The status quo and development trend of digital printing technology

The status quo and development trend of digital printing technology

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Digitalization and networking are the two foundations and themes of today's printing technology development. Throughout the printing industry, a new production environment and technology foundation are being built. Digital printing is a new thing in the development of digital and networked printing technology, and is also a focus of the development of printing technology today.

First, the definition of digital printing

There are many reports and materials that confuse digital printing with digital printing. But in fact, the two are not the same content, it is necessary to explain. From a definitional point of view, digital printing has the following typical characteristics:

1. The digital printing process is a computer-to-paper/print process (Computer-to-Paper/Print), which directly puts digital files/pages

(Digital File/Page) The process of converting to print.

2, the digital printing final image formation process must be digital, without any intermediary simulation process or carrier intervention.

3. The information of digital printed matter is 100% variable information. That is, the two printed products of the adjacent output can be completely different, and can have different layouts, different contents, different sizes, and even can select substrates of different materials. If it is a publication, the binding method can also be different.

Two basic concepts are derived here, one is VariableInformation Printing and the other is Plateless Printing. In fact, in order to achieve 100% variable information printing, no version is necessary. In this sense, the above three characteristics are not independent of each other, but are related to each other. Among the above three features, variable information printing and non-printing are the external features of digital printing, and are most easily accepted by everyone, and are also most familiar to everyone. Some people may ask if digital printing can be classified in the printing category if there is no printing plate. The answer is yes, because in terms of output speed and print quality, there is no difference between digital prints and traditional prints. Perhaps, we don't have to spend time discussing the issue of the attribution of digital printing, because this should not be a problem in itself, but should discuss how to modify the definition of printing itself to adapt to the development and changes of technology.

Second, the system composition of digital printing

In general, the basic composition of a digital printing system is basically the same as that of a traditional printing system, but it is an all-digital production system with its own characteristics.

1. Digital printing is a completely digital production system. The digital flow runs through the entire production process, from the input of information to printing, and even binding output.

2. Digital printing integrates pre-press, printing and post-printing. From the perspective of system control, it is a seamless all-digital system. The digital printing system is like a "combined harvester". The entrance of the system (that is, the input of information) is digital information, and the exit of the system (that is, the output of information) is the information product of the desired form, such as printed matter, books, magazines, and the like. There are many sources of digital information, which can be digital files or images transmitted by the network, information transmitted by the prepress system, or digital information carried by other digital media such as optical disks, optical disks, hard disks, and the like. Moreover, the variety of digital printing products is diverse, from commercial prints to publications, trademarks, cards, and even packaged prints (individualized packaging) covering a wide range of professional fields. The system connection of digital printing systems relies mainly on two methods, namely network and digital media. It is a complete print production system consisting of a control center, digital press, binding and cutting sections. All operations and functions can be pre-set as needed and then automatically completed by the system.

3. Digital printing has on-demand production capacity, and can produce and produce information products that customers need according to specific requirements.

Third, the digital printing production process and technical basis

The traditional printing production process is arranged in the pre-press, printing, post-press, and sales, storage, transportation, and finally in the hands of customers. There is a very strict logical order in chronological order. The entire production process is characterized by the transformation of physical carriers, from manuscripts to digital documents, to film, to plates, and finally to prints, which are converted between different physical carriers. This determines that traditional printing production requires the use of warehousing and transportation to connect and complete different production processes and the transfer, storage and distribution of products and intermediate carriers. Therefore, the traditional printing production is a typical production method based on the technology of “simulation process + storage + transportation”. This mode of production is inevitably limited by time and geography. Digital printing, on the other hand, does not require the necessary prepress processing as traditional printing. However, the digital files formed by prepress processing do not need to be printed immediately, but are stored digitally in the system or through numbers. The network is transmitted to a different location, and finally, the print output is completed according to the customer's order demand. Obviously, this is a brand new production method based on "digital flow + digital media / high density storage + network transmission". Of course, it will not be limited by time and geography like traditional production methods. With the development of technology, in fact, as long as the area covered by the network, no matter how far the distance is, real-time transmission of the product (digital file/page) can be realized, and the output can be printed according to the requirements of the customer. Therefore, it can be said that the conventional printing is a production mode of "reproduction after production", and digital printing is a production mode of "reproduction after sale". Therefore, once digital printing is combined with the network, it can construct a system of on-demand production and service on a global scale to meet the needs of the gradually developed personalized printing and publishing market.

Fourth, the market positioning of digital printing

The market for digital printing is positioned on-demand and on-demand. The on-demand service of information is a trend in the development of information industry today. As a branch of the information industry that provides graphic and information products, printing, publishing and packaging are also developing in this direction, on-demand printing (on -demandPrinting) and On-demand Publishing are typical products of this development. Strictly speaking, on-demand printing on-demand printing should meet the following requirements:

1. At the time the customer needs;

2. At the place where the customer needs it;

3. Print and produce prints/publications that customers need.

Traditional printing is a production method that targets the needs of the masses and wins by quality and price. Its price advantage is achieved by increasing the number of prints. That is, as the number of prints increases, the cost per page is continuously reduced. The root cause is the use of plates, which involve plate making and corresponding consumables costs. In fact, when the number of prints is large, the cost of plate-making and corresponding consumables for each page of prints has been reduced to such an extent that it can be ignored. According to the specific plate-making method, the single-page cost is not the same. The traditional PS plate process is slower due to the high cost of plate making; the cost of the direct plate-making process is lower, and the cost per page is lower. Digital printing is a production method for individual needs, winning by speed, diversity and meeting different needs. Digital printing does not require plate making, and there is no problem of plate cost sharing. Therefore, printing one, ten, 100 and 10,000 sheets will not affect the cost per page. From the perspective of economic costs, digital printing is positioned in the short-run printing market from zero sheets to hundreds of sheets and thousands of sheets. On the other hand, with the continuous improvement of technology and the emergence of new imaging systems, the cost per page of digital printing is also decreasing, and its cost advantage is also moving in the direction of more printing, which makes traditional offset printing a potential The threat of worrying about market share being eaten. This has caused arguments about whether digital printing will replace traditional printing, but in fact the problem is neither so intuitive nor simple.

From the relationship between print quality and quantity, traditional offset printing is positioned in high-volume (long version), high-quality fields, digital printing is positioned in a small number (short version), and the quality is not too high, but now the situation has occurred. Variety. Traditional offset printing is developing in the direction of high quality and short version, and the quality of digital printing is also increasing, approaching the level of high-grade offset printing. In other words, the development trend of the two is the same, in the same market area, that is, the high-quality and diversified short-run market, this trend is in the tradition of using direct plate making, especially offline direct plate-making technology (with version) The performance of offset printing is particularly prominent and obvious, because the rapid increase in plate making speed and the significant reduction in cost enable them to adapt to the short-run market demand. However, regardless of whether the two types of printing will fall into the same field in the future, there is still an essential difference between them: traditional printing is aimed at mass-produced, mass-demand markets; digital printing is aimed at individualization. Produce the market on demand. Some people ask whether the emergence of digital printing will seize the market of traditional offset printing, but it will not. Because the emergence of digital printing will create a new business opportunity, its market is an on-demand market, which is an area that traditional offset printing can not cover. Of course, it is undeniable that digital printing will appear in many areas of traditional offset printing, and even some markets, especially short-run markets (such as fast printing, light printing, etc.) within hundreds of sheets, will become the field of digital printing coverage. But the biggest advantage of digital printing is not in these areas. The areas where it works best are on-demand markets such as on-demand printing and on-demand publishing. If digital printing is used in the same way as fast printing or light printing, this is a huge waste.

The on-demand market is just beginning to develop and develop in foreign countries. There is no such market in China, and it will develop with the development of technology and economy. On-demand demand is huge and potential and needs to be guided and tapped. Perhaps, for our country, while developing existing on-demand printing/publishing technologies, these technologies should be used to drive/drive the development of the on-demand market.

Fifth, the associated family of digital printing

There are many related families of digital printing, such as CTFilm (from computer to film), CTProof (from computer to proof), CTPlate (from computer to printing) and CTPress (from computer to printing), but the closest to digital printing. The in-machine direct platemaking technology, namely CTPress. The earliest in-machine plate-making also required the use of a conventional plate, which was first installed on the plate cylinder of the printing press, and then scanned and imaged on it to complete the plate-making operation. That is to say, in addition to the plate making process being carried out on the printing press, the plate-making method still requires the use of a conventional form of printing plate, which is not substantially different from the conventional offset printing. However, there are two in-machine direct-plate systems at Drupa2000 that are worth mentioning, and they no longer use traditional forms of plates. One is Manroland's DICOweb direct imaging printing system, and the other is Agfa's imaging system called Spray-on-Polymer. DICOweb uses a hot wax transfer imaging method to directly transfer the lipophilic polymer material from the ribbon to the plate cylinder to form a lipophilic image area. After the appropriate treatment, the plate cylinder becomes a hydrophilic non-image area. . The sprayed polymer imaging system directly sprays a polymer material with a change in thermal affinity onto a plate cylinder, and then scans the image by infrared laser scanning. The chemical/physical reaction induced by the temperature rise in the laser-applied region becomes a pro The oil surface, while the area without the laser action, still maintains good hydrophilic properties. After the printing is completed, the polymer coating on the surface of the plate cylinder can be removed by solvent washing, and the plate cylinder can be restored to the initial state, and the next round of plate making can be performed. It should be said that these two systems are already very close to digital printing in use, but they are still the traditional printing method that requires the use of printing plates, do not have the variable information printing function, and do not meet the conditions of the digital printing mentioned above. Although many manufacturers use the concept of "digital printing press" when introducing it, it cannot be called a true digital printing machine. It can only be called "Direct Imaging Press" (DirectImagingPress), or " OnPressImaging, or "On-PressCTP". Digital printing should meet the three necessary conditions mentioned above, that is, (1) is the process from computer to paper or print (Computer-to-Paper/Print), (2) the final ink image formation process is digital (3) 100% variable information printing can be realized, and only a printing machine having such characteristics can be called a digital printing machine (Digital Press or Digital Printer).

Sixth, the key technology of digital printing

In digital printing systems, two technologies are the most critical, one is RIP and the other is the digital press itself. Because digital printing is 100% variable, the two adjacent prints can be completely different and require a high output speed (should be comparable to that of a conventional sheetfed offset press), so RIP is required to be extremely high. Processing speed. In addition. As the quality of digital printing continues to increase, the resolution continues to increase, which further increases the requirements for RIP speed and functionality. A digital press is actually a high-speed hard copy conversion system that converts digital pages at high speed into high-quality color hard copies, or prints. This requires that the high-speed hard copy system used must meet the following requirements:

1, high speed. The printing speed must meet the requirements of thousands or more per hour.

2, high quality. Digital printing should meet or at least approach the quality of traditional offset printing. Otherwise, it is difficult to call it a print, perhaps just a copy or print.

3. Plain paper imaging. There are no special requirements for the substrate, and it can be imaged on ordinary substrates such as paper, film, plastic, etc.

4. Low price. The price should be comparable to traditional offset printing.

Although there are many color hard copy systems that can be selected, there are not many hard copy systems that satisfy the above four conditions.

Resolution is a very important indicator of the quality of a hard copy system, but it is not a completely independent indicator and is related to the tone number. Even if the resolution is not very high, if each pixel has the ability to reproduce a plurality of tone numbers (such as 16th order, 56th order, 256th order, etc.), good print quality can be obtained. Pixel time is the time required to generate a pixel and is a very important indicator for determining the imaging speed of a hard copy system. The scanning speed is a linear length that can be scanned every second when the pixels are arranged according to a certain resolution (for example, 400 dpi), that is, the scanning imaging speed of one-dimensional space.

At present, hard copy systems widely used in digital printing include (1) electrostatic photography; (2) inkjet imaging; (3) electrocoagulation imaging; (4) magnetic recording imaging; and (5) ion deposition imaging. . Electrophotographic systems using dry toner development can achieve resolutions of 600-800 dpi, wet toner development up to thousands of dpi, and the tone number of each pixel can be multi-valued (but limited). If laser scanning imaging with a power of 100 mW is used, the scanning speed of the one-dimensional space is 6.35 m/s, and it can be imaged on a common substrate, and the coloring agent is a pigment, similar to the conventional offset printing. Inkjet imaging has a resolution of 300-1500 dpi, the valence is multi-valued (but limited), and the imaging speed is very high. The imaging time of a single pixel is generally 10-6–10-4 s, and the scanning imaging speed in one-dimensional space It is 0.63-63.5 m/s (scanned at a density of 400 dpi). However, most inkjet imaging uses water-based inks, and the coloring agent is predominantly dyed, and the final image formation depends on the interaction of the ink with the substrate. Therefore, inkjet imaging systems generally require the use of dedicated substrates to achieve the best match of ink and substrate performance. Plain paper imaging with pigments has always been a technical challenge for inkjet systems, and it is also a direction for its development. Electrocoagulation imaging is a new imaging method with a very high imaging speed, with a formation time of 4×10-6 s per pixel and a scanning imaging speed of 15 m/s in one-dimensional space (scanning at 400 dpi density). This imaging method uses an electrochemical coagulation principle to convert an aqueous reaction ink from a liquid state to a solid state, thereby realizing image recording. Although the current resolution of this system is very limited, it can only reach 400dpi, but each pixel has a tone reproduction ability of up to 256 steps, and therefore, has a relatively high quality.

Seven, high-speed method

Table 1 shows the one-dimensional spatial imaging speed of most digital printing imaging systems, but any piece of printed matter is two-dimensional, so it is necessary to find a fast method that can realize two-dimensional spatial recording imaging. Recording systems with different imaging principles can use different methods, but the following methods are more common.

1, photo imaging system (such as electrostatic photography)

This system usually has two high-speed scanning methods. One is to use a high-speed rotating polygon mirror to convert the point source laser beam into a line source laser beam, covering the entire printing surface, and then using the rotary motion of the light guide roller to achieve planar recording; the other is to use a line array LED ( The light-emitting diodes cover the entire printing surface, and then the planar recording is achieved by the rotational movement of the light-guide drum.

2, other imaging systems (such as inkjet, electrocoagulation imaging, etc.)

For imaging methods such as inkjet and electrocoagulation, an imaging element can only cover one point (pixel) or a narrow space. Only a single imaging element can be integrated into a line array to realize planar high-speed recording imaging. Otherwise, it is necessary to achieve planar recording by the round-trip mechanical motion of the imaging element, which makes it difficult to achieve high-speed imaging. For example, for an inkjet imaging system, the nozzle is generally formed into an integrated imaging device of a line array (so-called "multi-mouth" imaging device) so that it can cover the entire printing surface, thereby avoiding the mechanical reciprocating motion of the nozzle. Plane high speed recording imaging.

In the above high-speed method, speed, resolution, and price are always three contradictions, and they are mutually constrained. For example, in order to achieve high quality, it is necessary to increase the integration degree (ie, resolution) of the imaging element, which inevitably leads to an increase in price, and also causes a decrease in speed (because more pixels are required per unit length). In fact, how to coordinate these three contradictions is a very practical technical key to realize the application of digital printing industrialization. The following describes a practical and feasible solution.

The core of this method is to achieve high quality by improving the gradation level reproduction ability of the pixel in the case where the resolution is not too high, so that the speed and price limitation can be avoided skillfully (because there is no need to increase the imaging element) Integration). It is well known that there are three basic methods for reproducing tone at the dot, namely, (1) area modulation dot method, (2) ink film thickness modulation dot method, and (3) dot and thickness simultaneous dot method. Both methods (2) and (3) can achieve high quality under very limited resolution, because the visual quality effect of the final image depends on the resolution and the square root of the number of tones that each pixel can reproduce. The product between (in terms of AM dots), that is, visual quality effect = resolution (dpi) × the square root of the tone number.

The basic practice is to change the integration of imaging elements (pixels). By changing the scanning imaging pulse width or number of pulses applied to each imaging element, the area and thickness of each pixel can be changed within a certain range, thereby realizing the pixel. Multi-level tuning. The degree of multi-level modulation of such pixels depends on the imaging characteristics of the imaging system itself, and some may be less (such as the steep curve in Figure 9), such as electrophotographic and inkjet imaging systems; some may be more (Figure 9 The middle curve is flat), such as an electrocoagulation imaging system. For example, electrophotographic or inkjet imaging systems generally have poor multi-level modulation capabilities, and each pixel can achieve 16 tones (or more), so the 600 dpi visual quality effect is equivalent to 2400 dpi of offset printing (amplitude modulation dots) Elcorsy's electrocoagulation imaging system has excellent multi-level modulation capability, and each pixel can achieve up to 256 tones. The 400dpi visual quality effect is equivalent to the 6400dpi offset effect (amplitude modulation dot).

Eight, digital printing systems and manufacturers exhibited by Drupa2000

Exhibitors of digital systems on Drupa2000 are basically divided into the following categories:

1. Electrophotographic system

There are two basic modes in an electrophotographic system, one is a high resolution system using wet toner development, ie an 800 dpi imaging system, mainly from Indigo, and the other is low in dry toner development. The resolution system, the 600dpi imaging system, mainly includes companies such as Xeikon, Xerox, Agfa, Canon and IBM. These are the manufacturers that are familiar to everyone in the field of digital printing. Two new members are worth mentioning in this exhibition. One is Heidelberg and the other is Manroland. The systems they introduce all use dry toner imaging. Electrophotographic technology (Figure 10). The basic principle of electrophotographic imaging is to form an electrostatic latent image on the photoconductor by laser scanning, and then to visualize the latent image by the Coulomb force between the charged toner (the symbol is opposite to the electrostatic latent image) and the electrostatic latent image. (Development), and finally the toner image is transferred to the substrate to complete the printing. Therefore, this method has the following characteristics:

(1) It can be imaged on plain paper, and the pigment is pigmented, which can realize black and white as well as color, which is very similar to traditional offset ink;

(2), the number of tone can achieve multiple values (but a limited range);

(3) The comprehensive quality can reach the mid-range offset level;

(4), printing speed can reach tens to hundreds of sheets per minute;

(5) However, the price is higher than other imaging systems. The price of an electrophotographic imaging system depends to a large extent on the price of the toner. It is said that the current price of toner is somewhat artificial and is expected to be further reduced.

2, inkjet imaging system

There are not many digital printing systems using inkjet imaging, mainly Scitex and Aprion, with a resolution of 600 dpi. The principle of inkjet imaging is to spray the ink from a fine nozzle (typically 30-50 microns in diameter) onto the substrate at a certain speed, and finally realize the reproduction of the ink image through the interaction of the ink and the substrate (Fig. 11). It is generally required that the solvent and water in the ink can quickly penetrate into the substrate to ensure sufficient drying speed, and the coloring agent (generally mostly dye) in the ink can be fixed as much as possible on the surface of the substrate to ensure a sufficiently high level. Printing density and resolution. Therefore, the ink used must match the substrate to ensure good print quality. This is why a typical inkjet system must use a dedicated ink and substrate (paper), which is a weakness of inkjet imaging systems. As mentioned above, the inkjet imaging system has the following characteristics:

(1) It is necessary to use special printing materials, and most of the coloring agents are dyes, and now they are developing in the direction of pigments;

(2) The number of tones can achieve multiple values (but the range is limited);

(3) The overall quality can only reach the low-grade offset level. But one thing to note is that low quality is not the essence of inkjet imaging systems, which can be a compromise between quality, speed and price. In fact, the inkjet imaging system can achieve high quality. At present, many successful direct digital color proofing systems use inkjet imaging methods, which are of high quality and can be used as a contract (ProtractProof);

(4) The speed is very high, reaching hundreds to thousands of sheets per minute, and it is now possible to achieve 2000 sheets/minute;

(5) The price is low.

3, coagulation imaging

This is a new imaging method in which the ink is agglomerated by the electrochemical reaction between the electrodes (metal ions induce coagulation), so that the ink is fixed on the surface of the image forming roller to form an image region, and no electrochemical reaction occurs (ie, non-image) The ink in the area is still in a liquid state. Then, the liquid ink of the non-image area can be removed by the mechanical action of a squeegee, so that only the fixing ink of the image area remains on the surface of the drum. Finally, the ink adhered to the image forming cylinder can be transferred to the substrate by the action of pressure to complete the printing process. According to reports, this imaging method can change the pulse width (up to 4 microns) in steps of 15 nanoseconds (10-9 seconds) to obtain fixed inks of different areas and thicknesses on the imaging cylinder, achieving multiple steps of pixels. Modulation. This type of imaging has no special requirements for the substrate, and the fixed ink can be transferred to a common substrate. The electrocoagulation imaging system has the following distinct features:

(1) It can be imaged on plain paper, using pigments, similar to traditional offset printing;

(2) The number of tones can be multi-valued and the range is wide;

(3) The comprehensive quality can reach the mid-range offset level;

(4) The speed can reach hundreds of sheets per minute;

(5) The price is between the inkjet imaging and the electrophotographic system.

4, magnetic recording imaging

This imaging technology and the recording technology of the magnetic tape adopt the same recording principle, that is, the magnetic materials relying on the magnetic material are aligned under the action of the external magnetic field to form a magnetic latent image, and then the magnetic force between the magnetic toner and the magnetic latent image is utilized. The interaction, the visualization of the latent image (ie development), and finally the transfer of the magnetic toner onto the substrate completes the printing. The magnetic material used for the magnetic toner is mainly ferric oxide. Since the material itself has a deep color, this method is generally only suitable for producing black and white images, and it is not easy to realize color images. At this exhibition, Xeikon and Nipson launched a magnetic recording imaging system with a resolution of 480 dpi. Nipson is the first company to introduce a digital printing system for magnetic recording systems. In summary, the magnetic recording system has the following characteristics:

(1) It can be imaged on ordinary substrates, using pigments, mostly black and white;

(2) The number of tones can achieve multiple values (but the range is narrow);

(3) The comprehensive quality is only equivalent to the level of low-grade offset printing, suitable for black and white text and line printing;

(4) The speed is hundreds of sheets per minute;

(5) The price is low.

Nine, Drupa2000's technological breakthrough

1. Serialization of digital printing presses

The application fields of early digital printing were mainly limited to very limited fields, such as product specifications, product samples, etc., but this is no longer the case today. The application field of digital printing covers almost all areas of printing professional applications, such as applicable to books. , magazines, packaging, trademarks and cards, etc. Various manufacturers have launched digital printing systems for different application areas, and provide complete system solutions.

2. Heidelberg and Manroland enter the digital printing field

In the previous exhibitions, the manufacturers of digital printing systems were familiar with some old faces, such as Indigo, XeikonXerox, Agfa, etc. Giant companies like Heidelberg seem to be not interested in this field. However, the situation has changed. At the Drupa2000 exhibition, Shanghai Debao and Manroland have launched their own digital printing systems, and they are marching into the field of digital printing. Heidelberg's digital printing system uses a dry toner developed electrophotographic system, named NexPress, which is a collaboration with Kodak. Manroland's digital printing system is a serialized product that is still an electrostatic camera system using dry toner development for different applications. The addition of these large companies reflects their attitude towards this field and reflects the future development of this field.

3, the speed is greatly improved

The output speed (color) of early digital printing systems has been hovering at the level of tens of sheets per minute, but today it can reach hundreds or even more than 1,000 sheets per minute.

4, the quality continues to improve

Although the quality of some digital printing systems is not very high, in general, it has reached or approached the traditional mid-range offset printing level, and is still developing in the direction of high quality, and at the same time, there is a possibility of further improving the quality in terms of technology.

5, the price has dropped significantly

The single-page price (color) of the electrophotographic system has dropped to 0.1-0.2 US dollars (equivalent to 0.8-1.6 yuan), and may fall further in the future; the price of a single page of the inkjet imaging system has dropped to 0.01 US dollars, equivalent to 8 points. The renminbi is completely acceptable.

6, the paper is more applicable

The digital printing system currently available has a very wide range of paper adaptations, and the paper weight is generally 60-300 g/m2, which can be printed from very thin paper to cardboard.

Ten, digital printing tomorrow

The characteristics and advantages of digital printing itself are not the whole content of this technology. In fact, it does not play a unique role as an independent system. However, if digital printing system is combined with digital network, the situation will be It will be different. Once the digital printing system is integrated with a global digital network, it can build a global on-demand production and service system that is independent of time and distance, providing print and publishing where and when customers need it. On-demand services for products, packaging, cards, trademarks and other products.