Mainstream digital printing technology

In the era of rapid printing of short prints, digital printing technology has become more and more popular. However, the development of digital printing in our country has not been smooth and has encountered many obstacles during the period. Although digital printing has also gradually matured, it accounts for a small proportion of our total printing business. On the one hand, the overall level of domestic offset printing prices is lower than that of digital fast printing, which makes the advantages of digital printing in terms of price and production cycle not fully exerted. At the same time, the advantages of digital printing and personalized printing have not been fully developed. Many people still print on digital printing. The concept is rather vague; on the other hand, due to the certain differences between digital printing and traditional printing products, it has caused misunderstandings in product identification and printing requirements, which also lags behind the development of digital printing in China. In general, since 2004, digital printing has only gradually become hot in China, but it is only at its infancy. Many people still have doubts and confusion about it. This article describes the current mainstream digital printing technologies in order to allow more people to understand digital printing technology.

1. The concept of digital printing

Digital printing, in a broad sense, means that any device that is connected to a computer and can be printed directly without a plate can be called digital printing. In the narrow sense, digital printing is a new type of printing technology that uses the prepress system to transfer graphic information directly to the digital printer through the network and print out color prints. Nowadays, several mainstream digital printing technologies include inkjet imaging, electrostatic imaging, magnetic recording imaging, direct imaging (DI), and electrocoagulation imaging.

2. Several mainstream digital printing technologies

(1) Ink-jet imaging digital printing

Inkjet printing refers to the use of ink at a certain speed from the fine nozzle to the substrate, and then through the interaction of the ink and the substrate to achieve ink image reproduction, the imaging principle is that the ink at a certain speed from the fine nozzle ( Generally the diameter of 30 ~ 50 μ m) sprayed on the substrate, and finally through the interaction of the ink and the substrate to achieve ink image reproduction. Generally, the solvent and water in the ink can quickly penetrate into the substrate to ensure sufficient drying speed. It is required that the coloring agent in the ink be fixed on the surface of the substrate as much as possible to ensure a sufficiently high printing density and resolution. Therefore, the ink used must match the substrate to ensure good print quality. In the early days, continuous inkjet was used as the main equipment. The nozzles continuously drip ink according to a certain rule. If the ink drops do not need to be printed on the paper, the ink is ejected electrostatically and recycled to the ink tank. This method is not efficient because it only developed ink drop-on-demand technology. The ink jet head went to the place where it needed to be printed. Because inkjet heads can be replaced, many manufacturers mass-manufactured, and they are advantageous in terms of replacement and price. Therefore, ink-jet printing equipment mainly uses drop-on-demand ink technology, and continuous inkjet ink-jet heads must be integrated by printer manufacturers as a whole. Made, so it is not universal. In the field of ink-jet printing, inkjet printers mostly appear as the color output terminals of personal computers. The requirements for quality and speed are not very high, but they are convenient, maintenance-free, and inexpensive.

Medium and large-format inkjet printing technology is mainly used in digital proofing and inkjet, and other major manufacturers include Epson, HP, Kodak, and Roland. In the field of digital proofing, ink jet printing is replaced by offset printing proofing and thermal transfer proofing with its quality advantages. In the field of digital printing, two mainstream systems, electrostatic photography (toner) and inkjet imaging, are mainly used. Variable data printing, publications, personal samples, direct mail printing, commercial printing, label printing, trademark printing, and even security printing; in the area of ​​large-format inkjet printing, large-format printing of all indoor and outdoor displays, advertisements, posters, etc. It is mainly produced by screen printing, offset printing and inkjet imaging. Screen printing is more suitable for producing more than 400 sheets of leaflet jobs. However, from the current market, 200 sheets of leaflets are The market demand is even greater. With the increase of multi-categories and small batches of live jobs, the traditional way of screen printing is greatly limited.

In ink-jet printing, water-based inkjet and paper-based substrates occupy the major market share for large-format inkjets, but the proportion of solvent-based inks and UV-curable inkjets is rapidly expanding, from environmental protection, substrate adaptation From a sexual point of view, UV-curable ink jets are likely to become the mainstream of the large-format color market in the future.

(2) Xerography Digital Printing

Electro-photographic (electro-photographic), also known as electrophotography, is based on the principle of laser scanning to form an electrostatic latent image on a photoconductor, and then uses the Coulomb force between the charged toner and the electrostatic latent image to realize latent image. Visualization, the final transfer of the toner image to the substrate to complete the printing.

In the digital printing industry, digital printing technology for static film printing is much more mature than ink-jet technology. At the same time, it is also one of the most widely used and most flexible forms of digital equipment. There are two basic modes in an electrophotographic system. One is a high-resolution system using wet toner development. Generally, an 800 dpi imaging system is used. The main representative product is Indigo's digital press; the other is dry type. The toner-developed low-resolution system uses a 600 dpi imaging system, mainly from companies such as Xeikon, Xerox, Agfa, Canon, Heidelberg, ManRoland, and IBM.

In general, the application of electrostatic printing systems is relatively flexible, and it is basically not limited by the amount of print. It is mainly used in markets such as on-demand printing and variable data printing. It has not only been applied in the fields of commercial rapid printing and printing in the government, but also applied in fields such as finance, telecommunications, insurance, publishing and printing, packaging and printing.

(3) Magnetic Recording (Magnography) Digital Printing

Magnetic recording imaging technology and magnetic tape recording technology adopt the same recording principle, that is, the magnetism of magnetic material is aligned under the action of an external magnetic field to form a magnetic latent image, and then magnetic toner and magnetic latent image are used again. The interaction of the magnetic force, the visualization of the latent image, and finally a printing method of transferring the magnetic toner to the substrate.

The magnetic material used for the magnetic toner is mainly iron oxide, and the material itself has a deep color. Therefore, this method is generally suitable only for producing black-and-white images, and it is not easy to realize color images. Magnetic recording products are mainly used for the printing of marketable securities, lottery tickets, various bills, business forms, labels and magnetic barcodes; due to the limitations of their production, the printing methods are mainly applied to black-and-white images; at the same time, they are adjustable. The number of gradations can only be within a limited range, and its overall quality can only be equivalent to the low grade of offset printing. Compared with traditional screen printing, due to the special nature of magnetic recording and printing methods, despite its high color density, it has certain requirements for toners and substrates, and thus lacks flexibility.

(4) DI(Direct Image) digital printing

The DI digital printing system is essentially an imaging system in which the offset printing machine integrates the printing plate. The prepared printing plate is used to print a large number of prints of the same content, and the direct plate printing technology is used to directly print the printing plate graphic information. From the computer to the printing plate installed on the printing plate, once complete the plate making and printing technology. The printing method is the same as traditional offset printing.

The DI printing system has the characteristics of short print preparation time, rapid printing (tens of thousands per hour) and high print quality. The market is mainly targeted at print jobs of around 5000 impressions. This 5,000 or so prints are too large for other types of digital presses and too small for traditional prints. Under the premise of guaranteeing the printing quality, it can greatly speed up the printing speed, at the same time, it also has advantages of offset printing and digital printing. Its main representatives are Heidelberg's Quickmaster-DI46-4 and Speedmaster-DI, Manroland's web digital printing press Dicoweb. Komori and NetScreen also have their own DI digital presses.

Despite the rapid development of foreign DI printing systems, the application in China is not very satisfactory and there is a general situation that the utilization rate of equipment is low. This is mainly due to the high investment cost of DI equipment and the high cost of its consumables. At the same time, DI printers cannot print variable data because they are different from devices such as static electricity and ink jet printers.

(5) Coagulation imaging digital printing

The basic principle of the electrocoagulation imaging technology is that the ink is condensed by the electrochemical reaction between the electrodes, so that the ink is fixed on the imaging drum to form an image area. The ink in the blank area where no electrochemical reaction takes place is still liquid, and then passes through. The mechanical action of a squeegee scrapes the ink in the blank area, leaving the surface of the cylinder with only the ink fixed in the image area, and finally transfers the ink fixed on the imaging cylinder to the substrate through pressure, thereby completing the entire printing process. .

The electrocoagulation imaging technique can vary the pulse width in steps of 15 nanoseconds to obtain fixed inks of different areas and thicknesses on the imaging cylinder to achieve multi-level modulation of the pixels. This imaging method has no special requirements on the substrate, so that the ink can be transferred to a common substrate.

Electro-condensed digital presses are represented by Elcorsy products with a resolution of 400 dpi. The electro-condensation imaging system is similar to traditional offset printing in that it can be imaged on plain paper. Unlike pigment printing technology, the number of adjustments in the number of tones can be widened, and a range of values ​​can be achieved. Basically, Achieve mid-range offset printing.

3. The prospect of digital printing

Digital printing is a high-tech printing technology developed in the 1990s. Since Israel's Indigo and Belgium Xeikon launched the first color digital printing machine in 1993, more and more large multinational companies have introduced digital printing machines. Digital printing technology has now developed more maturely. Digital printing has developed rapidly in Europe and America in recent years. Manroland Germany and KBA, which are leaders in the production of traditional printing presses, have also actively launched serialized products for digital presses. The world's leading printer manufacturers have entered the field of digital printing, reflecting the future of digital printing technology. There will be broad prospects for development.

The development of the printing industry is moving towards short editions and variable data printing. The printing industry is also launched with the concept of service. Personalized printing is one of the service concepts. Digital printing technology is becoming more and more mature and eye-catching in a way that is different from traditional printing technologies. At the same time, because the digital printing development is based on a new concept of the development of the market, and the traditional printing business is also essential differences, so I believe that as China's printing business to the short version, rapid, personalized development of the field, digital printing will rely on Its huge market potential, and gradually reduce production costs, China's digital printing will also form an industry, and can get rapid development.