Reasons and solutions for overprinting in gravure printing machine

Editor's note: With the increasingly fierce competition in the printing industry, people are increasingly demanding the sense and quality of packaging. The gravure printing machine has become the mainstream of today's printing industry because of its unique printing technology, high output, low loss and other advantages. Moreover, there are more and more types of gravure printers, and the overall machine configuration and control system are different, but the working principle is not very different, and the resulting failures are somewhat similar. In the production process, overprinting of printed products is not allowed, and the impact on product quality is one of the problems with gravure printing. This article does some analysis and discussion on the reasons and treatment in this regard for the reference of industry insiders.

First, the paper shrinks severely during printing, resulting in inaccurate registration

Paper is one of the essential raw and auxiliary materials for printing on paper. Due to the influence of outside temperature and humidity, as well as the improper control of temperature and humidity in the printing shop, it has a certain influence on the wet and dry properties of the paper. During printing, the temperature of the drying box of each color group is set too high, the paper is severely shrinking, and the color printing sets have different degrees of deviations and jitters, resulting in overprinting of “darkness”. The intensity of the received light signals received by the computer automatic tracking printing system is different. The overprint marking can be locked in a specific position, causing overprint deviations and affecting the quality of printed products. The general treatment method is to keep the printing shop constant temperature and humidity, and reduce the temperature of the drying box properly.

Second, the embossing roller controls the pressure imbalance, resulting in beating, affecting the registration

The appearance of this phenomenon first excludes human factors (such as when the imprinting roller is not fully aligned and misaligned). The pressure imbalance between the two ends of the platen roller is a major factor in the gas leakage of the air line system. This causes the cylinder connecting the two ends of the platen roller to fail to maintain the platen roller during printing due to insufficient air pressure or unbalanced pressure adjustment at both ends. Constant, resulting in run up and down, a long time caused by the deformation of the outer surface of the impression roller, paper tension is tight, resulting in overprinting is not allowed. The treatment method is to check the air circuit system to ensure that the air path does not leak, and replace the air leakage pneumatic components and replace the new embossing roller so that the embossing roller and the printing plate are in good agreement during printing.

Third, track the electric eye's own problem caused by overprinting is not allowed

The tracking electric eye is an inductive photoelectric sensor. Its working principle is to sense the color by inductive printing, convert the reflected and added optical signal into an electric signal, and process it through an analog/digital conversion circuit to send the digital signal to a computer for positioning and tracking. . If the distance between the electric eye and the printed mark is too far away, the spotlighting spot of the electric eye is not directly marking the printed mark, the electric powder covered with the mirror outside the electric eye, and the glowing light in the electric eye will cause the Jiang signal to become weak, or no light signal returns. As a result, the computer tracking system was slow to follow up and malfunctioned. It was unable to correct the overprint deviation in a timely manner, resulting in overprinting of printed products. The general treatment method is to clean the surface of the electric glasses, adjust the distance between the paper and the electric eye, and mark the mark for printing. If it is found that the electric light bulb is burned out, replace it in time, and carefully observe the computer overprint waveform until the printing mark is stable. .

Fourth, the paper feeding force is not set properly or the tension device fails

The gravure printing machine has many color groups and long paper feeding distances. In order to ensure the stability of the paper feeding, a set of tension buffer device is generally set at the paper inlet and the paper outlet. According to different characteristics of paper (such as paper thickness, thin; dry, humidity; ambient temperature, humidity, etc.) and set the tension size, if the tension parameters are not set properly, or the tension device fails, will cause the coated paper to appear in the left and right shaking Printing hues and cross markings cannot be kept within a valid range of rotation, which will cause the printing marks to flutter around and the printing products will be deviated. The general treatment method is to set the paper feeding force parameter value according to the characteristics of the coated paper so that the coated paper can be transported stably. If the tension device is faulty, the electrical technician is required to repair it.

Fifth, part of the automatic register tracking system is out of control or does not work

The automatic register tracking system is a print-registered "neutral midrib" that analyzes and processes the light signal from the tracking eye and conveys the processed control commands to the registration control version of each printing color group to make the control instructions. It is converted into an electrical signal and sent to the corresponding register motor for automatic adjustment overprint deviation. Any failure in a certain part of the work will cause the register motor to run out of control or stop working. It is impossible to correct the deviation of the printed product in time, resulting in inaccurate overprinting. The general approach is to check each link step by step, until the problem is found, resulting in failure of the automatic register tracking system, in most cases caused by the failure of the registration control board itself, but does not rule out the overprinting motor itself has problems. To further determine whether the problem lies with the control board, a new control board can be used, or the control board can be swapped with other color groups to perform tests to find out the problem. If the control board is normal, the problem lies in the overprinting motor repair. The motor can be.

6. The transmission gear and plate shaft are not locked, causing the plate cylinder to shift

Each color group of the gravure printing machine has a set of independent locking devices to connect the plate shaft with the transmission gear. Once the locking device is not locked, it will cause the plate cylinder to move back and forth when the plate cylinder is not locked due to the plate axis being locked at high speed. Overprinting is not allowed. The processing method is to check whether the locking device is damaged, whether the transmission gear and the plate shaft are slipped and locked.