For printed foils, because the actual equipment operating speed is 60 ~ 80m/min, the design speed is generally 100 ~ 150m/min, so equipped with computer automatic register control system in the printing press. The technical indexes of the computer overprint are: the detection accuracy of overprint error is ±0.01mm, the accuracy of overprint is ±0.1mm, the maximum correction range of general overprint error is ±8mm, and the maximum correction range of printing plate deviation is ±9.9mm. Although there is a computer registration system, due to the fact that there are many factors affecting the accuracy of overprinting in the production process, this paper analyzes and discusses the main reasons and treatment methods for the overprinting of aluminum foil inaccurately, and is for reference by those in the industry.
1 Improper overprinting due to incorrect press tension setting
In the foil color printing process, the tension setting of the device setting directly affects the accuracy of overprinting. Therefore, the numerical setting of tension control is a key factor in process control. At present, the aluminum foil overprint tension control system is essentially a special follow-up system in which the input amount changes according to an adjustable attenuation law. Tension control can be said to be the core of the machine. As long as the tension control is stable and the numerical change is small, the color registration accuracy and reject rate of the printing press can be easily controlled. The factors that affect tension fluctuations and changes are often more complicated, but the main factors are roughly as follows: (1) During the process of closing and unwinding aluminum foil on the printing press, the diameter of winding and unwinding aluminum foil is constantly changing, and the change in diameter will inevitably occur. Causes changes in the tension of the aluminum foil tape. When the unwinding torque is constant, the diameter decreases and the tension increases. On the contrary, if the winding torque is constant, the tension will decrease as the winding diameter increases. This is the main factor that causes the aluminum foil tape tension to change. (2) Inhomogeneity of the inner material of aluminum foil. If the material elastic modulus fluctuates, the thickness of the material changes along the width and the length, the mass eccentricity of the material roll, and the change of temperature and humidity in the production environment will all have a subtle influence on the tension fluctuation of the printing press. (3) The reloading of the printing press or the aluminum foil blanking during operation will cause the original stable tension to suddenly change. The higher the speed in the operation of the equipment, the greater the interference. At this time, the tension control system should be able to automatically and randomly adjust the tension according to the tension of the tape tension so that the tension can be restored to the original stable state in time and the accuracy of the overprinting of the aluminum foil can be guaranteed.
2 Incorrect registration in certain parts of the automatic register tracking system
The automatic register tracking system equipped in the equipment is a “neural center†that prints and registers. It analyzes and processes the light signal from the tracking electric eye, and sends the processed control command to each printing color group and the corresponding register motor. On the automatic adjustment of overprint deviation. Failure in one part of the work will cause the register motor to lose control. Such problems should be checked on a link-by-link basis.
3 printing plate manufacturing accuracy impact register
Each plate needs to have a certain manufacturing accuracy, mainly refers to the coaxiality of the plate roller, radial runout, out-of-roundness, and taper of the taper hole of the plate roller. The radial runout of the printing roller has a great influence on overprinting. This is because the printing roller roundness error assembly causes the aluminum foil tension to change irregularly, and changes the length of the entire printing path to varying degrees, resulting in inaccurate overprinting. In addition, the plate cylinder is positioned through its two cone holes, and the taper holes at both ends of the plate cylinder are tightly matched with the two fixed cone heads on the plate shaft. The two fixed cone heads and the key grooves on the two plates The plate cylinder plays the role of axial positioning and radial positioning, respectively. If the deviation of the taper holes at the two ends of the roller is large, the cone head and the taper hole will not cooperate properly, which will affect the running precision of the plate roller, resulting in inaccurate overprinting.
4 The influence of the sensitivity of the printing roller
Many aluminum foil multi-color printing presses use guide rollers and traction rollers to locate and convey the aluminum foil. If the guide roller and the traction roller have poor motion sensitivity, it will cause the aluminum foil tension to change irregularly during the conveying process, thus making the aluminum foil overprint. Not allowed. As the printing machine is running for a long time under working conditions, the equipment itself and external factors will loosen the screws of the guide roller, and the bearing will be easily damaged. At this time, the continuous operation will cause the running resistance of the guide roller to change, and also make the units work in various positions. The change in the length of the print path of the guide roller causes a change in the surface tension of the aluminum foil, which affects the print registration.
5 The influence of color depth and viscosity of printing ink
The depth of the ink color affects the sensitivity of the scanning and tracking of the automatic register system. In the process of printing overprinting, the color of each type of ink is different, and the intensity of the reflected light received by the photoelectric scanning receiving device is not the same, and the pulse height is also different. For example, when the ink is dark, the peak value of the pulse is large, and when the ink is light, the peak value of the pulse is small. In addition, the ink still needs to ensure a certain concentration, not too thin, so as to avoid the color mark during the printing process is easy to "tail". The overprint color mark thus printed is clear in outline, clear in writing, full in color, and accurate in overprinting.
Source: "Printing World"
Author: Bai Bing
Myway Arts & Crafts Co., Ltd. , http://www.pintiehua.com