Learn about commercial rotary printing color control
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Many printing documents of current printing companies are foreign electronic documents. Printing companies only need to output printing plates according to foreign electronic files, and then print them on the machine. However, most of the foreign electronic files are designed and produced by the advertising company. They don't know much about the printing process and mode. The pictures are mostly set in RGB and Lab mode. The computer monitors are not color management, and soft proofing cannot be achieved. When printing companies directly use such foreign electronic files for typesetting printing, it is very difficult to use commercial rotary printing machines to chase colors. The printing effect is quite different from that of digital samples, and the overall color is smeared and lacks layering. This article takes the author's Beiren Fuji BF4110B commercial rotary press as an example to analyze how to ensure the color accuracy when using foreign electronic files from the following aspects.
Graphic processing
First, convert the color mode of the foreign electronic file to CMYK mode on Photoshop software, and use the eyedropper tool to view the color of the graphic to determine the main color composition of the file. Since the number of ink rollers of Beiren Fuji BF4110B is relatively small compared with that of Heidelberg commercial rotary printing press, there is a certain gap in the uniform ink performance, which tends to cause the ink roller ink layer to be thicker, and the ink roller is evenly inked on the opposite sides of the ink roller. It is not enough, and because the commercial rotary printing machine uses continuous paper feeding to print, the paper is stretched under the tension, and it is easy to appear obvious dot gain, so the finished product will be obviously dim in the dark and bright tone. The effect is to reduce the dot value appropriately during the mapping process.
1. Bright part
For example, blue sky, white clouds and other graphic texts need to reduce the values of M and Y to avoid smudging during printing.
2. Dark adjustment parts
For example, green forests are mostly overprinted with CMYK four colors. It is necessary to reduce the values of K and M to avoid darkening of the darkness during printing, resulting in black and unclear prints and no layering.
3. Large area flat net
When using a commercial rotary printing machine for printing, the large-area flat net dot increase phenomenon is obvious, so it can be appropriately increased according to the actual situation, and the maximum value is not more than 40%.
Printing unit adjustment
1. Reasonably adjust the printing machine ink roller, plate cylinder, blanket cylinder pressure
The pressure between the plate cylinder and the blanket cylinder is controlled to be 0.15 to 0.20 mm, and the two ink rollers are parallel to the plate cylinder, and the embossing width between the plate roller and the plate cylinder is 4.0 to 5.0 mm. .
2. Reasonably control the concentration of dampening solution and the amount of water supply
Control of the concentration of dampening solution plays a crucial role in ink balance and print quality. If the concentration of the dampening solution is low, the ink around the dot can not be removed, which will cause the dot to increase, and the paste will cause the paste; if the concentration of the dampening solution is too high, the printing force of the PS plate will decrease and the ink will be emulsified too fast. . When printing with Beiren Fuji BF4110B, the pH should be controlled at 4.0 to 4.8.
(1) When the printed paper is loose or the paper powder is too large, due to the high viscosity of the printing ink, the paper and paper powder often accumulate on the blanket in the embossing, which will increase the friction of the printing plate and make the printing plate dirty. . In this case, the dampening solution concentration should be appropriately increased; and when printing a tough and white paper, especially for coated paper and thermal paper, the dampening solution concentration should be appropriately lowered.
(2) The layout of printed matter is varied, both in the field and in lines and dots. If the layout is mostly based on lines and solid words, because the ink area is small, the concentration of dampening solution should be adjusted appropriately, so that the blank layout is not easy to get dirty; if the entire plate layout is a dot structure, it should be used. Low-concentration dampening solution; for printing plates coexisting in the field and in the dot, a multi-faceted principle should be adopted to ensure the quality of the printed product is stable.
Phototype, plate control
Pre-press output requires reasonable control of exposure time and developer concentration, so that the printed plates are clear and the dots are firm, which not only ensures the transfer effect of the dots, but also has a high printing durability. Through experiments, it is found that in the printing process, compared with the elliptical, diamond-shaped, and square circular dots, the pure circular dot is less deformed by the tension (pressure) force, but tensile deformation and dot enlargement still occur. . Therefore, in the previous graphic processing, the following aspects need to be controlled.
(1) Adjust the photo-reverse compensation curve to reduce the dot below 5% by 2%, 90% by 5%, and the exposure time to 100-120s.
(2) The PS plate with better quality is used to ensure that the blank part of the printing plate has good hydrophilic and oil repellency, and the oil and water repellency of the graphic part is good.
(3) In order to achieve an ideal development effect, it is preferable to use a developer solution compatible with the PS plate. Because the PS plate produced by different manufacturers has strong and weak alkali resistance, if the anti-alkaline PS plate is developed with a strong alkaline developer, the photosensitive layer without photodecomposition will be seriously affected, resulting in a smaller dot after development. The image tone is lost, so it is best to use the developer in the concentration range specified by the manufacturer. Otherwise, when the developer concentration is too large, the development operation is not easy to control due to the development speed too fast, especially the image portion. Increased in sex, it is easy to cause the dot to shrink, damage, brighten the small dot loss or the coating is thinned, which causes the printing plate to reduce the printing durability; when the developer concentration is low, the alkali is weak, the development speed is slow, easy There is a phenomenon that the development is not clean, the layout is dirty, and the small dots are dark.
Due to the fast printing speed of the commercial rotary printing press, the color control is difficult, and the technical requirements of the operator are high, the preparation work before printing is crucial, on the one hand, the adjustment time can be shortened, the consumption is reduced, and the production efficiency is improved; Guarantee product quality, improve customer satisfaction, and make enterprises have an advantage in market competition.