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Improve the stability of printing ink

at present, four-color offset printing machines have been very popular. Heidelberg, Manroland, gaobao and other well-known brand offset printing machines not only have excellent equipment performance and high degree of automation, but also are equipped with ink remote control system, which makes the control of printing ink convenient and reliable. However, in the actual printing process, it is not easy to stabilize the ink color of each batch of prints in other regions. In production, we often encounter quality problems caused by too large ink color differences, causing great losses to enterprises. The author has operated Heidelberg four-color offset printing machine for more than 10 years. Now I talk about some factors that affect the stability of ink color

1. Before printing, we should do a good job of pre adjustment based on experience

first of all, roughly adjust the ink amount of the ink bucket of each color group according to the proofing draft or the graphic area of the printing plate. This work is easier to complete on machines equipped with ink remote control system. It should be estimated that more than 80% of this should not be adjusted in a large range while printing, so as to avoid a large color difference caused by slightly poor gas resistance, gloss and transparency

secondly, according to the requirements of the production process sheet and the characteristics of the product, pre adjust all links such as Feida, paper receiving, ink performance, pressure and so on, so as to avoid being in a hurry during official printing. Among them, it is the most important to ensure the reliable, continuous and stable paper feeding of Feida. Experienced operators adjust the air blowing, air suction, presser foot, compression spring, paper pressing wheel, side gauge, front gauge, etc. in advance according to the width and thickness of the paper, straighten out the movement coordination relationship between various parts, ensure that Feida can feed paper smoothly, and avoid ink color differences caused by Feida beating. Here, it is suggested that experienced workers and masters can adjust Feida in advance

in addition, the viscosity, fluidity and dryness of the ink should be properly adjusted in advance according to the quality of the paper used and the size of the image and text area of the print, so as to improve the printability and ensure the normal printing. The ink color cannot be different due to frequent shutdown and cleaning of the paper wool and ink skin on the blanket and the printing plate. If you add all kinds of viscosity removers and inking oils in the middle of printing, the color deviation is certain

in a word, if we do a good job of pre adjustment before startup, we can greatly reduce the failure after the official printing, and the captain will have time and energy to focus on the ink color

2. Correctly adjust the pressure of water and ink roller

in the printing process, the graphic part of the printing plate must receive a continuous, uniform and appropriate amount of ink in order to obtain prints with consistent ink color. Therefore, the proper contact and rolling relationship must be maintained between the ink roller and the ink roller, and between the ink roller and the printing plate, so as to realize the good transmission of ink. If this work is not done carefully and correctly, the ink color will not be consistent. Therefore, each time when installing the water and ink rollers, we should adhere to the method of using the ink rolling bar to adjust the pressure between them one by one, instead of the traditional method of using the feeler gauge to test the tension, because the latter has a large actual error caused by various human factors, which should be banned on multicolor and high-speed machines. As for the width of the inking bar, it is generally 4 ~ 5mm. First adjust the pressure between the ink transfer roller and the inking roller, then adjust the pressure between the ink roller and the inking roller, the printing plate cylinder, and finally adjust the pressure between the water transfer roller, the plate water roller, the water transfer roller, the intermediate roller, and the pressure between the plate water roller and the printing plate cylinder. The ink bar between these waterways should be 6mm

after using the equipment for twoorthree months, it is necessary to readjust it, because the diameter of the ink roller will become smaller after a period of high-speed friction, especially in the transmission. The pressure between the inking rollers becomes smaller, and the ink accumulated on the inking rollers will not be transmitted. When Feida halts or stops to continue printing, due to the large amount of ink at this time, the positioning is inaccurate, and the ink color of the first dozens or even hundreds of inks is darker, so the ideal ink balance is difficult to achieve. This fault is generally not easy to find, and is only obvious when printing fine prints. In short, the operation of this aspect should be meticulous and scientific, otherwise it will cause the ink color of the mouth and trailing tip of water, ink bar and printing products to be different, which will artificially cause faults and increase the difficulty of operation

3. Achieve ink balance

as we all know, ink balance is an important content in offset printing. If the water is too large and the ink is too large, and the oil in water emulsification of the ink occurs, the print quality will certainly not be ideal. Through long-term practice, the author has explored some skills

first, ensure that the pressure relationship between water and ink rollers is properly adjusted, and the content of fountain solution and isopropanol meets the general standard. On this basis, start the machine, close the water and ink rollers, and then stop the machine to check the printing plate. It is better to have a slight dirt of about 3mm at the mouth of the printing plate. Taking the water volume at this time as the initial water volume of printing can ensure the normal printing of general graphic products and basically achieve the balance of water and ink

secondly, the water consumption should be flexibly adjusted according to other factors, such as the large graphic area of the printing plate, the rough surface of the paper, the need to add additives to the ink, and the change of printing speed, air temperature and humidity

in addition, the author also found that when the machine just started printing, the body temperature was low, and when the machine ran at high speed for oneortwo hours, the body temperature, especially the rubber roller temperature, would more than double, or even higher. At this time, the water consumption would gradually increase until the ink reached a new equilibrium state

it can be seen that it is not easy to achieve the balance of ink and wash, which requires operators to weigh and use dialectically. Otherwise, the ink stability is difficult to control, and high-quality prints cannot be printed

4. proofing correction and color sequence arrangement

in production, we often encounter such situations: the samples provided by customers are very non-standard, or only one color spray draft is provided without proofing. At this time, we should analyze the specific situation, and we can't use the method of hard increasing the ink volume or reducing the ink volume to pursue the effect of proofing. Even if it is close to the proofing draft at the beginning, the stability of the ink cannot be guaranteed, so the final quality of the print cannot be guaranteed. In this regard, the printing factory should actively exchange views with customers in a serious and responsible manner, point out the problems and modification suggestions of the sample, and make appropriate adjustments and reprints after obtaining consent

in production, the printing color sequence of multi-color machine is usually determined by ink viscosity. Because in multi-color printing, the ink is overprinted together by wet pressing, only by obtaining the best overprint rate, can we print stable and consistent ink. The arrangement of the printing color sequence must be subject to the characteristics and quality requirements of the printed matter, and cannot remain unchanged. At the same time, the viscosity of ink can also be adjusted. For example, the printing color sequence of a cover mainly in purple and a cover mainly in sky blue is different. The former is first green and then magenta, and the latter is first magenta and then green. Otherwise, the overprinted color will be spotted, which is neither plain nor stable. For example, for printing products mainly in black, black should be arranged in the last color group as far as possible, so that printing products with advanced technical capacity can have better gloss and avoid the occurrence of scratches and color mixing inside the machine

5. Cultivate good operating habits and strengthen work dedication

in doing any work, we must have a high heart and a strong sense of quality. We must standardize the process operation and adhere to the good traditional habits of "three evenings" and "three diligence". Take the example of frequently checking the sample. When comparing the signature on the template, the difference in distance, angle, light source, etc. will cause visual deviation, resulting in inconsistent ink color. At this time, the signature must be removed from the template and carefully compared; The long version of the printing plate needs to be baked to reduce the ink deviation caused by the version change; The blanket should be cleaned frequently, and more blotting paper should be placed after each cleaning to stabilize the ink color; After Feida finished printing, the ink color of the newly printed fiveorsix sheets is too deep to be drawn out. The printing speed should not be too fast. The important thing is to keep the machine stable and normal; When adding ink to the ink bucket, because the new ink is hard and has poor fluidity, it should be stirred a few times to avoid affecting the amount of ink, causing ink color deviation, etc

operators should constantly study, carefully observe and analyze, find out the factors that affect the change of ink color from all aspects, and take corresponding measures to properly prevent and overcome, strive to improve the stability and consistency of printing ink color, and effectively improve the quality of printing

reprinted from: printing industry

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