How to Control Offset of Offset Printing

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 the 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 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 not allowed, and the efficiency is not high.

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-drying deformation cannot be used. New paper must be processed or stored for a certain period of time to ensure the balance between temperature and humidity in the printing room. 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 printing is not easy to fast dry, causing the color printing 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, which will affect the stability of paper feeding. In the middle of the shutdown, the blankets should also be cleaned.

Method four, take measures to accelerate 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 air blowing tube's air-drying effect on the printed product. 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 appropriately increased, and the air volume can be adjusted to the maximum when the white paper is printed. 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 ink, control the size of the ink, check the overprinting situation at any time, identify problems, and stop the process in time.

Source: Print Information Network