., because these occasions rarely require the reuse of ink cartridges. Piezoelectric inkjet technology is widely used in graphics, packaging, textile and industrial and commercial products printing. Many inkjet technologies require low viscosity liquid inks, but tonerjet brand systems use dry powder. These technologies are "binary" - that is, the ink is either in the position of wedge clamp, for example, or not in that position. (high quality printing will use the rear ink drops to overlap the front ink drops). The world's largest supplier of digital printing machines, Saier company, has developed a patented technology - "gray scale" printing nozzle, which can spray ink droplets of 16 different sizes. This enables us to reproduce pictures and other continuous tones more accurately

the speed limit of DoD technology comes from the fact that the nozzle must move from one end to the other. An expensive but more practical method is to use an array of nozzles that cover the entire width of the substrate. Inca digital printing company is a pioneer in this technology. Using its FASTJET brand UV inkjet equipment, it can achieve a speed of 3000 square meters per hour, about 100 meters per minute, on a printing width of 500 mm. This FASTJET technology requires an array of 128 nozzles to eject onemillion ink droplets per second

another high-speed Inca printer is the Columbia turbo brand, which is said to be the world's fastest flat-panel inkjet printer. Using UV curing ink, it can print on an area of 3.2 meters by 1.6 meters, reaching 160 square meters per hour

Figure 4: Inca's Columbia turbo is a great burden for high-speed flat-panel inkjet printing press

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