Small craftsmanship in flexo platemaking (I)

(Tools of the Trade) Friends of the flexographic printing industry, have you considered using an anilox roller without a "cell hole"? I am afraid that most people will say: "Impossible." As we all know, the anilox roller is the core part of the flexographic printing, it is to rely on the surface of the network to transfer ink. But at the same time, we also noticed that the printing plate used in flexographic printing has no cells, and that in the ink transfer system, the platen roller is next to the anilox roller. Since the anilox roller is covered with cells, in the same way, the field of the printing plate should also have a network of holes. These "print plate holes" may have an important influence on the future of flexographic printing. First, the smooth surface is immiscible with the liquid Long ago, people had discovered the fact that the adhesion of liquids to the surface of smooth objects was very poor. Such as water droplets on the windshield of a car, and "spattered milk droplets" on a glass tabletop, etc., are examples of fluids in our daily life that are incompatible with smooth surfaces. In the above two examples, the wetting action of the liquid on the smooth surface of the object is very uneven, but in a spherical or random pattern. Two more examples are closer to our industry, such as the printing plates used in offset printing. We know that in offset printing, plates must first be plated in order to evenly wet the fountain solution. Edition to avoid the above problem. Similarly, a number of pockets are engraved on the surface of a gravure printing gravure cylinder, and these cells can store and transfer ink during operation of the machine. The surface of the photopolymer printing plate is originally very smooth, and is also non-porous, but on such a surface, it is impossible for the ink to spread uniformly. To print a flat field, you must use more ink, and the required printing pressure is slightly larger than the normal pressure. In the flexographic printing process, too much ink and excessive printing pressure is exactly The root cause of most printing failures. If the cell site is also used in the field part of the plate, the need for ink volume and printing pressure can be greatly reduced, that is, there is no need for a large amount of ink and excessive printing pressure, thereby helping to improve the printed matter. the quality of. Second, on the field of regional screening In flexographic printing, in order to solve the problem of smooth surface of the flexographic, one of the methods is to screen the field. This method has been used in the flexographic printing industry for at least 15 years, and has also achieved varying degrees of success. In fact, the fundamental task is to determine the best dot shape, the best cable angle, and the best number of screen lines in the field, so as to improve the shape of the printing plate. The results of the first phase test show that although the size of the best network is generally expressed as a percentage value (for example, 96% of screen dots with 133 lines/inch screen), the actual size of the non-network area (usually "Micrometer" is more important. For the sake of brevity, we will refer to the non-dot area on the printing plate as the "printing plate hole." For example, 96% of the dot area corresponds to 4% of the cell (100-96=4). Assuming that the number of screen printing lines is 133 lines/inch, the diameter of this 4% network hole is 43 microns. The enlightenment of these tests is that in flexo printing, it is not the “percentage value” (such as 4%) but the “micron diameter” (such as 43 microns) that is decisive for the transfer of ink. Assume that the number of screens is 133 lines/inch, and the number of lines of the anilox used is 800 lines/inch. Take 96% of the screen as an example. If 43 microns is the optimal size of the cells, the following problems will arise: : Why use 1/133 inch intervals to separate the cyberspace? Why not separate them without 1/800 inch intervals? Why do they cover only 4% of the surface of the plate? Why not cover 40% or more of the surface of the plate? We studied the optimal number of screens for ink transfer. Through research, we have found that the number of screens in the field is actually the same as the number of screens in the anilox roller. However, the non-dot (ground) area can take special shapes. For example, the circular dot used in the solid area is actually a transformed diamond dot. In the high frequency area, this circular dot is very small and many There is no imaging on the plate, and even if it can be imaged on some plates, it seems to be insignificant. This effect is especially noticeable when using 16-bit or higher number of screens. If we expand the number of network points, it will bring a series of problems, just as the connection of outlets forms a channel, which often hinders the normal operation of the network. Third, the formation of "printing plate hole" on the plate Through the exposure machine or CTP equipment exposure imaging, you can get in the plate in the field area to get a cell site. The user generally selects the shape of the cell in combination with other characteristics of the job. The RIP software informs the output device what kind of cells should be formed in the field, while forming normal halftones in other parts of the same tone. The shape of the plate cavity is displayed as a positive 1-bit TIFF image that can output film or digital plates on any imaging device. In the process of copying, from the digital file to the film and to the printing plate, the cell site constantly shifts. Since the cells in these high frequency areas consist of a few pixels, the best results can be obtained if the imagesetter has been calibrated for the flexographic printing process. The density is higher and the edges are clearer. When a film is output on an imagesetter that has been calibrated for a flexographic printing process, the reduction in the number of dots in the dots will correspondingly increase. In fact, the cells that are formed on the plate by the exposure plate will be reduced, and the expansion of the cells when the film is output can precisely compensate for this. Many users choose to add screens in all field areas. In addition, screens and lines can also be screened. The advantages of screening the field area or the fine text and lines are as follows: 1. The field area has a higher density value. 2. The field area looks smoother. 3, reduce or eliminate the "glow." 4, the image is clearer and sharper. 5, Yin map (text) paste is even lower. Fourth, the field area has a higher density and smoother. After the screen is added to the field, the printing plate has a more adequate amount of ink, so the field area obtained is higher in density than the non-screened plate, and is evener. Practice has proved that this is indeed the case when the amount of ink is low (such as when printing halftone images) or when the amount of ink is very high (such as when printing negative lines or intaglio). V. Eliminating Halo Practice has proved that if the actual area of ​​the printing plate or fine text and lines are screened, the halo in the flexographic printing can be effectively reduced or even eliminated. Sixth, the Yang Wen is clearer, Yin Wenwen is not sticky to the field area or the fine text and the line partial after screening, the Yang Wen which prints out is clearer, the Yin Wen does not stick to die. Print the same image with the screened and non-screened plates. Observe the results carefully and compare the overwhelming death of the two images with the expansion of the positive text. You will find that: Under the high magnification magnifying glass observation can still find some shortcomings and deficiencies, but within the normal observation distance, the former print out the graphic effect is significantly better than the latter. Seventh, saving ink There is another advantage to be pointed out, this is to reduce the consumption of ink. The user's practice has already confirmed this. In other words, when printing solid areas or fine text and line parts after screen printing on solid areas or fine text and lines, the printer can use a web with a lower ink transfer rate (ie, a higher number of screen lines). Roller, therefore, the amount of ink used to "cover" the substrate material is also less. Below we analyze from a purely digital perspective. If one anilox roll with 4 million cubic centimeters of ink is replaced with an anilox roll with 3 million cubic centimeters of ink, the amount of ink transferred will be reduced by 25% and actually transferred to the substrate material. The amount of ink (that is, the amount of ink eventually consumed) may be less. So far, there are no clear statistics on the issue of ink saving. From a business survey, this amount is still quite large. If the user's ink consumption is US$1 million, a 1% decrease in the amount of ink transferred means that US$10,000 can be saved each year; a 10% reduction in the amount of ink delivered means a savings of US$100,000. This shows that the potential for cost savings is still very large, and researchers will continue to conduct in-depth research in order to obtain more detailed information.