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I. GTO-DI/SPARC The first DI press in the world was the GTO-DI/SPARC press that Heidelberg pioneered in 1991. This is a DI printer that has been improved on the basis of the original GTO press, so it still adopts the modular structure on the traditional GTO press. The difference is that the waterless offset printing process is used, so the wetting device is removed and the direct plate making device is installed in the space where the wetted device was originally installed. The waterless offset printing plate is coated on the plate base with an ink receptive layer, an opposite electrode layer and an ink repellent layer. Figure 1 shows the imaging principle of this platemaking device. The imaging device arranges 16 electrodes along the circumferential direction of the plate cylinder. When imaging, according to the characteristics of the image distribution, a large amount of electric charges are selectively carried on the 16 electrodes, so that the electrode and the counter electrode layer of the printing plate There is a very high voltage between them. Under the action of this voltage, the air between the electrode and the plate is ionized to generate an electric spark, and the ink repellent layer and the counter electrode layer of the outer layer of the plate are etched away to expose the ink-receptive layer inside, and thus the ink is repelled. The printing plate has created an ink-friendly graphic area. This technique is called spark erosion technology. The shape of dots produced by this spark erosion technique is very irregular, the edges are not clear, the resolution can only reach 1024 dpi, and it has great defects in restoring the color and gradation of the original image and cannot be used to print high quality. Prints were quickly replaced by other imaging technologies. However, this type of printing press has played a large role in the development of the fast printing market for some printing companies.
Second, GTO-DI/LASER this type of printing machine uses laser ablation technology instead of spark erosion technology, made of the printing plate has both fine mesh screen point and high resolution. In order to save costs, this printer uses a cheaper laser diode as the exposure light source, its wavelength is about 830nm, and the corresponding printing plate uses a thermal ablation waterless offset printing plate. The structure of this plate making device is shown in Figure 2b. In the drum axis direction, 16 imaging modules are arranged in sequence. Each imaging module consists of a laser diode, an optical fiber, and an optical imaging element. The precision optical imaging element ensures that the image resolution on the plate can reach 1270 dpi, and the diameter of the pixels can be as small as 30 μm. As the plate cylinder rotates, the optical imaging element moves axially, and each optical element is moved by a distance equal to the spacing between the two optical elements. This is very different from the previous printing machine that used the spark erosion technology to image. In the former, since the electrodes are arranged along the rotation direction of the drum, the plate-making device must move the entire axial distance of the drum. Of course, with the axial arrangement, it is necessary to have a precise control system to ensure strict alignment between the various optical elements.
Figure 2a shows the structure and imaging principle of this printing plate. The plate was made of a 0.18 mm aluminum plate as a substrate, and an extremely thin heat-absorbing layer (≤1 μm) and a silicon layer of about 3 μm in thickness were coated on the surface thereof. The surface of the silicon layer has ink repellency. At the time of plate making, the endothermic layer absorbs the energy of the laser pulse, reaches a certain intensity and volatilizes, and the outer silicon layer is ablated away, exposing the aluminum plate base, and the surface of the aluminum plate base has ink affinity. This waterless offset printing plate was made.
Third, QM DI 46-4 This is Heidelberg and the company launched in 1995 the third generation of DI printing presses. Due to its outstanding improvement in many aspects, the performance of the machine has been significantly improved. The printing speed was increased from 8000 prints/hour at GTO-DI/LASER to 10,000 print/hour, and the print preparation time was reduced from about 20 minutes to about 10 minutes. As a result, the product quickly replaced the second-generation product and occupied the market. This is also the most successful DI product on the market. Among the more than 1,600 DI printing machines in operation, QM DI 46-4 accounted for more than 1,500 units.
The advantages of QM DI 46-4 mainly focus on the following points:
1. A change in the modular structure adopted by GTO presses in the past, using a satellite structure. The impression cylinder is a four-fold diameter cylinder. Four groups of bite bars are designed on the impression cylinder. Each time the impression cylinder rotates, the plate cylinder and the blanket cylinder rotate respectively for four weeks, and four prints can be printed. The impression cylinder can complete all four-color printing with one bite of paper. Its greatest advantage is to make the machine's floor space greatly reduced, which is very important for some fast printing companies that do not have a dedicated large-scale printing shop.
2. The plate used in the GTO DI press is similar to the traditional PS plate, which is an aluminum plate, while the plate used in the QM DI 46-4 press is a polyester plate. The way they handle plates is completely different. The working process of loading and unloading printing plates by the GTO DI printer is: when replacing the printing job, the printed plates need to be manually disassembled, and the four unexposed plates are replaced, and then the plates are imaged using a direct plate-making device; and QM The DI 46-4 press does not require manual exchange of the plate because it uses a roll type plate. When the plate is replaced, the axis can be started by pressing the button and the old plate can be rolled up. The new unexposed plate is fixed on the plate cylinder. A roll of printing can print 35 prints continuously. When the printing plate is used up, it can be replaced with a new roll. Used plates can also be recycled for reuse.
3. A blanket cleaning device is installed on the blanket cylinder, eliminating the need for manual cleaning of the blanket.
4. A printing plate cleaning device is mounted on the plate cylinder to clean the ink on the plate and the debris left in the plate making process. Not only reduces the labor intensity of the workers, but also makes the layout cleaner.
Fourth, Dominant DIDI technology is first applied in the eight-opening printing press. With the maturity of DI technology, some printer manufacturers are aware of the broad prospects of applying this technology to large format printing presses. They have conducted in-depth research on related technologies and have successively introduced four-format DI printing machines.
The earliest launch of the DI Kai DI is the DominantDI produced by ADAST in the Czech Republic. Like the QM DI 46-4, its plate-making equipment uses the thermal ablation technology of Presstek, so its structure and working principle are the same as those of the QM DI 46-4. ADAST then used this technology on its other products, such as the octal 400DI press.
It should be noted that when the printer manufacturers are developing DI printers, they often use the plate making technologies of other manufacturers like Heidelberg and Adalst. Therefore, there are manufacturers that provide DI technology specifically for printer manufacturers. Representatives are Presstek and Creo.
V. 74 Karat74 Karat is a DI model that was developed by KBA in cooperation with Saige Angel in 1997 and launched in the market in 2000. It also uses DI technology from Presstek. The main feature is that the printer structure has been greatly improved. . Because the DI technology needs to be provided by other manufacturers and the price is expensive, it is applied to a larger-sized four-opening printing press, and the cost is even more unbearable. Therefore, 74 Karat adopts the structure shown in FIG. 3 . The arrangement of the rollers is an arrangement of five rollers, and the impression roller, the blanket cylinder, and the plate cylinder adopt a diameter ratio of 3:2:2. Two printing plates are installed on each plate cylinder, and two yellow and blue plates are mounted on the above plate cylinder as shown in the figure. Two magenta and black plate plates are installed on the lower plate cylinder. , so that two plate cylinders can achieve four-color printing. As with other machines, a DI imaging device is installed on each plate cylinder so that the four-color printer requires only two plate-making devices to complete the four-color printing plate, reducing machine costs.
74Karat still uses waterless offset technology, but its inking device uses short ink path anilox technology. The entire inking device consists of only one ink cartridge, a doctor blade, an anilox roller, and an ink fountain roller, making the ink adjustment reaction very sensitive, thus reducing the time required for print preparation. Although there is no ink zone adjustment function for performing local ink adjustment, since the temperature of the ink roller is strictly controlled, the ink film thickness on the printing plate can be guaranteed to be very accurate. However, since two printing plates are installed on each plate cylinder, the ink rollers need to perform frequent clutching when the printing plate is inked; the 3:2:2 diameter ratio also enables the transfer and transfer of the paper. Complicated, these are two layers of printing presses that can print on both sides of five colors, as shown in Figure 5.
The main performance parameters of the above DI printers can be clearly shown in Table 1.
In addition to these printers, other printer manufacturers such as Yoshiaki, Sakurai, Komori, and Roland also introduced their own DI printers, but their direct plate-making devices also use the products of Presstek and Creo. .
It should be noted that the DI printers described in this article are all mounted on the printing press and then plated and imaged, whether it is aluminum-based sheet printing or polyester printing. Whether it is manual or automatic loading, the working process is equivalent to transplanting the CTPlate device to the printing press. The information on the printing plate can only be memorized and not erased. Some DI printers use new imaging materials that have both memory and erase functions. The author will introduce them in other articles.
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