At present, four-color offset printing machines have become very popular. Heidelberg, Manroland, KBA and other well-known brand offset printing machines not only have excellent equipment performance and high degree of automation, but also are equipped with a remote control system for ink color, which makes printing ink color control convenient reliable. However, in the actual printing process, it is not an easy task to stabilize the ink color of each batch of prints. In production, quality problems caused by too large ink color differences are often encountered, causing great losses to the enterprise. The author has operated Heidelberg's four-color offset press for more than 10 years, and now I will talk about my own understanding of some factors that affect the stability of ink color.
Before printing, it is necessary to do pre-adjustment work based on experience
First of all, according to the area of ​​proofing or printing plate and text, roughly adjust the lower ink volume of each color group ink fountain. On machines equipped with a dark-colored remote control system, this task is easier to complete. In this regard, there should be more than 80% of the estimation, do not adjust the ink volume in a large range while printing, so as not to cause a large color difference.
Secondly, according to the requirements of the production process sheet and the characteristics of the product, pre-adjust the various links such as feeder, paper collection, ink performance, pressure, etc. to avoid confusion during the official printing. Among them, it is most important to ensure that Feida feeds paper reliably, continuously, and steadily. Experienced operators first adjust the air blowing, suction, presser foot, pressure spring, pressure roller, side gauge, front gauge, etc. in advance according to the size and thickness of the paper, and straighten out the movement coordination between the parts Relationship to ensure that Feida feeds paper smoothly and avoids ink shades caused by Feida hitting. It is suggested here that experienced worker masters can make advance adjustments to Feida.
In addition, according to the quality of the paper used for the printed matter and the size of the graphic area, the viscosity, fluidity, and dryness of the ink should be adjusted in advance to improve its printability and ensure that the printing is carried out normally. Shut down to clean the paper wool and ink skin on the blanket and the printing plate, resulting in different shades of ink. If you add various debonding agents and ink-adjusting oil in the middle of printing, it is certain that color deviation occurs.
In short, by doing a good job of pre-adjustment before starting up, you can greatly reduce the failure after the official start of printing, and the captain has time and energy to focus on the ink color.
Correctly adjust the water and ink roller pressure
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 printed product with consistent ink color. Therefore, between the ink roller and the ink roller, and between the ink roller and the printing plate, it is necessary to maintain a proper contact and rolling relationship in order to achieve a good transfer of ink. If this work is not done carefully and incorrectly, the ink color will not be consistent. Therefore, each time the water and ink rollers are installed, the method of rolling the ink stick is used to adjust the pressure between them one by one, instead of the traditional method of using a feeler gauge to test the pulling force, because the actual error of the latter due to various human factors Larger, more disabled on multi-color, high-speed machines. As for the width of the ink rolling bar, generally 4 to 5 mm is suitable. First adjust the pressure between the ink transfer roller and the cross-ink roller, then adjust the pressure between the inking roller, cross-ink roller, and plate cylinder, and finally adjust the water transfer roller, the plate water roller, the water cross roller, and the intermediate roller to each other. The pressure between them also depends on the pressure between the plate water roller and the plate cylinder. The ink bar between these several water channels should be 6mm.
The equipment will be readjusted after two or three months of use, 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 ink rollers becomes smaller, and the accumulation of ink on the ink rollers will not be transmitted. When the feeder stops or stops printing and then resumes printing, due to the large amount of ink at this time, the first dozens or even hundreds of sheets The ink color is dark, and the ideal water-ink balance is difficult to achieve. This fault is generally not easy to find, and is only obvious when printing finer prints. In short, the operation in this respect should be meticulous and the method should be scientific, otherwise it will cause the ink color of the gripper and trailing part of the water, ink bar, printed product to be different in shade, artificially causing a malfunction and increasing the difficulty of operation.
Achieve water and ink balance
As we all know, water-ink balance is an important part of offset printing. If the water is large and the ink is large, and the ink is emulsified with oil-in-water, the print quality will of course not be ideal. Through long-term practice, the author explored some techniques.
First of all, make sure that the pressure relationship between the water and the ink roller is adjusted properly, and that the contents of fountain solution and isopropyl alcohol meet 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 better to have a slight stickiness of about 3mm at the mouth of the printing plate. Using the water volume at this time as the initial water volume for printing can ensure the normal printing of general graphic products, and basically achieve water-ink balance.
Secondly, flexibly adjust the water consumption according to other factors. For example, the printing plate area is large, the paper surface is rough, additives need to be added to the ink, and the printing speed and air temperature and humidity change.
In addition, the author also found that the temperature of the fuselage was lower when the machine was just printed, and when the machine was running at high speed for an hour or two, the temperature of the fuselage, especially the temperature of the rubber roller, would more than double or even be higher The water consumption will gradually increase until the ink and wash reach a new equilibrium state.
It can be seen that achieving ink-and-ink balance is not an easy task. It requires the operator to weigh and use the dialectic in multiple ways. Otherwise, ink color stability is difficult to control, and high-quality prints cannot be printed.
Proofing and color sequence arrangement
It is often encountered in production: the sample provided by the customer is very non-standard, or only a color printing is provided without proofing. At this time, it is necessary to analyze the specific situation in detail, and the method of hardening the ink volume or reducing the ink volume cannot be used to track the effect of the proof. Even if it is initially close to the proofing, it cannot guarantee the stability of the ink color, and thus cannot guarantee the final quality of the printed product. In this regard, the printing house should actively exchange opinions with customers in a serious and responsible manner, point out the problems and revision suggestions of the sample draft, and obtain appropriate consent before appropriate adjustment and reprinting.
In production, the printing color sequence of the multi-color machine is usually determined by the viscosity of the ink. Because in the multi-color printing, the ink is overprinted together in a wet press wet mode, only when the best overprint rate is obtained can the ink color be stable, Consistent prints. The arrangement of the printing color sequence must obey the characteristics and quality requirements of the printed products, and cannot be fixed. At the same time, the viscosity of the ink can also be adjusted. For example, a purple-dominated cover and a sky-blue dominated cover have different printing color sequences. The former has cyan first and then magenta, and the latter has magenta first and then cyan, otherwise the overprinted colors will appear speckled. , Neither uniform nor unstable. For black-based prints, black should be arranged in the last color group as much as possible. The blackness of the printed prints is better, and the occurrence of scratches and color mixing in the machine is avoided.
Cultivate good operating habits and strengthen work responsibility
Any work must have a high sense of responsibility and a strong sense of quality, must standardize the process operation, adhere to the "Sanping", "Sanqin" and other good traditional habits. Taking Qinqian proofs as an example, when comparing the signatures on the template, the difference in distance, angle, light source, etc. will cause deviations in vision, resulting in inconsistent ink colors. At this time, the signatures must be removed from the template and carefully compared. It ’s okay; long-lived printing plates need to be baked to reduce the ink color deviation caused by the plate change; the blanket should be cleaned frequently, and more ink-absorbing paper should be placed after each cleaning to stabilize the ink color; The five or six inks that have just been printed are too dark to be drawn out. The printing speed should not be greedy. The important thing is to keep the machine stable and normal. When adding ink to the ink fountain, because the new ink is hard and has poor fluidity, it needs to be stirred a few more times. , So as not to affect the ink volume, causing ink color deviation, etc.
Operators should continuously study, carefully observe and analyze, find out the factors that affect the ink color change from all aspects, and take corresponding measures to properly prevent and overcome, strive to improve the stability and consistency of the ink color of the printed product, and effectively improve the printed product quality.
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