At present, four-color offset printing presses have been very popular. The self-drying presses of well-known brands such as Heidelberg, Manland, and Manroland not only have good equipment performance, a high degree of automation, but also are equipped with an ink remote control system, which facilitates printing inks. Color control. reliable. However, in the actual printing process, it is not easy to achieve the ink color stability of each batch of printed products. In production, we often encounter quality problems caused by large differences in ink colors, causing great losses to the company. The following are some factors that affect ink stability.
1. Before printing, it is necessary to make a pre-adjustment based on experience
First of all, roughly adjust the ink volume of the ink cartridges of each color group according to the printing or printing plate text area. This kind of work is easier to achieve on a machine equipped with an ink remote control system. This should be greater than the estimated 80%, without printing in a wide range of inks, so as not to cause large color differences.
Secondly, according to the requirements of the production process list and the characteristics of the product, avoid formal paper printing in pre-adjustment, paper delivery, ink performance, pressure and other links. Among them, ensuring the reliability, continuity and stability of the paper is the most important. The experienced operator first adjusts the air blowing, suction, pressure foot, pressure spring, pressure roller, side edge, front edge, etc. according to the format and thickness of the paper to ensure the smooth feeding of the paper. Avoid dark color differences caused by different dark colors. It is recommended that experienced workers can adjust in advance.
Finally, in order to improve and ensure the normal printing process, the quality of the printing paper, the size of the printing area, the viscosity of the ink, the particle size and the ink should be appropriately adjusted to improve the printing quality of the printed product. Do not stop cleaning the rubber cloth and printing plate paper fur, and the ink skin and the ink are not the same because they don’t often stop cleaning. If various adhesives are added after printing and the ink oil is adjusted, there will be a certain color difference. In short, before the pre-setting work starts, it can greatly reduce the failure after the official printing, and the captain also has time and energy to focus on dark colors.
2. Correctly adjust the water and ink roller pressure
In the printing process, the text part of the printing plate must obtain a continuous and uniform amount of ink in order to obtain a printing effect with a consistent ink color. Therefore, in order to achieve good ink transfer, it is necessary to maintain proper contact and rolling relationships between the ink roller and the ink roller, and the ink roller and the printing plate. If this work is not reprocessed, the ink will be inconsistent. Therefore, each time the ink is installed, the ink method is used to adjust the pressure one by one, instead of the traditional plug test tension method, because the latter is due to the actual error caused by human factors. In the case of multi-color, it can not be used on high-speed machines. Up. As for the width of the ink roller, it is generally 4~5mm. First adjust the pressure between the ink transfer roller and the ink string roller, then adjust the pressure between the ink roller, the ink string roller, and the plate cylinder, and finally adjust the water transfer roller, the plate water roller, the string roller, and the intermediate roller. The pressure between the water and the printing plate cylinder is also dependent on the pressure between the plate water roller and the plate cylinder. The ink bar between these waterways is preferably 6mm.
After two or three months of use, this machine must be re-adjusted, because after a period of high-speed friction, the diameter of the drum will become smaller, especially in the drive. The pressure between the inks becomes smaller, and the accumulation of ink on the ink roller will not be passed down. When the ink roller reprints or stops reprinting, the amount of ink drops at this time, resulting in dozens or even hundreds of inks before the ink. Deeper, the ideal ink balance is difficult to achieve. This kind of failure is generally not easy to find, and only the finer printing in the printing process is more obvious. In short, the operation in this area must be careful, and the method must be scientific, otherwise the water, ink strips, and printed matter will be different in the color of the mouth and ink tip, which will cause artificial malfunction and increase the difficulty of operation.
3. Realize the balance of water and ink
As we all know, ink balance is an important part of offset printing. If the ink is very large, water emulsion of the ink will be produced, and of course the quality of the printed matter is not ideal.
First of all, make sure to properly adjust the pressure relationship between the water and the ink roller, and ensure that the fountain solution and alcohol content meet the general standards. On this basis, start the machine, turn off the water and ink rollers, and then stop to look at the printing plate, and the viscosity and dirtiness of the printing plate mouth are slightly worse. At this time, the water consumption is used as the initial water consumption for printing, which ensures the normal printing of general pictures and text products, and basically realizes the balance of ink and water.
Secondly, the water consumption can be flexibly adjusted according to factors such as large printing plate area, rough paper surface, addition of additives, printing speed and temperature, and ink humidity. In addition, when the machine is just turned on, the temperature of the body is very low. When the machine rotates at high speed for one to two hours, the temperature of the body, especially the temperature of the rubber roller, can double or even higher. At this time, the water The consumption gradually increases until the ink reaches a new equilibrium state.
It is not easy to achieve the balance between water and ink, and the operator must use the balance, otherwise the color stability of the ink is difficult to control, and the printed matter cannot be printed with high quality.
4. Sample calibration and color gradation arrangement
He said: “In the production process, the samples provided by the customer are very close, or only provide a color spray paint instead of proofing.” At this time, the specific situation should be analyzed in detail. It is not possible to use methods that are difficult to increase or decrease the amount of ink. Chasing effect. Although it is initially close to the printed matter, it does not guarantee the stability of the ink, thereby guaranteeing the final quality of the printed matter. In this regard, the printer should actively, seriously and responsibly exchange opinions with customers, point out the problems and revision suggestions in the sample draft, and make appropriate adjustments after obtaining consent.
The production of inks is usually to determine the color sequence of the multi-color machine by measuring the viscosity of the ink, because in the multi-color printing, the ink is combined in a wet and wet way. Only when the best ink viscosity is obtained can the ink be used. The color is stable and the printing is consistent. The printing order must be arranged in accordance with the characteristics and quality requirements of the printed matter, and must not remain unchanged. At the same time, the viscosity of the ink can also be adjusted. For example, a lithographic-based cover and a sky blue cover have a different printing order. The former turns green first, and the latter darkens first, then green. Otherwise, the color will darken, which is neither plain nor stable. Such as black printing, black should be arranged in the last color group as much as possible, so the printed product is better black, which can also avoid the dark color and color mixing inside the machine.
5. Develop good habits and enhance the sense of responsibility at work
To do any work, you must have a high sense of responsibility and a strong sense of quality, you must standardize the work process, and adhere to the good traditional habits of “Sanping” and “Sanqin”. Taking the sample sheet as an example, comparing the signature on the template, due to the difference in distance, angle, light source and other factors, it will cause visual deviation, resulting in unevenness before and after the ink. At this time, we must extract the signature sample from the template for careful comparison ;Long letterpress printing plates need to be baked to reduce the imperfections caused by incompleteness; the adhesive tape should be cleaned frequently, and more blotting paper should be placed after each cleaning to stabilize the ink; only need to remove from the five or six dark colors of the printing If the printing speed is not fast, the most important thing is to keep the machine stable and normal; add ink to the ink tank, because the new ink is hard and poor, it must be stirred several times to avoid affecting the amount of ink and causing ink deviation.
Operators should continue to research, observe and analyze, find out the factors that affect ink color changes from all aspects, and take corresponding measures to properly prevent and overcome them, improve the stability and consistency of printed ink colors, and improve the quality of printed products.