Gravure printing cylinder

The gravure embossing cylinder is a rubber coated metal cylinder that is driven by friction and presses the substrate toward the plate cylinder. The role of the impression roller is:
1) Obtain a suitable ink transfer effect;
2) Adjust the tension of the web between printing units;
3) Drive and guide the web through the press.
The contact line between the impression cylinder, the web and the plate cylinder is called a nip. The impression cylinder is not driven by the printer but is driven by friction.
The pressure of the nip line is usually between 50 and 200 PLI (the roll is between 50 and 100). The outer layer of the impression cylinder is surrounded by rubber or elastic polymer. The ink in the plate cylinder is pulled out by the combination of embossing and capillary action. This process can also be electrostatically assisted. We will discuss this later. The rotation speeds of the impression cylinder and the printing cylinder are different because their radii are not the same.
Due to the elastic properties, the rotation of the impression cylinder is not uniform; due to the pressure, the local rotation speed at the nip line will decrease. The elastic extension of the roller surface at the embossing point causes this phenomenon. The general principle is to keep printing pressure to a minimum while ensuring acceptable print quality. Increasing the printing pressure will tend to stretch the web and the plate cylinder more tightly, and the possibility of close contact of each ink storage cavity with the substrate will increase.
However, an increase in printing pressure also increases the surface pressure of the printing machine, the pillow, the web, and the impression cylinder. Moreover, the high pressure causes the gravure deformation of the rollers and rollers to increase, resulting in heat generation in the cladding layer. The effect of these factors in turn determines the print quality, printability, and drum (roll) life. The major printing failure in gravure printing is the inability to transfer ink from each cell to the web.
As a result, there are "snow spots," "lost dots," or "matches." These phenomena are mainly caused by rough and uneven surface of the substrate. Therefore, the printing quality of the copper paper (coating) or super gloss paper is better. Electrostatic Assist (ESA) is developed to improve the transfer of inks to substrates. The ESA constructs an electric field in the plate cylinder and the impression cylinder. This has a special effect on charged or polar pigment particles in the ink.
This treatment is effective for polar or non-polar solvents. Compared with other methods, ESA contributes significantly to the improvement of gravure quality:
1) It improves the printing effect of a wide range of substrates;
2) Reduced waste;
3) Reduced printing pressure;
4) Increased printing speed;
5) Reduce the build-up heat of the impression cylinder;
6) The service life of the impression cylinder is extended.
In the absence of ESA, the ink will wet the plate and form a concave meniscus shape in the cell. With the application of an electric field, the movement of charged or polar particles destroys the concave surface and pulls it out of the cell; thus reducing the wetting of the ink against the cell wall. The negatively charged pigment particles are attracted by the positive electrode on the impression cylinder and the negative electrode on the plate cylinder, so that the ink is transferred from the cell site to the surface of the substrate. The voltage of the electric field is 500-1000 volts, and an electric field of 4-6 x 106 volts/meter is formed on the coil thickness.