In the print production of color newspapers, overprinting is almost the most important criterion for evaluating the quality of newspapers. In actual production, there are many factors that can affect the accuracy of color newspaper registration. It can be said that almost all the links that touch printed newspapers in color newspaper production can affect the overprinting of newspapers, such as photoprinting, printing, paper, and fountain solution. , printing process, printing equipment and so on. In this article, we will discuss some representative issues that affect the quality of overprinting.

Prepress:

(1) Photographic process leads to:

After the color graphic is processed by prepress and imposition, it is finally exposed on the film by a laser imagesetter. This exposure is separated by color on the four-color film by the imagesetter. However, due to the influence of mechanical transmission and other factors, the complete correspondence between the four films cannot be achieved (in the sense of registering). This kind of error is always present and cannot disappear because of the improvement of the operation level.

(2) Film imposition error

In many printer manufacturers, because there is no directly facing phototypesetter, only four open or smaller films can be used to make collages and then print. However, since this process is a manual operation process, high requirements are placed on the operator's skill and level of detail. The same imposition process, for different degrees of operator, the result will definitely not be the same. However, even the best make-up and copy-printing operators will never achieve this kind of overprinting error. This kind of registration error is always objective.

(3) Plate punching and bending errors

The stencil must be punched and bent before the machine goes to the machine. However, since this operation still depends on the operation of the user to a great extent, no matter how elaborate the special equipment used, the error cannot be avoided. .

The above three points are all links in the prepress process that are likely to have an impact on the printing overprint. Although we found that the overprinting error in each link is not very large, and the error of any single link is not enough to generate overprints under normal circumstances. This is a serious impact, but we also mentioned that since these errors can only be reduced and cannot be avoided, the impact of overlaying errors on printing overprints cannot be ignored. It can be seen that the improvement of the quality and sense of responsibility of the operators in the pre-press link is very important for overprinting of color newspapers.

Printing process:

The factors affecting the stability of the tape tension (such as the tension error caused by the tension control system to make the tape tension unstable) and the factors affecting the precise transfer of the graphic image (such as the bearing wear of the printing press roller. The pressure is not normal, the axis of the roller is not parallel, the positioning pin of the printing plate is offset, and so on, so that newspaper printing plate images can not be accurately transferred to generate overprinting errors).

(1) Factors affecting the stability of the tape tension

Different types of high-speed roller presses have different methods and methods for controlling the tension of the tapes. The paper feeding routes between the printing units of the printing presses are also different. Judging from the current mainstream equipment used in domestic color printing, the following printing components will have an impact on color registration:

During the printing process, the tension of the tape is affected by the above components. Any problems with any component will affect the stability of the tape tension. This in turn affects the accuracy of newspaper registration. The following is a detailed analysis of the impact of various components on color newspaper registration.

1 paper holder.

The brake pads of the tensioning and braking system of the printing machine paper frame paper roll wear. The change in the gap between the brake pad and the brake disc and the leakage of the brake seal airbag will have a great influence on the stability of the tension of the tape.

2 floating roller.

The floating roller is an important component to ensure the stability of the printing tape tension in the printing process of newspapers. Tension control generally refers to a tension control system composed of an air control element, a cylinder, a floating roller, and the like, which maintains a stable tension during the printing process. The mechanical factors affecting the color registration in this section include the wire connecting the slider at both ends of the floating roller, the sliding guide and the sliding bearing on the slider. In actual production, when there is a change in the paper, such as changing the paper, loading a new paper roll, etc., if the wire in the part is fastened. Sliding bearings and rails work well, and the floating roller reacts sensitively to changes in the tape, so the tension of the tape during printing is good; conversely, if the steel wire is slack, the sliding bearing is dry and oil is missing, or the paper ash is accumulated on the guide rail, making The floating roller is unresponsive to the change of the tape, and the tension stability of the tape is poor.