along with With the continuous development of printing technology, the flexo printing line is no longer rigidly adhered to a single printing method, and it has begun to transform a variety of printing methods that involve multiple printing processes and postpress processing. The installation of gravure printing, screen printing, cold stamping, embossing, die-cutting and other processing methods on a flexographic press now has many successful cases.
Because gravure printing has the advantages of high printing plate durability, long service life, larger ink loading than flexo printing , thicker ink layer than soft printing , and brighter and brighter colors, it is favored by packaging and printing companies. The increase of the gravure printing machine on the flexographic printing machine can be used to realize special printing processes such as gold ink, silver ink, frosted ink, snowflake ink and the like with thicker particles and thicker ink layers. Combined with years of work experience, the author summarizes the precautions of using gravure printing units on flexo presses and is willing to share them with peers.
Printing tension control
Since the printing pressure of the gravure printing unit is much larger than that of the flexographic printing unit, when the two printing methods are used on the same device, the problem that the printing tension of the flexo printing unit does not match the printing tension of the gravure printing unit may arise, resulting in gravure Color group and flexographic group overprinting or overprint fluctuations frequently occur. If the circumferential registration of the gravure printing machine is adjusted, the registration deviation of the flexo printing unit will be more serious. Therefore, how to control the printing pressure in order to maintain the overprinting stability of the printing process and reduce the influence of the gravure circumferential registration adjustment to the flexo printing unit is an important issue that needs to be solved. After continuous exploration, research and practice, the author believes that the following four aspects can be controlled.
(1) Scientifically arrange printing color sequence
Scientific and reasonable arrangements for printing color sequence. Production practice has found that the closer the color group is to the gravure printing unit, the greater the influence of the gravure printing unit on its registration. Therefore, when arranging the printing color sequence, try to place the color with low registration requirements close to the gravure printing unit. Position, keep the color of the registration high away from the gravure printing unit.
(2) Reasonably arrange for idle units
If there are idle units, they should be arranged as close to the front and back of the gravure printing unit as possible.
(3) Reduce the printing pressure of the gravure printing machine
The printing pressure of the gravure printing unit should be minimized to reduce the influence on the printing tension of the flexographic printing unit.
(4) Installation tension control system
A tension control system is installed at the end of the flexographic printing unit so that the tension control during the entire printing process forms a closed loop to maintain the stability of the printing tension.
Practice has proved that the above four methods can significantly improve the printing tension mismatch between gravure printing units and flexographic printing units, effectively solving the problem of registration.
Scraper use
As the saying goes, "open a good gravure printing machine, thanks to a knife." The colleagues who have operated the gravure press know that the correct use of the scraper determines the quality of the gravure and the service life of the gravure. Under normal circumstances, the squeegee mechanism of the gravure printing machine installed on the flexographic printing machine mainly includes: a detachable blade clamping mechanism, a blade angle adjusting mechanism, a blade swaying mechanism, and a blade squeezing pressure mechanism. The specific precautions are as follows.
1. Detachable blade clamp mechanism
The function of the removable blade clamp mechanism is to firmly fix the blade on the blade holder and to facilitate the operator to change the blade. Before installing the scraper, the upper and lower clamps must be thoroughly cleaned. Care must be taken when installing the scraper, and the edge of the scraper must not be damaged. The scraper blade must remain flat on the splint. Tighten the screws on the splint to tighten one by one from the middle to the sides to prevent the scraper from displacing and ensure that the edge of the scraper blade is parallel to the axis of the gravure plate.
2. Scraper angle adjustment mechanism
Scraper angle adjustment mechanism is usually adjusted by a worm gear, and the size of the blade angle directly determines the thickness of the gravure ink layer. Generally, the smaller the angle between the doctor blade and the intaglio plate is, the thicker the ink layer is, but the ink in the intaglio blank space is not easy to be scratched, and the printed product is likely to have the phenomena of knife wire, ink drawing, etc.; the larger the angle between the doctor blade and the intaglio plate, the ink The smaller the layer thickness, the easier the ink in the gravure space is, and the problems such as knife wire and ink drawing are not easy to occur.
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