At present, four-color offset printing presses have become very popular. Heidelberg, Manroland, KBA, and other well-known offset presses not only have excellent device performance and high degree of automation, but also have an ink-colored remote control system to facilitate the control of printing ink color. reliable. However, in the actual printing process, it is not an easy task to ensure that the ink color of each batch of printed products is stable. In production, the quality problems caused by the large difference in ink color are often encountered, causing great losses to the enterprise. The author has been operating the Heidelberg four-color offset press for more than 10 years and is now talking about his understanding of some factors that affect the stability of ink color.
1. Before printing, it is necessary to make pre-adjustment work based on experience
First, according to the area of â€‹â€‹the proof sheet or plate graphic, roughly adjust the ink amount of the ink fountain in each color group. On machines equipped with an ink-based remote control system, this work is easier to accomplish. There should be more than 80% of this estimate. Do not adjust the amount of ink while printing, so as not to cause a large color difference.
Secondly, in accordance with the requirements of the production process and the characteristics of the product, various aspects such as feeder, delivery, ink performance, and pressure are adjusted in advance to avoid rushing during formal printing. Among them, it is the most important to ensure Federer's reliable, continuous and stable transport of paper. The experienced operators first adjust the blowing, suction, presser foot, compression spring, pressure roller, side gauge, and front gauge according to the width and thickness of the paper, and rationalize the movement between the components. The relationship ensures that feeders can feed paper smoothly, avoiding the dark shades of ink caused by feeders. It is recommended here that experienced workers can make advance adjustments to feeders.
In addition, it is necessary to adjust the viscosity, fluidity, and drying properties of the ink in advance in accordance with the quality of the paper used in the print and the area of â€‹â€‹the image, so as to improve the printability and ensure the normal printing process. Shut down the blankets and ink and ink on the printing plates to create different shades of ink. If you add a variety of retreating agents and inks to the middle of printing, the color deviation is positive.
In short, the pre-tuning work before the start of work well, you can greatly reduce the failure after the official opening of India, the captain also has the time and energy focus on good ink.
2. Adjust water and ink roller pressure correctly
In the printing process, the graphic part of the printing plate must obtain continuous, uniform and appropriate amount of ink in order to obtain a uniform ink product. Therefore, an appropriate contact and rolling relationship must be maintained between the ink roller and the ink roller, and between the ink roller and the printing plate, in order to achieve good ink transfer. If this work is done indefinitely and incorrectly, the ink will not be consistent. Therefore, each time water and ink rollers are installed, they insist on using the method of rolling the ink bars to adjust the pressure between them one by one, instead of using the traditional method of measuring the force of the feeler, because of the actual error caused by various human factors. Larger, more to be disabled on multicolor, high-speed machines. As for the width of the rolling stick, it is usually 4~5mm. First adjust the pressure between the ink transfer roller and the ink roller, and then adjust the pressure between the ink roller and the ink roller and the plate cylinder. Finally, adjust the water transfer roller, water roller, water roller, and intermediate roller to each other. Between the pressure and the pressure between the plate roller and the plate cylinder, the ink bar between these waterways is preferably 6mm.
After the equipment has been used for two or three months, it needs to be readjusted because the ink roller will become smaller in diameter after a period of high-speed friction, especially in the transmission. The pressure between the rollers becomes smaller, and the ink accumulates on the roller. It can't be transmitted. When the feeder reaches a stop or stops and reprints, due to the large amount of ink at the moment, the first tens or even several hundred sheets are created. The darker ink, the ideal ink balance is difficult to achieve. This failure is generally not easy to find, and it is only evident when printing finer prints. In short, the operation in this area must be meticulous and the method should be scientific. Otherwise, it will cause water, ink bars, printed products to gargle, and the tip of the ink to have different shades of ink. It artificially causes malfunction and increases the difficulty of operation.
3. Achieve ink and water balance
As we all know, ink-water balance is an important part of offset printing. If the water is large and large, and the ink is oil-in-water emulsified, the quality of the print will not be ideal. Through long-term practice, the author has worked out some techniques.
First of all, ensure that the pressure relationship between the water and the ink roller is properly adjusted, and the contents of the fountain solution and isopropyl alcohol meet the general standards. On this basis, turn on the machine, close the water and ink roller, and then stop to check the printing plate. It is advisable to use a slightly dirty 3mm thick plate at the mouth of the printing plate. By using the amount of water at this time as the initial amount of printing water, normal printing of general graphic products can be guaranteed, and ink-water balance can basically be achieved.
Second, according to other factors, flexible adjustment of water consumption, such as the large plate area, the paper surface is rough, the ink needs to add additives, printing speed and air temperature, humidity and other changes.
In addition, the author also found that when the machine was just printing, the body temperature was low, and when the machine was running at high speed for one or two hours, the body temperature, especially the temperature of the roller, would more than double or even be higher. The water consumption will gradually increase until the ink reaches a new equilibrium.
It can be seen that to achieve ink-water balance is not easy, and operators need to weigh and use different methods. Otherwise, the stability of the ink is difficult to control and no high-quality prints can be printed.
4. Correction of the sample draft and color order arrangement
Often encountered in the production of the situation: the customer to provide proof is not standard, or not proof only to provide a color inkjet. At this time, it is necessary to analyze the specific situation in detail, and it is not possible to use the method of increasing the amount of ink or reducing the amount of ink to chase the effect of the sample draft. Even if you start to get close to the proofs, the stability of the ink cannot be guaranteed and the final quality of the prints cannot be guaranteed. In this regard, printing houses should actively and positively exchange opinions with customers and point out the problems and suggestions for amendments to the sample drafts. After obtaining approval, they can make appropriate adjustments and printing.
In production, ink viscosity is usually used to determine the color sequence of a multicolor machine. In multi-color printing, the ink is superimposed together in a wet and wet manner. Only when the optimal rate of overprinting is obtained, the ink can be printed stably. Consistent prints. The arrangement of the printing color sequence must be subject to the characteristics and quality requirements of the printed product, but it cannot be changed. At the same time, ink viscosity can also be adjusted. Such as a purple-based cover and a sky-blue cover, the printing color sequence is different, the former first green magenta, the latter first magenta after the green, otherwise the overprinted color will be spotted It is neither fair nor stable. For black-based prints, black should be arranged as far as possible in the last color group, so that the printed product, the black gloss is better, and it also avoids the occurrence of scratches and color mixing inside the machine.
5. Cultivate good operating habits and strengthen work responsibility
To do any work must have a high sense of responsibility and a strong sense of quality, we must standardize the process operation, adhere to the "Sanping", "Sanqin" and other good traditional habits. Taking Duan Zhang as an example, in the case of a signature sample on a control template, due to differences in distance, angle, and light source, the vision will be biased, resulting in inconsistent ink colors. In this case, the signature must be removed from the template and carefully compared. Only for long-lived printing plates, baking plates are needed to reduce ink miscoloration caused by changing plates; blankets should be washed frequently, and more ink should be placed on the ink after each cleaning; ink is stable; The five or six inks that have just been printed are too deep to be drawn out. The printing speed cannot be rushed. The important thing is to keep the machine stable and normal. When ink is added to the ink fountain, the new ink is hard and the flowability is poor, so it is necessary to stir a few more times. , so as not to affect the amount of ink, causing ink deviations and so on.
Operators should constantly study, observe and analyze carefully, find out the factors that affect the change of ink in all aspects, and take corresponding measures to properly prevent and overcome them, and strive to improve the stability and consistency of the inks of printed products and improve the printed products. quality.
Reprinted from: Screen Printing Industry
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