Second, digital printing principle classification
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 steps such as color separation, imposition, plate making, and trial running. Digital presses currently fall into two camps: Computer-to-plant (CTP or Direct Image/DI) and variable image digital press. On-machine imaging printing refers to the process of making plates directly to the printing machine, omitting steps such as making imposition, printing, printing, and loading plates. It is a direct process from computer to printing machine; variable data printing refers to In the case of printing without stopping the machine, continuous printing of graphics (ie, so-called data) is required to change the prints, that is, continuously printing different printed images without interruption of the printing process. Color digital printing machines based on dusting technology are also divided into production and non-production type. The production digital printer has industrialized mass production capacity and high printing speed and is suitable for long-time operation; the performance and quality of the non-production digital printer can also meet the basic requirements for 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 (electrophotography): Also known as electrostatic imaging (xerography) technology, the use of laser scanning method to form an electrostatic latent image on the photoconductor, and then use the electrostatic force between the charged toner and the electrostatic latent image to achieve the latent image, The role of the toner image transferred to the substrate to complete the printing, is the most widely used digital printing technology.
2. Ink-jet printing system: The ink is ejected onto the substrate from a fine nozzle at a certain speed, and then the ink image is reproduced through the interaction between the ink and the substrate. According to the form of ink jet, we divide it into: dro-on-demand or imperfection and continuous inkjet.
3. Others: Elcography, Magnctography, Bron-Beam Imaging, TonerJet.
Note:
1. In-machine imaging DI printing press: The essence is that the offset printing machine integrates the printing plate imaging system, and the prepared printing plate can be used to print a large number of prints of the same content, and the printing mode is the same as the traditional offset printing.
2. Continuous inkjet: A continuous inkjet system uses pressure to create a continuous stream of ink through narrow holes. The resulting high speed makes the flow of ink 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 hole. When the ink droplet passes through the narrow hole, it is charged with a certain amount of charge to control the drop point of the ink droplet. The charged ink droplets are repelled or deflected by a set of charge plates to the desired position on the surface of the substrate. The ink droplet offset and the ink dot position on the surface of the substrate are determined by the charge amount when the ink droplet leaves the narrow hole.
3, on-demand inkjet (dro-on-demand): also known as pulse to ink, the difference between on-demand ink supply and continuous ink supply is that the pressure on the ink tank is not continuous, but only when the ink droplets need There will be pressure, controlled by the digital electrical signals of the imaging computer. Since there is no ink droplet displacement, the ink tank and circulation system can be omitted, simplifying the design and structure of the printer. The digital signal is turned into instantaneous pressure by heating or piezoelectric crystals. Piezoelectric technology is one of the simplest ways to create droplets. With the piezoelectric effect, when the piezoelectric crystal is subjected to a tiny electron pulse, it will immediately expand, causing the associated ink tank to be pressurized to produce droplets. Among them, the most representative ink jet 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, and the ink in the blank area where no electrochemical reaction occurs is still liquid. Then scrape the ink in the blank area through a scraper to make the surface of the cylinder only with the ink fixed in the graphic area, and then transfer the pressure to the substrate to complete the printing process.
5, magnetic recording digital printing machine: rely on the magnetic material of the magnet in the external magnetic field under the orientation of the magnetic field to form a magnetic latent image, and then use magnetic toner and magnetic latent magnetic field interaction between the completion of the development process, and finally the magnetic The toner is transferred to the substrate. This method is generally only suitable for black and white images, and it is difficult to implement color images. Some of Xeikon's products are magnetic recording digital printers with a resolution of 480 dpi.
6, electrostatic imaging digital printing machine: the use of laser scanning method to form an electrostatic latent image on the light conductor, and then use the electrostatic charge between the charged toner and electrostatic latent image force to achieve latent image, the role is to transfer the toner image to the printer Finish printing on the object. This is the most widely used digital printing technology. One of the representative manufacturers is the use of electronic ink development, resolution up to 800dpi, represented by HP Indigo. The other is the use of dry toner development, resolution 600dpi, mainly Xeikon, Xerox, Agfa, Canon, Heidelberg, ManRoland and IBM and other companies.
7. Electro-condensing digital printing machine: The basic principle is that the electrochemical reaction between the electrodes causes the ink to coagulate, so that the ink is fixed on the image drum surface to form the image area, and the ink in the blank area where no electrochemical reaction occurs is still in the liquid state. Then, the ink in the blank area is scraped off by a squeegee, so that only the ink in the image area is fixed on the surface of the drum, and then the pressure is transferred to the substrate to complete the entire printing process. The representative manufacturer of the electro-condensing digital press is Elcorsy's product with a resolution of 400 dpi.
Author / Qi Qi Source: "Guangdong Packaging" (2005, Issue 5)