1. Pre adjustment shall be done based on experience before printing
First, roughly adjust the amount of ink in the ink bucket of each color group according to the area of proofing draft or printing plate. On machines equipped with ink remote control system, this work is easier to complete. There should be an estimate of more than 80%. Don't adjust the ink amount in a large range while printing, so as not to cause great color difference.
Secondly, according to the requirements of the production process sheet and the characteristics of the product, adjust Feida, paper receiving, ink performance, pressure and other links in advance to avoid rush during formal printing. Among them, ensuring Feida's reliable, continuous and stable paper feeding is the most important. Experienced operators first adjust the blowing, suction, presser foot, compression spring, paper pressing wheel, side gauge, front gauge, etc. according to the width and thickness of the paper, straighten out the movement cooperation relationship between various parts, ensure Feida's smooth paper feeding, and avoid the difference of ink color caused by Feida's beating. It is suggested that experienced workers can adjust Feida in advance.
In addition, according to the paper quality and graphic area of the print, the viscosity, fluidity and dryness of the ink should be properly adjusted in advance to improve its printing suitability and ensure the normal printing. The ink color should not be different due to frequent shutdown to clean the paper wool and ink skin on the blanket and printing plate. If you add all kinds of adhesive remover and ink blending oil in the middle of printing, the color deviation is certain.
In short, by doing a good job of pre adjustment before startup, the faults after official printing can be greatly reduced, and the captain has time and energy to focus on the ink color.
2. Correctly adjust the pressure of water and ink roller
In the printing process, the image and text part of the printing plate must be continuously and evenly applied with an appropriate amount of ink in order to obtain a printing product with consistent ink color. Therefore, the proper contact and rolling relationship must be maintained between the ink roller and the ink roller, and between the ink roller and the printing plate, so as to realize the good transmission of ink. If this work is not done carefully and correctly, the ink color will not be consistent. Therefore, each time the water and ink rollers are installed, the ink rolling bar is used to adjust the pressure between them one by one, instead of the traditional method of feeler gauge tension test, because the latter has large actual errors caused by various human factors, which should be banned on multi-color and high-speed machines. As for the width of the ink rolling bar, it is generally 4 ~ 5mm. First adjust the pressure between the ink transfer roller and the inking roller, then adjust the pressure between the ink roller, the inking roller and the printing plate roller, and finally adjust the pressure between the water transfer roller, the plate water roller, the water transfer roller and the intermediate roller, as well as the pressure between the plate water roller and the printing plate roller. The ink bar between these waterways should be 6mm.
The equipment needs to 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. When the pressure between the ink rollers becomes smaller, the ink accumulated on the ink rollers will not be transmitted. When Feida stops printing or stops printing again, due to the large amount of ink at this time, the ink color of the first dozens or even hundreds of sheets is deep, and the ideal ink balance is difficult to achieve. This fault is generally not easy to find, and is more obvious only when printing fine prints. In short, the operation in this area should be meticulous and the method should be scientific. Otherwise, the ink color of the mouth and trailing tip of water, ink bar and printing will be different, which will artificially cause faults and increase the difficulty of operation.
3. Achieve ink balance
As we all know, ink balance is an important content in offset printing. If the water is large and the ink is large, so that the oil in water emulsification of the ink occurs, the printing quality will not be ideal. Through long-term practice, the author has explored some skills.
First, ensure that the pressure relationship between water and ink roller is properly adjusted, and the content of fountain solution and isopropanol meets the general standard. On this basis, start the machine, close the water and ink rollers, and then stop the machine to check the printing plate. It is better to have a slight dirt of about 3mm at the mouth of the printing plate. Taking the water volume at this time as the initial water volume of printing can ensure the normal printing of general graphic products and basically realize the balance of water and ink.
Secondly, the water consumption shall be flexibly adjusted according to other factors, such as the large graphic area of the printing plate, the rough surface of the paper, the need to add additives to the ink, and the change of printing speed, air temperature and humidity.
In addition, the author also found that when the machine just started printing, the body temperature is low, and when the machine runs at high speed for one or two hours, the body temperature, especially the cot temperature, will more than double or even higher. At this time, the water consumption will gradually increase until the ink reaches a new balance.
It can be seen that it is not easy to realize the balance of ink and wash, which requires operators to weigh and use dialectically. Otherwise, the ink stability is difficult to control and high-quality prints cannot be printed.
4. Proofing correction and color sequence arrangement
We often encounter such situations in production: the sample provided by the customer is very non-standard, or only one color spray draft is provided without proofing. At this time, we should analyze the specific situation. We can't use the method of hard increasing or reducing the amount of ink to pursue the effect of proofing. Even if it is close to the proofing draft at the beginning, the stability of the ink cannot be guaranteed, so the final quality of the printing cannot be guaranteed. In this regard, the printing factory shall actively exchange opinions with customers with a serious and responsible attitude, point out the problems existing in the sample and suggestions for modification, and make appropriate adjustment and re printing after obtaining consent.
In production, the printing color sequence of multi-color machine is usually determined by ink viscosity. In multi-color printing, the ink is overprinted together in a wet pressing and wet way. Only by obtaining the best overprint rate can we print prints with stable and consistent ink color. The arrangement of printing color sequence must be subject to the characteristics and quality requirements of printing products, not invariable. At the same time, you can also adjust the ink viscosity. For example, the printing color sequence of a purple based cover and a sky blue based cover is different. The former is first green and then magenta, and the latter is first magenta and then green. Otherwise, the overprinted color will be spot like, which is neither plain nor stable. For example, for black based prints, black should be arranged in the last color group as far as possible. In this way, the printed prints have better black gloss and avoid scratches and color mixing inside the machine.
5. Cultivate good operation habits and strengthen the sense of responsibility
To do any work, we must have a high sense of responsibility and strong quality awareness, standardize process operation, and adhere to good traditional habits such as "three leveling" and "three diligence". Take the example of frequently checking the sample sheet. When comparing the signature words on the template, due to the different distance, angle and light source, the vision will deviate, resulting in inconsistent ink color. At this time, the signature words must be removed from the template and compared carefully; Long version live printing plate needs baking to reduce the ink deviation caused by plate change; The blanket should be cleaned frequently, and more blotting paper should be put after each cleaning to stabilize the ink color; After Feida's printing, the five or six newly printed inks are too deep 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 bucket, because the new ink is hard and has poor fluidity, it should be stirred several times to avoid affecting the amount of ink and causing ink color deviation.
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