Analysis of Causes of Overprint Fluctuation in Gravure Process
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In the process of gravure printing, the phenomenon of overprint fluctuations often occurs, and its influencing factors are many, and it is not easy to detect, and it is difficult to handle. This article only analyzes from the following aspects.
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 work that is not working properly 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 the gravure production line of ATN Company of France 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 overprinting 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 fluctuations 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 parts of the gravure press, it is well known which mechanical structures will affect the overprinting, so that the crux can be found as soon as possible. Of course, since the "appearance" of mechanical failure is generally much more pronounced than the "appearance" of electrical faults, it is relatively easy to find the resulting overprint fluctuations.
For example, after long-term use of the impression cylinder, there will be obvious signs of wear on the surface, which will affect the accuracy of overprinting. 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, the performance of this type of overprinting failure is basically a large, sudden overprinting jump from time to time during 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.
In short, there are many reasons for the influence of gravure overprinting, and the degree of influence is large or small. However, as long as we carefully observe and carefully summarize, we will be able to find out the crux of the overprinting, so as to achieve the purpose of quickly eliminating faults and ensuring product quality.