Factors Affecting Plastic Gravure Overprinting

Abstract: This article briefly and briefly analyzes the basic principle, process and operating conditions of overprinting, and the influence of printing plate rollers, raw and auxiliary materials, and environment on the print registration.

In the plastic gravure printing process, overprinting is one of the most common printing problems. The national standard GB7707-87's requirement for printing registration is that the main part of the field is within 0.5mm, and the main part of the layer is within 0.3mm. The market competition makes the customer's requirements for printing more and more stringent. In fact, there are many live jobs, especially the packaging of some well-known enterprises. It is not enough to meet the national standards. In the material consumption of the printing process, overprinting accounts for the vast majority. This includes the overprinting of excess consumption due to the process of increasing and decelerating, changing the film roll, etc., as well as the overprinting error consumption caused by other various factors in the normal printing process. Therefore, it is an important research topic for plastic gravure printing companies to effectively reduce printing waste caused by overprint errors. This article tries to make a simple analysis of its influencing factors and discuss it with peers.

First, the basic principle of registration

Due to factors such as the ease of stretching of the printing film and the long printing path, printing errors are constantly generated during the printing process. If it cannot be adjusted in time, it will cause the printing product to be scrapped due to the accumulation of errors. Therefore, it is very important to control overprinting in high and medium-grade flexible packaging gravure printing machines.

In the printing error adjustment method, there are compensation roller adjustment and printing roller phase adjustment in two ways. Most of the traditional plastic flexible packaging gravure printing machines adopt the compensation roller method, while the new independent transmission gravure printing machine eliminates the use of the registration roller compensation phase adjustment method.

The cause and size of the continuous trapping error are all changed. To obtain high trapping accuracy, these errors must be continuously monitored and corrected during the printing process. For low speed printing, corrections can still be controlled manually. It is virtually impossible to do this for modern high-speed printing. Therefore, to improve product quality and production efficiency, register control devices must be used.

The register control system is an important part of the gravure printing press. The main function of the register control system is to track, detect and adjust the overprinting status of the print groups. Register control device mainly consists of photoelectric scanner, lateral register adjustment mechanism, longitudinal register adjustment mechanism and version instrument. The tracking and detection of overprint errors are mainly completed by photoelectric scanners; adjustment of overprint errors is accomplished by the lateral register adjustment mechanism and the longitudinal register adjustment mechanism.

The driving motor changes the length of the printing path or changes the phase of the printing roller by controlling the longitudinal register adjusting mechanism and driving the compensation roller so as to realize the vertical register adjustment. Lateral adjustment adjusts the horizontal relative position of the printing roller based on the detected error.

two. Influence factors of printing registration

In the process of multi-color printing of plastic films, there are many factors that produce trapping errors, mainly in the following three ways:

1. The errors caused by the machinery itself, such as the synchronization error of each printing unit and the accuracy of the printing roller. This type of error is inherent to the machine itself. This kind of error can only be solved by improving the performance of the printing machine and the accuracy of the printing roller.

2. When the plastic film is subjected to the force of stretching, compression, friction, shearing, etc. during the printing process, and various external forces act in various ways, a variety of external forces combine to produce a variety of films. Mechanical effects. Therefore, reducing the influence of these forces on the plastic film and making this effect substantially equal in each printing unit has an important significance for improving the printing accuracy.

3. The third type of error is caused by the following factors: the inherent performance of the film such as the fluctuation of the elastic modulus; the difference of the hot air temperature, air volume, wind speed, etc. in the drying oven; the change of the ink viscosity; the change of the temperature and humidity in the production environment; printing Thin film thickness and elastic changes. Such errors continuously change with time and the amount of deviation is not necessarily a time-varying systematic error.

The influencing factors of the above three types of errors can be divided into equipment, register control devices, process and operating conditions, plate rollers, raw and auxiliary materials and environment, and are described as follows:

1, equipment factors

The overprint accuracy of printed products largely depends on the mechanical manufacturing precision of the machine itself (printer wall plate, traction rollers, guide rollers, etc.) and the technical level of the computer automatic control system used. It directly determines the smooth operation of the machine. Sex. Similarly, a set of printing rollers is difficult to achieve effective registration on one printing press, and can be achieved on another printing press. It is precisely because of this that some companies that manufacture pressboards are reluctant to install their own presses on presses with poor manufacturing accuracy.

In addition to the manufacturing precision of the equipment, the influence of the installation accuracy on the printing register is also very important. For example, the installation precision of the wall plate, the equality of the guide roller, the levelness, etc.

For printing equipment that has been in service for many years, the example of overprinting precision affected by equipment factors is particularly evident. Insufficient maintenance of the equipment can lead to premature wear of equipment, failure of Oldhua or electrical components, etc., which affects the precision of printing registration. Therefore, we must do a good job of daily maintenance of the equipment and regular inspection and maintenance to ensure the normal operation of the equipment.

2, register control device (automatic version of the device)

In the gravure production process, only the register control device works normally to ensure print registration. Any failure in any part of the photoelectric scanner, lateral register adjustment mechanism, longitudinal register adjustment mechanism or control circuit will affect the printing register. This requires that in the event of overprinting inaccuracies, the composition of the register control device must be Partially check and eliminate.

(1) Is the switch connected?
(2) Is the position of the electric eye good? Is there any debris? Is the reflector clean?
(3) Is the Mark's line clear (the color is too shallow to cause electric eye to catch the difficulty)?
(4) Check if the magnetic sensor and fuse are good?
(5)Whether the rearview mirror is dirty?
(6) Is the correct use of the press? Is the version meter working properly?
(7) Is there a mechanical failure in the overprint system?

3, process and operating conditions

(1) Film tension

In the printing process, the range of tension changes is small, and the overlay accuracy is easily controlled. On the contrary, frequent and irregular tension changes will affect the accuracy of registration. Because the change in tension directly affects the elongation of the film. Therefore, the length of the printing path is also changed in different degrees.

The general printing machine tension control system is generally divided into five parts: a feeding section, a feeding section, a printing section, a dispensing section, and a winding section. In doing so, it has a good effect on improving the accuracy of printing registration. It can make the stress conditions of the printing unit films basically the same, the tension on both sides of the film is basically balanced, and second, some tiny variables can be absorbed to reduce the unwinding, The influence of the tension fluctuation of the winding section on the tension of the printing unit of the film keeps the tension of the printing unit stable. Thirdly, the film can be pretreated such as preheating in the feeding section, so that the surface state of the film entering each unit is basically the same.
The influence of the setting of the tension of the commonly used plastic film on the overprint quality during printing is very obvious. Different materials and specifications of the film need to set different tensions, and the tension of each part needs to be adjusted in time when changing the variety. If the tension is too small, lateral overprinting may be inaccurate, and when the tension is too large, the size of the finished product may be shortened.

After setting a reasonable tension, a minimum tension change should be maintained. Unstable tension is mainly caused by failure, damage, or unstable air pressure in the control components of the automatic tension control system. In addition, the factors that cause changes in tension are as follows:

A. Changes in temperature and humidity (changes in the storage environment);
B, the change of the base material with time;
C. Thickness change of the substrate;
D. Changes in speed during operation (caused by acceleration and deceleration processes, unstable motor operation, unstable load changes, etc.);
E. Change in the coefficient of friction of the contact surface between the film and the associated guide roller.