The digital printing system is mainly composed of a prepress system and a digital printing machine, and some systems are also equipped with binding and cutting equipment, thereby eliminating the steps of color separation, imposition, plate making, and trial run. At present, digital printing machines are divided into two camps: on-machine imaging printing (Computer-to-plantCTP or DirectImageDI) and variable data printing (variableimagedigitalpresses). In-machine imaging printing refers to the process of making a plate directly on the printing machine, omitting the intermediate steps of imposition, film-making, printing, and plate-making. From the computer to the printing machine is a direct process; variable data printing means When the printing machine does not stop, continuous printing needs to change the graphics (also called data) of the printed matter, that is, on the premise that the printing process is uninterrupted, different printed graphics are continuously printed. The color digital printing machine based on powder spraying technology is divided into production type and non-production type. Production digital printing presses have industrial mass production capabilities and higher printing speeds and are suitable for long-term operation; the performance and quality of non-production digital printing presses can also meet the basic requirements of printing, but the price is cheaper and the printing speed is slightly lower. Specifically, variable data printing can be divided into the following three categories according to different imaging principles:
1. Electrophotographic (Electrophotographic): also known as electrostatic imaging (xerography) technology, which uses a laser scanning method to form an electrostatic latent image on a photoconductor, and then uses the charge force between the charged toner and the electrostatic latent image to achieve the latent image The function is to transfer the toner image to the substrate to complete the printing, which is the most widely used digital printing technology.
2. Ink-jet printing system: Ink is ejected from the fine nozzle to the substrate at a certain speed, and then the ink image is reproduced through the interaction of the ink and the substrate. According to the form of inkjet, we divide it into drop-on-demandor impulse and continuous inkjet.
3. Other: Electrocoagulation imaging technology (Elcography), magnetic powder imaging technology (Magnctography), electron beam imaging technology (Blectron-Beam Imaging), magnetic powder inkjet technology (TonerJet).
Remarks:
1. On-machine imaging DI printing machine: the offset printing machine is integrated with a printing plate imaging system. The prepared printing plate can be used to print a large number of printed materials with the same content. The printing method is the same as that of traditional offset printing.
2. Continuous inkjet (continuous inkjet): A continuous inkjet system uses pressure to make ink flow through a narrow hole to form a continuous inkjet. The resulting high speed turns the ink flow into small droplets. The size and frequency of small droplets depends on the surface tension of the liquid ink, the applied pressure and the diameter of the narrow holes. When the ink droplet passes through the narrow hole, it is charged with a certain amount of charge, so as to control the drop point of the ink droplet. The charged ink droplets repel or deflect the ink droplets to a desired position on the substrate surface through a set of charge plates. The offset of the ink droplet and the position of the ink dot on the surface of the substrate are determined by the amount of charge when the ink droplet leaves the narrow hole.
3. Drop-on-demand: Also called pulsed ink supply, the difference between on-demand ink supply and continuous ink supply is that the pressure on the ink cartridge is not continuous, only when there is an ink drop There will be pressure, controlled by the digital electrical signal of the imaging computer. Since there is no ink droplet offset, the ink tank and circulation system can be omitted, simplifying the design and structure of the printer. The digital signal is converted into instantaneous pressure by heating or piezoelectric crystal. Piezoelectric technology is one of the simplest ways to generate ink droplets. The piezoelectric effect is used. When the piezoelectric crystal is subjected to tiny electronic pulses, it will expand immediately, and the ink cartridge connected to it will be pressed to generate ink droplets.
The most representative inkjet technology is piezoelectric ceramic technology.
4. Electrocoagulation imaging technology: The basic principle is that the electrochemical reaction between the electrodes causes the ink to coagulate, so that the ink is fixed on the surface of the imaging drum to form an image area, while the ink in the blank area where no electrochemical reaction occurs is still in a liquid state. Then, the ink in the blank area is scraped off by a scraper, so that only the graphic area is fixed on the surface of the cylinder, and then transferred to the substrate by pressure to complete the entire printing process.
5. Magnetic recording digital printing machine: Magnets relying on magnetic materials are aligned under the action of an external magnetic field to form a magnetic latent image, and then use the interaction between the magnetic toner and the magnetic latent image to complete the development process. The toner is transferred to the substrate. This method is generally only suitable for black and white images, and it is not easy to realize color images. Some of Xeikon's products are magnetic recording digital printers.
6. Electrostatic imaging digital printing machine: the electrostatic latent image is formed on the photoconductor by the method of laser scanning, and then the charge force between the charged toner and the electrostatic latent image is used to realize the latent image. Finish printing on the object. This is the most widely used digital printing technology. One of the representative manufacturers uses electronic ink development, represented by HPIndigo. The other is the use of dry toner development, mainly Xeikon, Xerox, Agfa, Canon, Heidelberg, ManRoland, IBM and other companies.
7. Electro-coagulation digital printing machine: The basic principle is that the electrochemical reaction between the electrodes causes the ink to agglomerate, so that the ink is fixed on the surface of the imaging drum to form an image area, and the ink in the blank area where no electrochemical reaction occurs is still in a liquid state. Then, the ink in the blank area is scraped off by a scraper, so that only the graphic area is fixed on the surface of the cylinder, and then transferred to the substrate through the pressure to complete the entire printing process. The representative manufacturer of the electro-coagulation digital printing machine is the product of Elcorsy.
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