When printing multicolor prints using a single-color offset press, four-color overprint deviations are often a headache for workers. The first two color overlays generally have no problem, but the latter two colors are difficult to control. In general, measures such as reducing the speed of the machine, reducing the amount of ink, adjusting the ink flowability, and dusting are not effective, and the above measures will also affect work efficiency and product quality, and at the same time, the labor intensity will increase exponentially. In fact, we can divide printing into "dry and wet" two kinds. The so-called "wet printing" is the printing on the substrate twice before and after printing wet and wet, that is, the previous color has just been printed after the start of overprinting; and "dry printing" is printed after drying a color, such as the use of Monochrome printing four-color products.
Dry printing
The advantage of this printing method is that it can ensure that the positioning of the paper in the subsequent printing is stable, and the overprint position is basically fixed. In addition dry ink overprinting can obtain full, vivid and accurate colors. However, due to a certain amount of downtime, it is easy to cause paper deformation and overprinting is inaccurate, and the efficiency is not high. In the event of an emergency, it cannot be completed.
2, wet printing
This printing method saves time and the overlay of the paper is accurate due to small deformation. However, it has many problems, such as easy to cause the back of the dirty, the color of the printed product is dark, the ink is large or the printing area is large, the positioning of the printed paper after printing is difficult, and the accuracy of overprinting is affected. If there are four-color offset presses, there is no such problem. The use of single- and double-color offset presses can only be solved by experience. How to reduce the time of wet printing is our goal.
Method 1. Check the state of the printed paper to be printed. The paper with high humidity or air-dried deformation cannot be used. The newly-entered paper is subjected to paper processing or stocking for a certain period of time to ensure its balance with the temperature and humidity of the printing shop. Cut the paper to ensure that its edges are neat and smooth to ensure the paper's stability;
Method two, ink is not put or put thinner, dilute oil and other additives containing more fatty oils, because it affects both the color and easy to cause the back of the dirty, ink prints are not easy to fast dry, causing the color printing after the walk Paper positioning difficulties directly affect the accuracy of overprinting;
Method 3: Before printing, especially before printing with fast-drying ink on coated paper, ensure that the blanket is dry and clean to prevent the blanket from adhering to the paper due to the semi-dry state of the previous imprint and affect the stability of paper feeding. In the middle of the shutdown, the blankets should also be cleaned.
Method 4: Take measures to speed up the drying of the semi-finished products in front. Here, the arc-shaped paper holder outside the paper feed roller can be converted into a fuel oil tablet for heat treatment. In addition, it is necessary to use the powder spraying device flexibly. The first two colors do not need dusting agent to keep the blowing pipe dry on the prints. The air volume is adjusted according to the thickness of the paper. Generally, the air volume of the advanced four-color printing paper can be increased to some extent. When the white paper is printed, the air volume can be adjusted to the maximum. In order to obtain sufficient air drying effect of the prints. After the hot air drying device is installed, the ink is almost dry before the printed product arrives at the delivery table, which does not cause back rubbing, and ensures correct paper positioning during subsequent color printing. In this way, the wet printing seems to have become Dry printing with no time interval not only guarantees the accuracy of overprinting, but also solves problems such as dirty prints and poor drying of printed products.
The above measures are based on conventional printing requirements. The printing operator must operate carefully, master the balance of ink and water, control the size of the ink, check the overprint situation at any time, find problems, and stop the process in time.
Reprinted from: Fuzhou Printing Network