If you have any needs pls contact me-
Whatsapp number of Ivy: +86 18933516049 (My Wechat +86 18933510459)
Email me: 01@songhongpaper.com
Currently, four-color offset printing machines have become very popular. Brands such as Heidelberg, Manroland, and Gobo, among others, not only have excellent equipment performance and high automation levels, but also are all equipped with ink color remote control systems, making it convenient and reliable to control the ink color of the printed products. However, in actual printing processes, achieving stable ink color for each batch of printed products is not an easy task. During production, quality problems caused by significant ink color differences are often encountered, causing great losses to enterprises. I have been operating an Heidelberg four-color offset printing machine for over 10 years. Now, I would like to share my understanding of some factors affecting the stability of ink color.
1. Before starting the printing, do a pre-adjustment based on experience.
Firstly, based on the graphic area of the sample or printing plate, roughly adjust the ink supply volume of each color group of the ink rollers. On machines equipped with a color control system, this task is easier to accomplish. There should be an 80% estimation for this. Do not adjust the ink volume on a large scale while printing; doing so may cause significant color differences.
Secondly, in accordance with the requirements of the production process sheet and the characteristics of the product, the various links such as the feeder, paper collection, ink performance, pressure size, etc. should be adjusted in advance to avoid confusion during the actual printing. Among them, ensuring the reliable, continuous and stable paper feeding by the feeder is the most important. Experienced operators usually first adjust the blowing, suction, press foot, pressure spring, paper press wheel, side guide, and front guide according to the size and thickness of the paper, and then adjust the movement coordination relationship among all components to ensure smooth paper feeding by the feeder and avoid uneven ink color due to the interruption of the feeder. It is suggested that experienced workers can make pre-adjustments to the feeder.
In addition, before printing, the viscosity, fluidity and drying properties of the ink should be appropriately adjusted according to the quality of the paper used for this print, as well as the size of the graphics and text areas. This is to improve the printing adaptability and ensure that the printing process proceeds normally. It is essential not to cause inconsistent ink color due to frequent machine stops for cleaning the rubber blanket and printing plates of paper fibers and ink skins. If various desiccants and color-matching oils are added halfway through the printing process, color deviations will definitely occur.
In conclusion, if the pre-adjustment work before starting the machine is done properly, it can significantly reduce the number of faults that occur after the actual printing begins. Also, the machine operator will have the time and energy to focus on controlling the ink color.
2. Properly adjust the pressure of the water and ink rollers
During the printing process, the graphic part of the printing plate must receive continuous, uniform and appropriate ink to obtain consistent ink color on the printed product. Therefore, the ink rollers must maintain an appropriate contact and rolling relationship with each other to achieve a good ink transfer. If this task is not done carefully and correctly, the ink color will not remain consistent. Therefore, when installing the water and ink rollers each time, the method of using ink rollers to adjust the pressure one by one is always adopted, instead of the traditional method of using a feeler gauge to test the pulling force, because the latter has a large actual error due to various human factors, and it should be prohibited on multi-color and high-speed machines. As for the width of the ink rollers, generally 4 to 5 mm is appropriate. First, adjust the pressure between the ink transfer roller and the serial ink roller, then adjust the pressure between the ink roller and the serial ink roller and the printing plate roller, and finally adjust the pressure between the ink supply roller, the counter-plate water roller, the serial water roller, the intermediate roller, and the pressure between the counter-plate water roller and the printing plate roller. The pressure between the counter-plate water roller and the printing plate roller is also 6 mm.
After the equipment has been in use for two to three months, it needs to be re-adjusted. This is because the diameter of the ink rollers will decrease after a period of high-speed friction, especially more pronounced in the transmission process. The pressure between the ink rollers has decreased, and if the ink accumulates on the ink rollers, it will not be able to be transferred. When the feeder stops or restarts printing, due to the large ink supply at this time, the ink color of the first several dozen or even several hundred sheets will be darker than the ideal balance of ink and water. It is difficult to achieve the ideal ink-water balance. This fault is generally not easy to detect, and it becomes more obvious when printing on finer products. In summary, the operation in this aspect should be meticulous and the methods should be scientific. Otherwise, it will cause the ink and water marks to be uneven in the leading and trailing edges of the printed products, artificially causing the fault and increasing the operational difficulty.
3. Achieve a balance of ink and water
It is well known that ink-water balance is an important aspect in offset printing. If there is too much water and too much ink, causing the ink to undergo emulsification in an oil-in-water manner, the quality of the printed product will naturally not be satisfactory. Through long-term practice, the author has discovered some techniques.
Firstly, ensure that the pressure relationship between the water and the ink roller is properly adjusted, and that the content of the dampening solution and isopropyl alcohol conforms to the general standards. Based on this, start the machine, close the water and ink rollers, then stop the machine and check the printing plate. It is preferable that there is a slight 3mm of dirtiness at the edge of the plate. Use the water volume at this time as the initial water volume for printing, which can ensure the normal printing of general graphic products and basically achieve the balance of ink and water.
Secondly, the water consumption should be adjusted flexibly based on other factors, such as when the graphic area on the printing plate is large, the surface of the paper is rough, additives need to be added to the ink, or when the printing speed, air temperature and humidity change.
Furthermore, the author also discovered that when the machine was just turned on for printing, the body temperature was relatively low. However, after the machine had been running at high speed for one or two hours, the body temperature, especially that of the rubber rollers, would increase by more than double, and even higher. At this point, the water usage would need to gradually increase until the ink and water reached a new equilibrium state.
It can be seen that achieving a balance of ink and water is not an easy task. Operators need to make multiple considerations and apply the principles dialectically. Otherwise, the stability of ink color will be difficult to control, and high-quality prints cannot be produced.
4. Correction of the proof and arrangement of color sequence
In production, such situations often occur: the sample provided by the client is not standard, or no sample is made but only a color print is provided. In such cases, a case-by-case analysis should be conducted. One cannot simply increase or decrease the ink quantity to improve the effect of the sample. Even if it initially gets close to the sample, it cannot guarantee the stability of the ink color, and thus cannot ensure the final quality of the printed product. Therefore, the printing factory should adopt a serious and responsible attitude to actively communicate with the client, point out the problems in the sample and the modification suggestions, and only after obtaining the client's consent can appropriate adjustments be made before reprinting.
In production, the printing color sequence of a multi-color machine is usually determined by the viscosity of the ink. Since in multi-color printing, the inks are overlaid in a wet-on-wet manner, only when the best overlay rate is achieved can a stable and consistent printed product be produced. The arrangement of the printing color sequence must comply with the characteristics and quality requirements of the printed product, and cannot remain unchanged. At the same time, the viscosity of the ink can also be adjusted. For example, for a cover with a predominance of purple and one with a predominance of sky blue, the printing color sequence is different. For the former, cyan is printed first followed by magenta; for the latter, magenta is printed first followed by cyan. Otherwise, the printed colors will appear as spots, neither uniform nor stable. For printed products with black as the dominant color, black should be arranged in the last color group. In this way, the printed product will have better glossiness of black and avoid the occurrence of machine internal scratches and color mixing phenomena.
5. Cultivate good operational habits and enhance work responsibility.
When doing any work, one must have a high sense of responsibility and a strong quality awareness. One must standardize the process operations and adhere to good traditional habits such as "three levels of flatness" and "three attentions". Taking the sample signing as an example, when comparing it with the sample, due to differences in distance, angle, light source, etc., visual perception will be distorted, resulting in inconsistent ink color. At this time, the signed sample must be taken off the sample and carefully compared; for long-run printing plates, they need to be baked to reduce ink color deviations caused by plate replacement; the rubber blanket should be cleaned frequently, and more absorbent paper should be placed after each cleaning to make the ink color stable; after the fly-over printing, the first five or six printed sheets with too deep ink color should be withdrawn; the printing speed should not be too fast, and it is important to maintain the stability and normal operation of the machine; when adding ink to the ink distributor, since the new ink is harder and has poorer fluidity, it should be stirred several times to avoid affecting the ink filling volume and causing ink color deviations.
Operators need to constantly learn, carefully observe and analyze, identify various factors that affect the color of the ink, and take corresponding measures to properly prevent and overcome them, striving to improve the stability and consistency of the ink color on the printed products, and effectively enhance the quality of the printed items.
