Overprinting wave printing brings big troubles, how to solve it?
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Overprint fluctuations often cause a lot of trouble for printing, which affects printing efficiency. Here are three reasons why the problem of overprint fluctuations can be caused. Special attention is required during production.
1. Overprint fluctuations caused by electrical faults
In general, the electrical portion of the gravure register registration system consists of a sensing portion, a processing device, and an actuator. Any part of the work is not normal, it may cause overprint fluctuations. Therefore, in order to analyze the causes of overprint fluctuations, it is necessary to be familiar with the electrical principles of the overprint system.
Let's take a gravure production line as an example to analyze the electrical principle of overprinting.
In each color printing unit, each revolution of the plate cylinder produces a pulse that enters the code board along with the 500 pulses produced by the encoder on the printing unit. After processing by the encoding board, four pulses are formed and sent to the vertical (or lateral) register board. Here, the four pulse signals are compared with one pulse signal obtained by detecting the cursor on the printed matter. If the overprinting deviation occurs at this time, the register circuit board outputs a voltage of about 5 volts into the PLC. After being processed by the PLC, the stepper motor driver is driven to drive the stepping motor to achieve the purpose of register adjustment.
Checking for overprint fluctuations caused by electrical faults is generally a way to take a look. On the basis of understanding the electrical principle of the overprint system, check whether the relevant electrical components are normal and the circuit is smooth. However, after having considerable experience in adjusting the registration of a specific type of gravure printing machine, it is also possible to adopt a jumping thinking mode, so that the point of failure can be found more quickly.
2. Overprint fluctuation caused by mechanical failure
From the practical experience, there is no fixed method for the inspection of the mechanical aspects of the overprint system. Only after understanding and mastering the mechanical part of the gravure press, it is known that which mechanical structure will affect the overprinting, and the crux can be found as soon as possible. Of course, since the "appearance" of mechanical failure is generally much more pronounced than the "visualization" of electrical faults, it is relatively easy to find the resulting overprint fluctuations.
For example, after long-term use of the impression cylinder, the surface will have obvious wear marks, which will affect the overprint precision. The thinner the substrate, the greater the impact on overprint accuracy. In addition, if it is observed that the impression cylinder vibrates up and down during the printing process, it is likely that the impression cylinder bearing is damaged, which has an effect on the longitudinal registration of the printed product.
For another example, if the plate cylinder is not locked, there will be slight turbulence, which often causes a sudden jump in the lateral overprint. In addition, the paper guide roller is laterally swayed, and problems occur in the transmission part of the stepping motor, which also causes overprint fluctuations. Moreover, this type of overprinting failure, its performance is basically a large, sudden overprinting jump from time to time in the production process.
3. Overprint fluctuations caused by other factors
In addition to electrical and mechanical reasons, the overprint fluctuations caused by other aspects cannot be ignored.
First, improper handling can cause overprint fluctuations. For example, if the tension is not set properly, the paper will be loose and tight during high-speed operation, which will affect the vertical registration. For another example, if the oven temperature is set too high, it may cause the paper to deform too much after passing through the oven, which may affect the overprint of the next color.
Second, raw materials and production environments also have an impact on overprinting. If the paper is too loose, the actual tension will change frequently, and the operation difficulty will be increased. The overprinting is not allowed to be mostly in the longitudinal direction; the unevenness of the paper edge will cause the paper guiding system to stop moving and affect the lateral overprinting. The temperature and humidity conditions of the production environment will have a certain impact on the deformation of the paper during the printing process.