Digital Printing and Direct Imaging (6)

In principle, ink-jet printing is a high-speed imaging system. According to the different spraying methods, the production speed of ink droplets can vary from several thousand to several hundred thousand droplets per second. However, the high speed of inkjet printing also depends on the specific scanning mechanism. The system adopting the linear array nozzle nozzle has a very high imaging speed and is also a method commonly used by digital printing systems; the speed of imaging using a separate nozzle is very low. , But it is easy to realize large-format imaging, which is a commonly used method for large-format color inkjet (including color digital proofing). At present, the use of ultra-fine pigment ink jet system has begun to appear, so that the weather resistance of inkjet images has been greatly improved, and ordinary paper inkjet technology has gradually matured, the above-mentioned technical difficulties facing the inkjet system may not be far In the future, a better solution will be achieved. The advantages of inkjet printing technology in speed and the characteristics of non-contact imaging will be further reflected. In general, digital press systems using inkjet printing technology have the following features.
● The use of special printing materials is required. Most of the coloring agents are dyes, but they are currently being developed in the direction of pigments and plain paper;
● The number of gradations can achieve multiple values ​​(but limited range);
● Overall quality can only reach the low offset printing level at present. However, it needs to be explained that low quality is not the essence of inkjet imaging technology, but is a compromise between the three factors of quality, speed, and price under current technology conditions. In fact, the ink jet imaging system can achieve extremely high quality. At present, many successful direct digital color proofing systems adopt inkjet imaging methods, and the quality is very high. It can even be used as the contract propagator;
● The speed is very high. It can reach hundreds to thousands of sheets per minute. At present, 2000 sheets/minute can be achieved.
● Low price.
c Electro-coagulation imaging system This is a new imaging method. The electrochemical reaction between the electrodes causes the ink to coagulate (metal ions induce coagulation), so that the ink is fixed on the surface of the imaging cylinder to form an ink image (image area); The ink that did not undergo an electrochemical reaction (ie, a non-image area) was still in a liquid state and could be removed by a mechanical action of a squeegee. Finally, the printing process is completed by transferring the ink fixed on the imaging cylinder to the substrate by the effect of pressure. According to reports, this imaging method can change the pulse width (up to 4 microseconds) in steps of 15 nanoseconds (10-9 seconds) to obtain fixed inks of different areas and thicknesses on the imaging roller, achieving more pixels. Tonal modulation. This imaging method has no special requirements for substrates, and the fixed ink can be transferred to common substrates. The electro-condensation imaging system has the following obvious features:
● Can be imaged on plain paper, using pigments, similar to traditional offset printing;
● The number of gradations can achieve multiple values ​​and have a wide range;
● Comprehensive quality can achieve mid-range offset printing level;
● The speed can reach hundreds of minutes per minute;
● The price is between inkjet imaging and electrophotographic systems.
d Magnetic recording imaging This recording technology uses the same recording principle as the tape recording technology. It relies on the magnetic material's magnetite being oriented in an external magnetic field to form a magnetic latent image, and then using magnetic toner and magnetic latent image. The interaction of the magnetic force between the fields, complete the visualization of the latent image (ie, development), and finally transfer the magnetic toner to the substrate to complete the printing. Due to the limitation of the color of the magnetic material used in the magnetic toner, this imaging system is generally suitable only for making black and white images, and it is not easy to realize a color image. Currently, there are not many digital press systems that introduce magnetic recording and imaging technology. A representative magnetic recording imaging system jointly developed by XeIkOn and NIPSOn has a resolution of 480 DPI. NISPOn is the first company to introduce a digital recording system for magnetic recording systems. The magnetic recording system has the following typical features.
● Can be imaged on ordinary substrates, using pigments, mostly black and white;
● The number of gradations can achieve multiple values ​​(however, the range is narrow);
● The overall quality is only equivalent to the low offset printing level, suitable for black and white text and line printing; (to be continued)