What caused the overprint fluctuations?

In general, the electrical department of a gravure register system consists of a testing department, 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 be familiar with the electrical principles of the overprint system.

The following takes the French ATN company's gravure production line as an example to analyze the electrical principles of overprinting.

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 four pulse signals are compared with one pulse signal obtained from the cursor on the detection print. If the overprint deviation 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 specific model of gravure printing machine has a similar experience, you can also take a jumping way of thinking, so that you can find the fault point faster.

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 grasping the mechanical department of the gravure printing machine, is it possible to know which mechanical structures will affect overprinting and find the crux of the matter as soon as possible? Of course, because the “representation” of a mechanical failure is generally much more pronounced than the “revealing” of an electrical failure, it is relatively easy to discover the overprint fluctuations caused thereby.

For example, after the long-term use of the impression cylinder, there will be more significant wear marks 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, which often causes the horizontal overprint to fluctuate. In addition, horizontal shifting of the paper guide roller, problems in the stepping motor transmission department, etc., can also cause overprint fluctuations. Moreover, this type of overprint failure, its performance is basically in the production process from time to time to throw up a more substantial, beating 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 manipulation can cause overprint fluctuations. For example, if the tension is not set properly, the paper belt will be loose and the longitudinal registration will be affected during high-speed operation of the equipment. 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 production environments also have implications for overprinting. Too loose paper will cause the actual tension to change frequently, increase the difficulty of manipulation, resulting in overprinting are mostly allowed in the longitudinal direction; unclean paper edges will cause the paper guide system to constantly move, affect the horizontal overprint. The temperature and humidity conditions of the production environment will have a certain influence on the size of the paper during the printing process.