Flexo Printing Series Lecture 1

Talent is the most indispensable for a company. Compared to the rapid development of flexographic printing in China, the shortage of professional technicians in flexographic printing is particularly prominent. In order to help the flexographic printing industry develop more suitable talents, the magazine invited industry expert Cai Chengji to start a series of flexographic printing technology lectures. At the same time, it also hopes that the colleagues interested in flexographic printing will participate in it and jointly promote the healthy development of flexographic printing in China.

1. What are the main components of a satellite flexographic printing press?

The main components of the satellite flexo printing press are:

(1) Central impression cylinder and various printing units. The fundamental difference between a satellite flexographic printing press and a 100-unit flexographic printing press is that each printing unit shares a central impression cylinder, and the printing units are distributed around the central impression cylinder. When the printing substrate is pressed against the impression cylinder for one week, multi-color printing of each color group is completed.

(2) Unwinding and unwinding the roll device. The retracting and retracting device of the satellite type flexographic printing press generally adopts a DC motor soft connection. Both the unwinding device and the rewinding device form a closed-loop control system. The floating roller tension detecting device detects the tension of the unwinding or rewinding and sets the value thereof. Feedback to the computer controller, the speed adjustment by the DC motor, the tension of each closed-loop system is constant at the set value. The unwinding and rewinding parts are generally used to change the roll without shutting down, in order to reduce the loss of raw materials, and minimize the decrease in capacity when changing the roll.

(3) Drying device. The drying device of a satellite type flexographic printing press is generally divided into two parts. One is a color set inter-drier disposed between printing units, and the other is a bridge drier completed after each color set is printed. The dryer is installed between each color group between adjacent two color groups. For example, the first color group dryer is installed between the first and the second printing units. Its role is to ensure that the flexographic printing machine is wet and wet during the printing process. According to the needs of the process, after the dryer dries the ink, the surface of the ink has been formed into a film, but not a thousand: transparent. Therefore, the N-color softness printing press needs to be equipped with a N-color inter-group dryer. After the printing of the last set of printing units is completed, there is no longer any need for overprinting. Therefore, such dryers are generally not added directly into the bridge dryer. The bridge dryer is actually a bake tunnel designed according to a certain length. Since it is located between the central impression cylinder and the winding device, it looks like a bridge connecting these two components.

(4) Printed substrate cooling device. The printed materials dried by the bridge drier need to be cooled before winding. Because the general production speed of the satellite type flexographic printing machine is above 250m/min, the air-cooling under natural conditions can not meet the requirements of the substrate. Radiating heat, therefore, cooling is enhanced by a chill roll with a built-in water circulation system. The surface of the chill roll is chrome-plated to prevent condensation of cooling water from corroding the surface of the roll:

(5) Edge control device for printing substrates. The device is installed in the unwinding and winding section to ensure that the transverse (end face) surface of the printed substrate is neat and tidy.

2. What are the characteristics of the central impression cylinder of a satellite flexographic printing press?

The central impression cylinder is the core component of the satellite flexographic printing press. The roller is a double-layer structure casting with built-in water circulation system. The roller surface is processed with precision technology and the radial runout error of the roller is strictly controlled. Generally, the roller is controlled within ±0.01mm. Foreign manufacturers of satellite-type flexographic printing presses do not all have the ability to process central impression cylinders. Many companies have commissioned professional manufacturing companies to process them, and there are also differences in manufacturing precision among companies. The larger the cylinder diameter, the more difficult the error control becomes. Big. The surface of the impression cylinder is treated with a plating layer. The quality of the treatment layer directly affects the corrosion of the condensed water on the surface of the cylinder. The built-in water circulation of the central impression cylinder is not just a cooling system. It is also a constant temperature control system with a control accuracy of ±0.6°C. The role of this system is to control the expansion of the metal body in the direction of the diameter of the drum. In the normal printing process, since the printing units are wrapped around the central impression cylinder, the printing substrate is closely attached to the surface of the central impression cylinder, and a color-group dryer is installed between adjacent printing units. Whether it is drying with hot air or drying with UV will generate a large amount of heat. This heat is transferred to the surface of the drum, which will inevitably cause the surface temperature of the drum to rise, which will cause the expansion of the metal body and cause the radial runout error of the drum to increase. In this sense, the built-in water circulation system is mainly a cooling system. However, due to changes in the ambient temperature around the printing press, the use of heating in the winter is also taken into account in the refrigerating of circulating water, so the system is often equipped with a heating device. After setting the basic value of temperature control, using temperature detection, adopt P. 1. D control mode to adjust the constant temperature of the circulating water. The main pressure source of the central impression cylinder thermostat and the satellite type flexographic printing press is often divided into power supplies. When the host computer is turned off, the thermostatic control device cannot be turned off and must be kept powered for a long time. If for any other reason the thermostat must be powered off, after the power is turned on again, the central impression cylinder must be turned on and kept warm for 4 to 8 hours. If the production time is not allowed, it must be kept at least 2 hours.

3. Why do we have to regularly measure the quality of water in the central impression cylinder?

Manufacturers of satellite flexographic printing presses are often obliged to stipulate the annual water quality of the water circulatory system when formulating maintenance and service manuals. The main item of measurement is iron ion concentration, etc. This is mainly for monitoring the scale generation in the pipeline. Once scale is formed on the inner wall of the central impression cylinder, the thermal conductivity will change, and the entire temperature control system will not guarantee the control accuracy. When the water quality exceeds the specified standard, the user of the flexographic printing press must use water treatment methods to restore the circulating water quality to normal values.

4. How to detect the radial runout of the central impression cylinder?

The method of detecting the radial runout error of the central impression cylinder is as follows:

(1) A metal roller is installed at the position of the mounting roller to replace the air expansion shaft of the conventional roller.

(2) On the surface of the metal roller, there is a dry sub-table with a magnetic base, and the magnetic base is directly adsorbed on the roller surface.

(3) Lightly touch the contacts of the dry table on the surface of the central impression cylinder and adjust it to zero.
(4) Rotate the central impression cylinder one revolution to observe the maximum value of the rotation of the dry pointer hand.

(5) A 5-point test is performed on the entire width of the web to determine the radial runout error of the surface of the central impression cylinder.

5. How to calibrate the excessive radial runout error of the central impression cylinder?

There are two commonly used methods, one is to adjust the water quality according to the water quality test data, then increase the water temperature, use the metal body expansion characteristics to achieve the purpose of calibration. Temperature control system commonly used setting is 30 °C, some equipment only uses 25 °C, different manufacturer's central drum temperature set value is generally different, if possible, increase some temperature, will be able to improve its radial runout error Increase. Another solution is to calibrate the balance adjustment device inside the drum directly. This method is not available for every kind of equipment. There are holes in the side walls of the central drum of the equipment that allow people to enter. There are radial adjustment mechanisms inside, and people can drill into the central drum to adjust. If the device does not have an adjustment mechanism and there are no more channels that allow people to enter, this method cannot be used.

6. What are the characteristics of the printing unit of a satellite flexographic printing press?

The anilox roller, plate roller, and common central impression cylinder of a satellite flexographic printing press constitute a typical flexographic three-roll system. The three-roll system of the unit type flexographic printing press is generally centered on the printing roller. The anilox roller and the impression roller are arranged on both sides to form an isosceles triangular structure. When the relative position of the three rollers is adjusted, the upper and lower positions of the roller are mainly adjusted, and the front and rear positions of the plate roller may also be slightly adjusted, but the amplitude is small. Since the diameter of the anilox roller and the impression cylinder are similar when adjusting the printing roller, the inking pressure of the printing roller on the anilox roller and the printing pressure of the printing roller on the printing roller have some implications. The three rollers of a satellite flexographic printing press are completely different. The anilox roller and plate roller are installed side by side on a single platform and form a complete printing unit with a common central impression cylinder. The anilox roller and the plate roller can be independently adjusted, and the inking pressure and the printing pressure are not related to each other and are not implicated. Taking the manual adjustment of the three rollers as an example, the operator first adjusts the pressure of the anilox roller to the plate roller, adjusts the distance between the two in the direction of the adjustment screw, and the anilox roller leans toward the plate roller until the plate is completely inked. . Secondly, adjust the distance between the printing roller and the impression roller, observe the increase of the dots in the printed sample, and fine-tune the gap between the two rollers as appropriate to minimize the dot gain. Finally, fine-tune the anilox roller again, because the visual inspection of the anilox roller for the first time is based on whether the printing plate is completely inked. Therefore, in general, the pressure is always too large. At this time, the anilox roller will be the same as the roller. Increase the gap, as long as you keep the ink on the plate. In this way, it can be determined that the three-roll adjustment is basically in place and the relative position of the three rollers can be locked.

Author: United Printing Equipment Co., Ltd. Cai Chengji (Cai Chengji teacher was in Shanghai People's printing plant, Shanghai Zi Quan Packaging Co., Ltd., Tiger Packaging (Shanghai) Co., Ltd., Shanghai Zihua Enterprise Co., Ltd. and other enterprises engaged in production and technology management , has long been engaged in flexible packaging printing, compounding and filming work, familiar with gravure printing and flexographic printing processes, contacted flexographic printing since the mid 1980s, and successively operated flexographic printing equipment manufactured in Germany, Italy, and other countries, in production practice In the process, it has explored a set of practical and flexible flexographic printing technologies and brought out a group of young engineering and technical personnel who understand the theory and practice, and has served as the first and second member of the Professional Printing Committee of the Printing Association of China Printing Association, and the packaging and printing of the China Association for Packaging. A member of the committee's expert group, a newly established director of the Printing Association's Flexo Printing branch, is currently the director of product technology for United Printing Equipment Co., Ltd.

Source of information: printing and packaging. decorating technology