Factors affecting plastic gravure overprinting
Abstract: This paper briefly analyzes the basic principles of register printing, process and operating conditions, as well as the influence of printing plate rollers, raw and auxiliary materials and environment on printing register. In the process of plastic gravure printing, inaccurate registration is one of the most common printing faults. The national standard GB7707-87 for printing registration requirements is the main part of the field within 0.5mm, the main part of the level within 0.3mm. Market competition makes the customer's requirements for printing more and more stringent, in fact, there are many live pieces, especially some well-known enterprises' product packaging, only to meet the national standard is far from enough. In the printing process of material consumption, the
Abstract: This paper briefly analyzes the basic principles of register printing, process and operating conditions, as well as the influence of printing plate rollers, raw and auxiliary materials and environment on printing register.
In the process of plastic gravure printing, inaccurate registration is one of the most common printing faults. The national standard GB7707-87 for printing registration requirements is the main part of the field within 0.5mm, the main part of the level within 0.3mm. Market competition makes the customer's requirements for printing more and more stringent, in fact, there are many live pieces, especially some well-known enterprises' product packaging, only to meet the national standard is far from enough. In the printing process of material consumption, overprint inaccuracy accounted for the vast majority. This includes both the process of increasing and decreasing the speed, the replacement of film rolls and other overprint overrun consumption, but also includes the normal printing process of various other factors generated by the overprint error consumption. Therefore, to effectively reduce the printing waste caused by overprinting errors is an important research topic for plastic gravure printing enterprises. This paper tries to make a simple analysis of the influencing factors, and discuss with colleagues.
一、Fundamentals of Arbitrage
Due to factors such as the ease of stretching the printed film and the long printing path, printing errors are constantly generated during the printing process. If it is not adjusted in time, the accumulation of errors will lead to the scrapping of the print. Therefore, overprint control becomes very important in medium- and high-grade gravure printing machines for flexible packaging.
In the way of adjusting printing errors, there are two ways of compensation roller adjustment and plate roller phase adjustment. Most of the traditional plastic flexible packaging gravure presses use the compensation roller method, while the new independent drive gravure presses omit the register compensation roller and use the phase adjustment of the plate roller.
The cause and size of the constant register errors are changing, to get a high register accuracy must be constantly monitored and corrected during the printing process. For low-speed printing, can still use human control to correct. For modern high-speed printing to do this is practically impossible. Therefore, register control devices are necessary to improve product quality and productivity.
The register control system is an important part of a gravure printing press, and its main function is to track, detect and adjust the register of each color group of the print in real time. The register control device is mainly composed of photoelectric scanner, horizontal register adjustment mechanism and vertical register adjustment mechanism and plate aligner. The tracking and detection of register error is mainly done by the photoelectric scanner; the adjustment of register error is done by the transverse register adjustment mechanism and the longitudinal register adjustment mechanism together.
The drive motor controls the longitudinal register adjustment mechanism and drives the compensation roller to change the length of the printing path or change the phase of the plate roller, thus realizing the longitudinal register adjustment. The lateral adjustment is based on the detected error to adjust the lateral relative position of the plate rollers.
二．Influencing factors of printing registration
In the process of multi-color printing on plastic films, there are a variety of factors that produce color errors, mainly the following three:
1, the error caused by the synchronization error of the printing unit machinery and the precision of the plate roller and other mechanical reasons themselves. This type of error is inherent in the machinery itself. This type of error can only be solved by improving the performance of the printing machinery and the method of roller precision.
2, when the plastic film in the printing process by tensile, compression, friction, shear and other forces, as well as a variety of external forces in a variety of different ways, due to the combination of a variety of external forces and the film produced a variety of mechanical effects. Therefore, to reduce the impact of these forces on the plastic film and make this impact in each printing unit is basically equal, for the improvement of printing accuracy is of great significance.
3, the third type of error is caused by the following factors: fluctuations in the intrinsic properties of the film such as elastic modulus; differences in the drying oven hot air temperature, air volume, air speed, etc., changes in ink viscosity, changes in temperature and humidity of the production environment, changes in the thickness and elasticity of the printed film. Such errors change continuously with time and the amount of deviation is not certain, is a time-varying system error.
The above three types of error factors can be divided into equipment, register control devices, process and operating conditions, rollers, raw and auxiliary materials and environment, etc., as follows:
The register accuracy of the print depends to a large extent on the mechanical manufacturing accuracy of the equipment itself (printing machine wall plate, traction roller, guide roller, etc.) and the technical level of the computerized automatic control system used, which directly determines the smoothness of operation. Likewise, a set of plate rollers that are difficult to achieve effective registration on one printing machine can be achieved on another. Because of this, some companies that produce plate-setters are reluctant to install their plate-setters on presses with poor manufacturing accuracy.
In addition to the manufacturing accuracy of the equipment, the impact of the installation accuracy on the printing register is also very important. For example, the installation accuracy of the wall plate, the equality and level of the guide roller, etc.
For printing equipment that has been in service for many years, examples of register accuracy being affected by equipment factors are particularly obvious. Inadequate maintenance of equipment can lead to premature wear and tear, old China or failure of electrical components, etc., affecting the printing register accuracy. Therefore, to do a good job of routine maintenance of equipment and regular inspection, overhaul, to ensure the normal operation of the equipment.
2、Registration control device (automatic plate alignment device)
In the gravure printing production process, only the normal operation of the register control device can ensure the printing register. Failure of the optical scanner, horizontal register adjustment mechanism, vertical register adjustment mechanism or any part of the control circuit will affect the printing register, which requires that each component of the register control device must be checked and eliminated one by one in the event of inaccurate register printing.
(1) Is the switch on?
(2) Is the position of the electric eye good? Is there any debris on it? Is the reflector clean?
(3) Is the marker line clear (too light in color causes difficulty in pouncing on the electric eye)?
(4) Confirm whether the magnetic sensor and fuse are good?
(5) Is the rear view mirror contaminated?
(6) Is the plate aligner used correctly? Is the plate counter working properly?
(7) Is there a mechanical fault in the overprinting system?
3、Process and operating conditions
(1) Film tension
In the printing process, the tension changes in a small range, the overprinting accuracy is easy to control. On the contrary, the tension changes frequently and irregularly, it will affect the register accuracy. Because the change in tension directly affects the elongation of the film. Therefore, it also changes the length of the printing path to varying degrees.
The tension control system of a general printing machine is generally divided into five parts: the feeding part, the feeding part, the printing part, the out-feeding part, and the winding part. This has a good impact on improving the accuracy of the printing register, one can make the printing unit film force situation is basically the same, the basic balance of tension on both sides of the film; two can absorb some small variables, reduce the release, winding part of the tension fluctuations on the film printing unit tension, so that the tension of the printing unit to maintain stability; three in the feeding part of the film can be pre-treated such as preheating, etc., so that The surface state of the film entering each unit is basically the same.
The impact of tension setting on the overprint quality of commonly used plastic films during printing is very obvious, different materials and specifications of films need to set different tensions, and the tension of each part should be adjusted in time when changing varieties. When the tension is too small, it is easy to cause inaccurate lateral overprinting, and when the tension is too large, it is easy to cause problems such as shortening of the finished size.
After setting a reasonable tension, a minimum variation of tension should be maintained. Unstable tension is mainly caused by the failure of the control parts of the automatic tension control system, damage or unstable air pressure. Besides, the factors that cause tension variation are as follows:
A. Changes in temperature and humidity (changes in the storage environment);
B, changes in the warp time of the substrate;
C. Changes in the thinness and thickness of the substrate;
D. Variation of speed during operation (caused by the process of increasing and decreasing, unstable motor operation, unstable change of load, etc.);
E. Changes in the coefficient of friction between the film and the contact surface of the relevant guide roller.