When printing single-dual-color offset presses on multi-color prints, four-color overprint deviations are often a headache for workers. The first two colors are generally no problem, but the latter two colors are difficult to control. Normally, it can only reduce the speed of the machine, reduce the amount of ink, adjust the fluidity of the ink and spray powder, but the effect is not great. The above measures will also affect the work efficiency and product quality, and at the same time bring a double increase in labor intensity.
In fact, we can divide printing into "dry and wet". The so-called "wet printing" means that the two overprints on the substrate are wet and wet, that is, the overprint starts immediately after the previous color is printed; while "dry printing" is to print the first color after drying and then print the next color. Single-color machine printing four-color products.
1. Dry printing
The advantage of this printing method is that it can ensure the stable positioning of the paper in the subsequent printing, and the overprinting position is basically fixed. In addition, dry ink overprinting can obtain full, bright and accurate colors. However, due to a certain amount of downtime, it is easy to cause paper deformation and inaccurate overprinting, and the efficiency is not high.
2. Wet printing
This printing method saves time, and the paper is accurately overprinted due to small deformation. But it has many problems, such as easy to cause the back side to be dirty, the color of the printed product is dark, the amount of ink is large or the printing area is large, the post-printing order color paper is difficult to position, which affects the accuracy of overprinting. If there is a four-color offset printing machine, these problems are not there, and the use of single-color and two-color offset printing machines can only be solved by experience. How to "weaken time" in wet printing is the goal of our exploration.
Method one: Check the printing paper's status to be printed. Paper with high humidity or air-drying deformation can not be used. Newly-entered paper should be dried or stored for a certain period of time to ensure its balance with the temperature and humidity of the printing workshop. Cut the paper to ensure that its edges are neat and smooth, to ensure the stability of the paper;
Method 2: Do not put less or less additives such as thinner and ink oil in the ink, because it affects the color and it is easy to cause the back to be smudged. The printed ink is not easy to dry quickly, causing the subsequent color printing to go away Difficult paper positioning directly affects the accuracy of overprinting;
Method 3. Before printing, especially before printing on coated paper with quick-drying ink, make sure that the blanket is dry and clean to prevent the blanket from sticking to the paper due to the semi-dry state of the front imprint and affecting the stability of the paper. When the machine is shut down in the middle, the blanket should also be cleaned;
Method four: Take measures to accelerate the drying of the previous semi-finished printing products. Here, the arc-shaped paper guard outside the paper feed roller can be converted into an electric oil film for heat treatment. In addition, the powder spraying device should be used flexibly. The first two colors do not need powder spray to maintain the air-drying effect of the blower tube on the printed product. The air volume is adjusted according to the thickness of the paper. The air volume of the general advanced four-color printing paper can be increased appropriately. The air volume can be adjusted to the maximum when printing on whiteboard paper. In order to make the printed products get sufficient air-drying effect. After the hot air drying device is installed, the ink is basically dry before the printed matter arrives at the receiving table, which does not cause the back to be dirty, and ensures the correct paper positioning during the subsequent color printing. In this way, the wet printing seems to become Dry printing without time intervals not only guarantees the accuracy of overprinting, but also solves the problems of dirty printing and poor drying.
The above measures are based on the requirements of conventional printing. The printing operator must operate carefully, master the balance of water and ink, control the amount of ink, check the situation of overprint at any time, find problems, and stop processing in time.
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