Analysis of Causes of Fluctuations in Gravure Overprinting

1. Overprint fluctuations caused by electrical faults
In general, the electrical part of a gravure register system consists of a detection section, a processing device, and an actuator. Any abnormal work at any point can cause overprint fluctuations. Therefore, in order to analyze the causes of overprint fluctuations, it is necessary to understand the electrical principles of the overprint system.
The following takes the gravure production line of French ATN company as an example to analyze the principles of overprinting electrical principles.

In each color printing unit, a pulse is generated every time the plate cylinder rotates, and it enters the code circuit board together with the 500 pulses generated by the encoder on the printing unit. After processing by the coded circuit board, four pulses are formed and sent to the longitudinal (or horizontal) registration circuit board. Here, the 4 pulse signals are compared with the 1 pulse signal from the cursor on the detection print. If the overprint occurs at this time, the register circuit board outputs a voltage of about 5 volts into the PLC. After PLC processing, then to the stepper motor driver, thereby promoting the action of the stepper motor, to achieve the purpose of register adjustment.

Checking for overprint fluctuations caused by electrical faults is generally done by following the method of checking. On the basis of understanding the electrical principles of the overprinting system, it is checked step by step whether the relevant electrical components are normal and whether the circuit is unblocked. However, after adjusting the registration of a particular machine with a certain type of gravure printing machine has considerable experience, you can also adopt a jumping mode of thinking, so that you can quickly find the fault point.

2. Overprint fluctuation caused by mechanical failure

Judging from practical experience, there is no fixed method for the mechanical inspection of overprint systems. Only after knowing and mastering the mechanical parts of the gravure printer, do you know which mechanical structures will affect the overprint and find the crux of the problem as soon as possible. Of course, because the “representation” of a mechanical failure is generally much more pronounced than the “presence” of an electrical failure, it is relatively easy to discover the overprint fluctuations caused thereby.

For example, after a long period of use of the impression cylinder, there will be more obvious signs of wear on the surface, which will affect the overlay accuracy. The thinner the substrate, the greater the impact on the overlay accuracy. In addition, if the impression cylinder is observed to vibrate continuously during the printing process, it is highly 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, often causing sudden jumps in the transverse overprint. In addition, the paper guide roller oscillates in the horizontal direction, and problems such as the stepping motor drive section may cause overprint fluctuations. Moreover, this type of overprint failure, its performance is basically in the production process from time to time there is a more substantial, sudden overprint.

3. Overprint fluctuations caused by other factors

In addition to electrical and mechanical reasons, overprint fluctuations caused by other aspects can not be ignored.

First, improper operation can cause overprint fluctuations. For example, if the tension size is not set properly, the tape will be loose at high speeds, affecting the longitudinal registration. For another example, if the oven temperature is set too high, it may cause the paper to be deformed after passing through the oven, affecting the overprint of the next color.

Second, raw materials and the production environment also have an impact on overprinting. Too loose paper will cause the actual tension to change frequently, increase the difficulty of operation, resulting in overprinting are mostly allowed in the longitudinal direction; the paper edge system will make the paper guide system non-stop action, affect the horizontal overprint. The temperature and humidity conditions in the production environment will have a certain influence on the size of the paper during the printing process.