Gravure Printing Points Features and New Technologies
Dots are the basis for realizing the level of image tonal adjustment. Different printing methods have different effects on the transmission of dots. Since dots in gravure printing and flexo printing are more severe than offset printing, the effect on image tonality is even greater. In the transmission process of the dot, the dot shape is an important factor that affects the reproduction of the image tone, especially at the printing stage. The traditional dot shapes are square dots and circular dots. There are also chain points (or diamond dots), letter points, composite points, frequency conversion points, and frequency modulation points. At the same percentage of outlets, the shape of different outlets has a different sum of their perimeters, and the increase in outlets is also different. When the dot increases, it expands outward along its edge, so the larger the perimeter, the more serious the dot increases. In addition, in the process of small and large dots, there are always sites where the dots overlap, and the density will suddenly increase due to overlapping. As a result, the continuity of the tone curve is destroyed, resulting in the loss of certain levels of tone areas. For example, skin tones, midtones that are just in the yellow and magenta versions, can easily cause stiffening of the tone and lack of subtle changes. In the reproduction of skin tone, the chain point is better than the circle point and the square point because the overlap of the mesh point avoids the midtones, and the overlap of the mesh points is divided into two times, and the jump caused by each time is weakened. The tone jump caused by the lap of the network can also be overcome by adjusting the parameters of the RIP in principle, but it has a certain degree of difficulty. The first is that the amplitude of the jump has a lot of factors, and it is random within a certain range, even if Careful presupposition, it is still difficult to offset all the defects; the second is that the position of the jump can only give a range, it is difficult to accurately locate. Therefore, the gradation jump caused by the overlapping of outlets can hardly be eliminated in actual production, and can only be mitigated by the cooperation of the dot shape and the characteristics of the produced image.
The gravure nets are composed of net walls and net holes, which are different from other print nets such as letterpress, lithography, and the like. Relief and lithography express the level of print with the size of the dot area, while gravure expresses the level with the concave part of the gravure (ink mesh). The gravure nets need to have a net wall to support the squeegee and to enhance the adsorption force of the net on the ink. The intaglio concave part can be divided into different parts of the concave part with different surface areas according to the shape; the depth of the concave part is equal to the surface area; the depth and surface area of ​​the concave part are not equal to 3 kinds. Compared to other printing plates, these gravure printing plates that have been fully used today are very complicated to produce. The color separation film (original) used in gravure production also has a complicated and difficult manufacturing process. In the gravure platemaking process, although the range of dots is compressed a lot, because of the thick ink layer during printing, the color of a gravure printing product is usually more saturated and more vivid than the color of an offset printing product. Due to the special nature of gravure printing dots, the increasing rule is also quite different from that of offset printing. The hue of the used ink is also very different from ordinary offset printing ink. Therefore, the level curve and gray balance curve used in gravure platemaking are different from those of offset printing. Electric extensions and most scanners are preset for offset printing and have a set of tonal adjustment curves. At the time of plate making, only the preset curve needs to be converted into plastic and concave. At present, plate-making manufacturers usually perform offset conversion during image processing, and inconveniently handle the color levels defined in the graphic portion. The ideal way is to automatically do the gum-convex transformation in the computer where the RIP processes the graphic-text layout description file, so that most of the adjustments can be done automatically in the RIP, and the special adjustment in the image processing is only as an auxiliary means. In addition, in gravure printing plates, it is sometimes necessary to use different dots and different numbers of screen lines in different parts of the same layout. Most elements do dot compression and some elements do not do dot compression. Some of these requirements can be solved by existing software, and some can only be achieved by enhancing the functionality of RIP and design software.
The gravure printing screen has a very high demand for the dot shape. In modern electrical extension screens, gravure digital dot systems are stored, such as white cross dot nets, honeycomb hexagonal dot nets and other special shape dot nets. The electronic color separation of the image can be flexibly adjusted and the data can be accurately recorded. Intaglio dot images can be directly recorded. In ESK, a complete solution designed for gravure plate prepress processing, ESK's unique gravure dot technology is available. It consists of a compression dot-reduction tool, a special gravure dot, dot application tool, and a quick proof print tool. And color management tools. After the application of production and further research, ESK has achieved new technical improvements. At present, ESK network point technology mainly includes the following points.
(1) Cell site. The network point is from 0 to 60 degrees of screen angle range, and the network angle is 15 degrees to avoid collision, so it is easy to get 4 available angles without collision. The traditional method can have three angles not hitting the net for the main color version, usually the fourth color version is the weak color version, and when the three main color versions are superimposed together, there will be slight collisions. Gravure printing is usually preceded by a white base plate. In some cases, the white base plate will crash into other color plates, and white spots will be made from honeycomb spots, which will reduce the chance of collision. To sum up, the honeycomb structure network points have a hexagonal field in the field when the loss of printing and corrosion is smaller than the square network dots; the resistance to printing force is strong; under the same printing difficulty, the honeycomb structure network points can achieve larger network points. Density, i.e., the printing line number of printing lines is 200 lines/inch, the printing difficulty with the honeycomb structure dots 7 is comparable to that of the image lines printed on the permanent orthogonal grid dots of 175 lines/inch. Because in 50% of the flat screen, the size of the outlets is equivalent to the spacing between the outlets; when the cellular network outlets are overlaid in a multi-colored version, the chance of collision is small. The hierarchical structure of the honeycomb structure, the shape and arrangement of the outlets are all relatively good, and it is a relatively promising outlet.
(2) T-shaped outlets. Also known as the gravure square dot of communication. The network can increase the leveling of the ink in the field, reduce the ripple phenomenon, and make the field printing even and full. Nippon Shinco also uses similar outlets in its laser direct plate making system, which has achieved remarkable success in production. ESK software also uses this function, so users can apply a similar Japanese Shinco company to the coating corrosion process. The technology developed by its filmless laser platemaking system. In practice, we have found that the requirements of T-junctions on the process must be justified by the depth of corrosion and the width of ink communication.
(3) Chain outlets. Its shape and arrangement are closest to those of the electric engraving machine. The width of the chain point is adjustable, which is similar to the adjustment of the axial step of the electric engraving machine. This adjustment can be independent of the radial step. This network provides a new tool for the success of the etching method to draw on the gravure process. In the early process of the etching method, the laser photographing machine outputs the film. There are many methods for adjusting the shape and arrangement of the dots in the technique, and the level curve is also relatively easy to adjust.
(4) frequency conversion network. Mainly used for high-line offset printing. For example, when 330 lines/inch images are printed with offset printing, the dots in the high-light part are too small (the dark tone is also very little in the white space), which is difficult to achieve in the process. HMS solves this problem by using the baseline in highlights and shadows. Based on this idea, we designed a frequency conversion network for gravure printing. The application of frequency conversion dots in gravure printing is not mainly to solve the problem of high-line number printing. It is suitable for improving the quality of front plane and highlight areas. From the usual 175 lines/inch condition. Below 10% of the outlets are very unstable in terms of process. It should not be easy to evenly spread the front level screen, and it is difficult to reproduce the high-level level steadily. Although the 150 lines/inch or 133 lines/inch image is better at the shallow tone level, the middle portion of the layout's main body appears to be too thick. The application of frequency conversion dots in gravure printing is much more complicated than offset printing. It is necessary to adjust the frequency range of the inverter (for example, 1% to 12% for the frequency conversion range) and the size of the starting point for the production process. However, it also has a negative effect, such as small dirty spots will be clearly shown; a gradient of high-light part will appear a ladder, but has little effect on the image, there are still visible steps in the large area of ​​the gradient. Therefore, it is still necessary to decide whether to use it according to the characteristics of the layout.
(5) Star outlets. In the field, outlets can reduce the area of ​​the net wall between the ink caverns. Without reducing the strength of the net wall, the outlets increase the dot area, so the ink content is relatively large, which has certain benefits for printing in the field.
(6) Hierarchy outlets. The shape of traditional gravure dots is the same from high light to solid. This is a simplified approach. In fact, the dots in the hierarchy are the best solutions. However, the amount of ink in the dots in the field is not as large as other dots. It is not easy to make it flat. Therefore, we have designed hierarchical meshes that combine dots with other gravure dots. This kind of hierarchical network is easier to make in the highlights of small points. Middle tone to the high-profile and low-key levels are also more smooth.