Both flexographic printing and letterpress printing are in the form of letterpress printing. In order to facilitate understanding and differentiation, it is customary to use liquid ink and soft printing plates as flexographic printing. Traditionally, paste inks will be used. The printing method of hard plates is called letterpress printing. This article only briefly introduces the "difference between flexo and letterpress printing" in several aspects.
First, the principle of printing ink
The relief printing apparatus transfers the uniform, very thin ink layer in a unitary form to the surface of the printing plate by one or several inking rollers, and then performs printing. The flexographic plate is made by a metal anilox roller that is in contact with the printing plate to transfer ink. The specification of the net stick is fixed, so the amount of ink transfer is also fixed. The ink is stored in the cell space before the transfer. Because the mesh wall in the cell is very thin, during the transfer process, the ink in the cell is quickly leveled and the ink layer on the plate is formed integrally when the ink is in contact with the plate. Finally, printing.
The two are different in the principle of ink. The letterpress is a soft glue stick that is in contact with a hard plate. The thickness of the ink layer changes the amount of ink. The flexographic plate is a hard metal anilox roll that is in contact with a soft plate. The size of the stick changes the amount of ink.
Second, printing ink
According to the principle of printing ink, the letterpress printing ink is transferred to the printing plate in a monolithic film shape, which requires a certain strength and coupling force between the inks, otherwise the ink cannot form an ink film and is normally transferred, so the letterpress ink has a certain viscosity. Paste ink.
The transfer of flexographic printing ink relies on the rapid outflow and leveling of the ink from the cell, requiring the flexographic ink to have a low viscosity and a fast transfer speed, so the flexographic printing ink is a low viscosity, fluid liquid ink.
Third, the inking system
In order to evenly transfer the paste ink onto the printing plate, the letterpress printing machine has a complicated inking system, including; ink fountain, ink fountain roller, ink transfer roller, ink transfer roller, ink roller, ink roller, etc., called long ink. Road system. Only through the long ink system, the paste ink can form a uniform ink layer.
Flexographic printing uses liquid inks, eliminating the need for complex inking systems, requiring only one ink fountain roller to transfer ink to the mesh stick or to directly contact the screen stick with the ink (gravure inking method), the surface of the net stick The ink is finally removed by the squeegee and the ink is stored in the cell. This type of ink transfer is called a short ink path system. The short ink path system is simple, easy to adjust, and low in material consumption, which is the biggest feature of flexographic printing.
Fourth, the adjustment of ink volume
There are usually two ways to adjust the amount of ink in letterpress printing;
1. Adjustment of the overall ink volume:
(1) Adjust the rotation angle or speed of the ink fountain roller to change the ink transfer amount of the ink fountain roller.
(2) Adjust the swing frequency of the transfer roller to increase or decrease the contact time with the ink fountain roller, thereby changing the ink transfer amount of the system.
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