At present, four-color offset printing presses have become very popular. Heidelberg, Manroland, KBA and other well-known brands of offset printing machines not only have excellent equipment performance and high degree of automation, but also are equipped with an ink color remote control system, which makes the control of printed ink color convenient. reliable. However, in the actual printing process, it is not an easy task to make the ink color of each batch of printing stable. In production, quality problems caused by too much difference in ink color are often encountered, which causes great losses to the enterprise. The author has been operating the Heidelberg four-color offset press for more than 10 years. Now I will talk about my own understanding of some factors that affect the stability of ink color.

Before starting to print, we must make pre-adjustment work based on experience.

First, according to the area of ​​the proof or the printing plate, the amount of ink in each color group is roughly adjusted. This work is easier to accomplish on machines with an ink-coloured remote control system. There should be an estimate of more than 80% of this. Do not adjust the amount of ink in the printing area 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 Feida, delivery, ink performance, pressure, etc., to avoid the troubles in the formal printing. Among them, ensuring Feida's reliable, continuous and stable paper feeding is the most important. The experienced operators first adjust the blowing, inhalation, presser foot, compression spring, platen roller, side gauge, front gauge, etc. according to the width and thickness of the paper to smooth out the movement coordination between the components. The relationship ensures that Feida smoothly feeds the paper and avoids the difference in ink color caused by the flying. It is suggested here that experienced workers can make pre-adjustments to Feida.

In addition, it is necessary to adjust the viscosity, fluidity, and dryness of the ink in advance in order to improve the printing quality and ensure the normal printing. The color of the ink is different when the paper and the ink on the blanket and the printing plate are cleaned. If you add a variety of adhesives and varnishes in the middle of printing, the color deviation is certain.

In short, the pre-tuning work before starting the machine can greatly reduce the failure after the official printing, and the captain has time and energy to focus on the ink color.

Correct adjustment of water and ink roller pressure

In the printing process, the printing and printing parts must obtain continuous, uniform and appropriate amount of ink in order to obtain a print with consistent ink color. Therefore, between the ink roller and the ink roller, between the ink roller and the printing plate, proper contact and rolling relationship must be maintained to achieve good ink transfer. If the work is not done in detail and is incorrect, the ink will not be consistent. Therefore, each time the water and ink rollers are installed, the method of using the ink bar is used to adjust the pressure between them one by one, instead of the traditional method of testing the tensile force, because the latter is caused by various human factors. Larger, more disabled on multi-color, high-speed machines. As for the width of the ink stick, it is generally 4 to 5 mm. First adjust the pressure between the transfer roller and the squeezing roller, then adjust the pressure between the ink roller and the squeezing roller, the plate cylinder, and finally adjust the water transfer roller, the plate water roller, the water roller, the intermediate roller Between the pressure, and the pressure between the plate water roller and the plate cylinder, the ink bar between these waterways is preferably 6mm.

The equipment has to be re-adjusted 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 ink will not be able to pass down on the ink roller. When the fly reaches or stops and then resumes printing, because of the large amount of ink at this time, the first dozen or even hundreds of sheets are caused. The darkness of the ink is deep, and the ideal ink-and-wash balance is difficult to achieve. This fault is generally not easy to find, and it is only obvious when printing finer prints. In short, the operation in this area should be meticulous and the method should be scientific. Otherwise, it will cause the ink, the ink bar, the print mouth and the tip of the print to have different shades of ink, artificially causing the fault and increasing the difficulty of operation.

Achieve ink balance

As we all know, ink and water balance is an important part of offset printing. If the water is large and the ink is emulsified by oil-in-water, the quality of the printed product will of course not be ideal. Through long-term practice, the author has explored some skills.

First, 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, start up, close the water, ink roller, and then stop to view the printing plate, it is better to have a stick of about 3mm at the plate mouth. By using the amount of water at this time as the initial amount of printing, it is possible to ensure the normal printing of the general graphic products and basically achieve the ink-and-wash balance.

Secondly, according to other factors, the water consumption can be flexibly adjusted. For example, the printing plate has a large area, the surface of the paper is rough, the additive is added to the ink, and the printing speed and air temperature and humidity are changed.

In addition, the author also found that when the machine was just printed, the body temperature was low, and when the machine was running at high speed for an hour or two, the body temperature, especially the temperature of the rubber roller would more than double or even higher. The amount of water used will gradually increase until the ink reaches a new equilibrium.

It can be seen that it is not easy to achieve ink and water balance, and it requires the operator to weigh and use it. Otherwise, the stability of the ink color is difficult to control, and high-quality prints cannot be printed.

Correction and color sequence arrangement of proofs

This is often the case in production: the sample provided by the customer is not standard, or only a color spray is provided without proofing. At this time, it is necessary to analyze the specific situation. It is not possible to use the method of hardening the amount of ink or reducing the amount of ink to pursue the effect of the sample. Even if it is close to the proof, it can't guarantee the stability of the ink, so the final quality of the print cannot be guaranteed. In this regard, the printing factory should actively exchange opinions with customers in a serious and responsible manner, point out the problems and suggestions for revision of the draft, and obtain appropriate approval before appropriate adjustment and reprinting.

In the production, the ink color is usually used to determine the printing color sequence of the multi-color machine. Since the ink is overprinted in a wet-wet manner in multi-color printing, only the best overprinting rate can be obtained, and the ink color can be printed stably. 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-based cover and a sky-based cover have different print color sequences. The former is green and then red, the latter is magenta and then green, otherwise the overprinted color will be spotted. It is neither uniform nor unstable. For black-based prints, black should be arranged in the last color group as much as possible, so that the printed prints have better black gloss and avoid the occurrence of scratches and color mixing inside the machine.

Develop good operating habits and strengthen work responsibility

To do any work, we must have a high sense of responsibility and a strong sense of quality. We must standardize the process operation and adhere to the good traditional habits of "three flats" and "three times". Taking the sample as a case, in the signature sample on the control sample, due to the difference in distance, angle, light source, etc., the visual deviation will occur, resulting in inconsistency of the ink color. At this time, the signature sample must be taken off the template and carefully compared. The long version of the live printing plate needs to be baked to reduce the deviation of the ink color caused by the plate changing; the blanket should be cleaned frequently, and the ink should be put more stable after each cleaning; after the fly, The five or six inks that have just been printed are too deep to be drawn out. The printing speed cannot be greedy. It is important to keep the machine stable and normal. When adding ink to the ink fountain, it is necessary to stir a few times because the new ink is hard and the fluidity is poor. In order to avoid affecting the amount of ink, causing ink color deviation.

The operator should continue to study, carefully observe and analyze, find out the factors affecting the change of ink color from various aspects, and take corresponding measures to properly prevent and overcome, strive to improve the stability and consistency of the ink color of the printed products, and effectively improve the printed products. quality.

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