Laser ablation plateless waterless offset printing technology

Waterless offset printing is a hot topic discussed in the printing industry in the past 10 years. Waterless offset printing has been one of the most attractive topics ever since the beginning of 1994 in every print community gathering abroad. There are also many articles introducing this printing method. Domestic seminars have also been held in this area. Some people have a positive attitude toward waterless offset printing, and others hold skepticism and wait-and-see attitudes. People with a positive attitude think that this printing method has high printing quality and no environmental pollution; skeptics believe that this printing method is too harsh on the environmental conditions of the printing industry. The plates and inks used are special and the price is too expensive, from quality and In terms of price ratios, it does not have any obvious advantages over ordinary offset printing. This situation has made the development of traditional waterless offset printing technology slow over the years. Since 1996, we have conducted research on computer direct imaging plate-making technology and related materials. This is a project of direct computer-to-plate and direct printing. In this project, we adopted laser ablation of computer-controlled waterless offset printing. At present, laboratory research has been completed and a laser-ablated type waterless offset printing plate has been developed, and an ink and a laser ablation direct plate making experimental machine have been developed. We used the self-developed platemaking system to make plates on the plates we developed, and we used waterless offset printing inks we developed to carry out waterless offset experiments on ordinary printing presses. We achieved satisfactory results. Below, combined with our research, talk about the basic characteristics of laser ablation plateless offset printing technology and related materials. Laser ablation plateless waterless offset printing technology is a kind of waterless offset printing technology used in computer direct plate making and computer direct imaging printing. It has been used on Heidelberg QM DI-46 printing machine. The traditional waterless offset platemaking process and the water offset process are the same. The only difference is that the development and fixing processes are different after the printing process. The former is to remove the non-graphic part of the PS plate by developing and fixing, leaving the graphic part to form a plano-convex plate; and the latter is to remove the surface ink-repelling layer of the corresponding area of ​​the picture and text by the action of liquid medicine to form a plano-gravure. In this sense, ordinary waterless offset printing and ordinary water offset printing are the same system in the process flow of plate making. Laser ablation plateless waterless offset printing is the computer-controlled laser beam to transfer the computer-edited graphics directly to the waterless offset printing plate. After washing the dust generated in the platemaking process, the printing plate is ready for printing. The prepared version is Flat intaglio. Compared with the former two, it is clear that this plate making process has been greatly simplified compared with the former two, and it belongs to the direct computer plate making. Therefore, it is a new technology that is different from traditional offset printing and waterless offset printing, and it constitutes a plate printing system and material system. Its advantage lies in its advantages of both digital platemaking and waterless offset printing. The future of new printing methods. First, laser ablation waterless offset plate This plate consists of three layers, its structure and imaging principle shown in Figure 1. The plate base is a plastic sheet or metal plate with ink absorbing properties, and the middle layer is an imaging layer. It has a high absorption rate for the laser and is easily vaporized by the laser. The surface is an ink repellent layer with high smoothness and low surface energy. Not sticky when printing. The plate-making method uses a laser ablation system controlled by RIP to edit computer-edited graphics and utilizes laser ablation to transfer the images to the plate (Fig. 1). The powder produced in the plate making process is removed in an appropriate manner and the printing plate is ready to be printed by hanging it on the printing machine. In the printing process, the graphic part is sticky and the non-graphic part is not sticky, so that waterless offset printing is achieved. Fig.1 Structure of laser ablation type plate (a) and imaging principle diagram (b) The main performance indexes of this plate are as follows. 1. Plate resolution and laser power requirements Resolution and laser power required for plate making are determined by measuring the line width of the laser beam ablated on the plate and using its width to characterize the resolution. The test results of a plastic-based plate are shown in Figure 2. As can be seen from Figure 2, when the laser power is small, the width of the ablation line is narrow, and its width becomes wider as the laser power increases. When the laser power increases to a certain value, the width of the ablation line no longer varies with the laser power. , that is, reaching a stable area. We call this transition point "inflection point." It can be seen from Figure 2 that if the quality of the plate is stable and the laser emission is stable, the plate-making accuracy can be adjusted by adjusting the laser power with the light path unchanged. Because the linear relationship between the resolution of the plate and the laser power changes before reaching the inflection point. The plate resolution of the two plate samples shown in FIG. 2 is about 1200-2500 dpi, and the corresponding light power is 3-4 watts. When the power is greater than the power corresponding to the point, the resolution reaches a stable value, ie it does not change with the power change. Fig.2 The relationship between resolution and laser power of laser ablated waterless offset printing plateFig.3 Curve of value of Tack for waterless offset ink (left) and normal offset ink (right)2. The surface energy of the ink repellent layer is a key indicator of this type of plate. If the surface energy is not low enough, waterless offset printing is difficult to achieve. We actually measured the surface energy of the developed plate. The results are shown in Table 1. In Table 1, γ is the surface energy, and γp and γd are polarization energy components and dispersive energy components of the surface energy, respectively. Experiments have shown that the plate 1 can be waterlessly printed with waterless offset inks, while the plate 11 is not capable of waterless offset printing because the plates are sticky. This indicates that the surface energy of the waterless offset plate also has a threshold area. When the surface energy is greater than this area, waterless offset printing cannot be achieved. In the case of the waterless offset ink we use, this threshold is between joule meters. Table 1 laser ablation type waterless offset plate surface energy (10-3 Joules / m 2) plate type surface energy γ polarization energy γp dispersion energy γd plate 124.70.124.6 plate 1128.4028. 4 Table 2 Ordinary offset inks, waterless offset inks Adhesion and Viscosity Measured values ​​Ink type Adhesion Initial /300s/25°C Viscosity / PAS/25°C Waterless offset printing effect Ordinary offset printing ink 128/1463.8 Cannot print its own development Waterless offset printing ink 92/7611.4 Good Table 3 Under the same printing conditions, different printing pressure when the printing spot expansion conditions Edition pressure (file) printing pressure (file) to the ink version of the printing spot diameter d1 printed on the corresponding printing Spot diameter d2A = d2 / d1 (%) 511 Small 342 μm 318 μm 93.0551 Small 342 μm 320 μm q93.65101 Small 342 μm 326 μm 95.3 Table 4 Under the same printing pressure conditions, different printing pressure when printing spots to expand the situation Press (file) Printing pressure (file) to Ink plate on the print spot diameter d1 printed on the corresponding print spot diameter d2A = d2 / d1 (%) 151 small 342 μm 322 μm 94.1551 small 342 μm 320 μm 93.6101 1 342 μm 335 μm 98.0 3. The resistance to print force is an important indicator. Printing experiments show that the printing material of this type is between 15,000 and 20,000 impressions. The resistance of foreign similar products is generally about 20,000 India. two. Matching ink and its characteristics This is one of the main materials that make up waterless offset printing. According to Hagenbach Poiseuille's law, the ink's viscosity, tackiness, and its variation over time are key indicators for waterless offset inks. We actually measured the adhesive viscosity and its change with time of waterless offset printing inks and ordinary offset printings studied in this laboratory. The results are shown in Table 2 and Figure 3. In Table 2, "initial/300s/25°C" refers to the viscosity at the beginning of the test and after 300 seconds, and the test condition is 25°C. It can be seen from Table 2 that to meet waterless offset printing, the required ink must have low tackiness in the same viscosity. The curve on the left in FIG. 3 is the Tack curve of a waterless offset ink; the curve on the right is the Tack curve of a normal offset ink. In FIG. 3, the abscissa indicates ink stickiness, and the ordinate indicates action time. From Figure 3, it can be clearly seen that: (1) waterless offset inks have low adhesiveness, about 70, while ordinary offset inks are about 170; (2) waterless offset inks do not substantially change with time, ie they are very stable However, the offset of conventional offset inks varies with time, ie instability. From the above test results, it can be seen that the main requirement of the printing ink for waterless offset printing is low adhesion and stability. Third, the plate-making equipment The plate-making equipment of this plate is similar to the laser image-setter. It consists of an electronic prepress system, RIP, interface system, laser system and electromechanical components. The difference with a laser imagesetter is that the laser used in this platemaking device is a high-power infrared laser, which can be a semiconductor laser or a YAG laser. We used a YAG laser in our experiment. The relationship between platemaking precision and laser and related equipment parameters can be designed and described by a system agenda group. We designed and manufactured a drum platemaking system and a flatbed plate making experiment machine, respectively. Both of them can realize computer laser ablation and direct plate making. The machine can be operated under bright room conditions. The process is simple and easy to operate. IV. Printing Experiments and Conclusions We used the self-developed laser ablation direct platemaking system (including drum type and flat table type), plates and inks for plate making and printing experiments. The results are described below. Plate making: The method is simple. After the laser ablation, only the dust in the plate making process can be washed with syrup or water to obtain the printing plate. Printing: Hanging a good version can start printing. After starting the machine, about four or five sheets of paper can be used to print a sample. No water is used in the printing process, and there is no need to deal with ink and ink balance. Plate material resistant to India: 15,000 to 20,000 printed. Ink: By measuring the density of printing spots and the density of non-graphical portions, it can be seen that the printed images are clear, and the non-graphical portions are not bottomed ash, indicating that both the plate and the ink are available. Printing temperature: A long-term printing experiment was conducted from 18°C ​​to 23°C. No change was found in the printing effect. This indicates that the printing is not too demanding for the printing environment. In particular, when the printing speed is not too fast, there is no problem. Printing effect: We measured the dot changes under different printing pressure and pressure conditions. The results are shown in Table 3 and Table 4. In Table 3 and Table 4, the unit meanings listed in "Printing Pressure", "Printing Pressure" and "Ink Supply Volume" refer to the number of scales given on the printing press. The amount of ink given in the two tables is a suitable amount in this experiment. From the experimental data given in Tables 3 and 4, it can be inferred that this type of printing is less prone to dot gain problems. The printed dots are 1% to 5% smaller than the information dots on the plate, and are larger. Within the range of printing parameters change, the printing dot size changes very little, that is, the printing effect is stable. Through the research and practice of this topic, we have the following understanding of the waterless offset printing plate made by laser ablation: Laser ablation waterless offset printing is a new type of waterless offset printing technology. It not only retains the advantages of waterless offset printing, but also has the advantages of simple plate making process and can be used in computer direct plate making and computer direct printing. This is a form of printing that has characteristics, its own existence and development space and good prospects. 2. In the near future, this method of plate-making has obvious quality and technical advantages in short-format small-format printing. The main reason constraining its development is that plates and inks are too expensive. If the price of plates and inks can be reduced to be comparable to that of ordinary PS plates and offset inks, and the price of plate-making equipment can be comparable to or lower than that of laser imagesetters, such plate-making methods and printing will surely develop. From our research results, this possibility exists. 3. This type of plate making has advantages in the direct printing of computers, and this advantage has been proved by the QM DI-46 presses in Heidelberg. The goal of our research work is also to use this technology for direct computer printing.