Flexographic printing pressure

Flexo printing is a lighter pressure direct printing method known as "kiss" printing.

 Since the flexographic printing pressure is very small, the size of the pressure will have a significant change in the quality of the printed product, so the control of the pressure is very important.

Different models have different adjustment methods

Since pressure is the most sensitive issue in flexographic printing presses ( unlike gravure printing, printing quality is not affected by pressure), operators of flexographic printing presses should pay attention to the adjustment of pressure during machine operation. When the general flexographic printing plate is completed, the thickness error of the entire printing plate should be controlled within 0.015mm ~ 0.02mm. The higher the pressure during printing, the more ink is transferred from the printing plate to the substrate. Therefore, in order to ensure that the entire pattern part can be evenly inked, and will not cause hair, paste, etc., the printing pressure, that is, the compression of the printing plate, should be strictly limited within 0.1mm (screen version 0.02mm). If the pressure is too large, the text and images will be crushed, the dots will be deformed and connected to each other, which is prone to problems such as inaccuracy or poor printing on the edge of the pattern. When the flexo plate is compressed by 0.01mm, the embossing force is doubled (1~3kg/cm2), and the increase of the dots of the screen version is serious, which will cause the dark part of the full-page dots to become solid, and the dots will appear hollow dots and dots. Not clean. Due to the change of the dot level, the color cast will be serious, so that the entire picture looks unclear and unclear, the subtle layers cannot come out, and the three-dimensional sense is not strong; if the intermediate layers are too many, the picture will be darker, the color reproduction will be poor, and the Bright color and other problems seriously affect product quality. The solid, line and text have edge effects and hard mouths, the imprint looks uneven, the ink color is not thick, and the text is pasted, so that the characteristics of letterpress printing with strong color and clear peaks are lost.

The size of the dot, which determines the tone reproducibility of the print

According to the principle of geometry, the increase of dots is the uniform expansion of the edge part. For different percentages of dots, the edge increase for each percentage is consistent. For dots with the same area and different shapes, under certain pressure conditions, the dots with larger perimeters have a larger dot expansion rate.

Therefore, the quality of flexographic printing is closely related to the operation adjustment pressure. The size of the printing force should be adjusted to the state where the dots do not expand or the expansion rate is the smallest, and the edge effect and hard mouth are not visible or obvious, which is very important. When adjusting the pressure, the pressure should be zero, and the pressure on both sides should be consistent (balance lines and test strips should be made on both sides of the plate during plate making to ensure that the pressure on both sides of the plate is consistent). The actual printing depends on the specific situation of the layout. For example, when printing a fine screen version, the pressure is relatively small, and when printing a solid version, the pressure is relatively large. In addition, the adjustment of the pressure also includes the adjustment of the contact pressure between the textured surface and the surface of the printing plate. When the pressure between the two is too large, the ink will be squeezed from the surface of the plate to the surrounding of the part with all the pictures and texts, accumulating On the shoulder of the word, a paste plate is formed. At this time, even if the printing pressure is suitable, the dot overlap phenomenon will inevitably appear on the printed product; otherwise, if the pressure between the two is too small, it will affect the transfer of ink. Be sure to use the "plate gauge" (feeler gauge) to carefully adjust before each use - the plate cylinder. Under the condition of ensuring the printing pressure, the pressure between the printing plate and the mesh should be the thickness of the printing plate + the thickness of the double-sided tape - 0.01mm, and the pressure between the printing plate and the substrate should be the thickness of the printing plate + the double-sided tape Thickness + substrate thickness - about 0.01mm to determine the above two pressures. When printing on the ground, it is necessary to avoid excessive printing pressure. Generally, the ghost on the edge cannot be discerned by the naked eye.

Without measuring the version gauge (feeler gauge), the paper [encyclopedia] of the substrate can be sandwiched between the printing plate and the impression cylinder, and then pulled gently, and it can be pulled out after a little force. , basically speaking pressure is more appropriate.

The printing pressure is also related to the printing speed. The printing speed is fast, and the contact time between the printing plate and the substrate is short. The printing pressure should be appropriately increased, otherwise, the printing pressure should be reduced.

The pressure of the anilox mixing and the printing plate is constant (0.02mm ~ 0.03mm), and the pressure of the printing plate mixing and the printing roller is adjustable according to the performance of the substrate.