The solution to the problem of dark and light before and after printing

The solution to the problem of dark and light before and after printing

The reasons for the phenomenon of dark and light before and after printing can be roughly divided into three aspects:
1. Changes in the ink volume of the ink roller system

Under normal conditions, every time the ink transfer roller of the ink roller system hits, it basically supplies about 3 sheets of ink, which are stored in the ink path system and released one by one. Once the space of the ink roller system to store these amounts of ink is reduced (for example, the diameter of the ink roller is reduced, the surface area with ink is reduced), the ink flow ink supply will appear.
state shortening. This is like brushing the wall with a brush. When the brush is brand new (with a large ink capacity), once you dip paint from the paint bucket, you can brush out a long ink flow from dark to light; (the ink capacity is reduced), when you can't get too much paint, the ink flow that can produce a consistent color will be shortened
(shade position change). The reduction of the diameter of the ink roller and the shiny state of the surface will affect the amount of ink carried, which in turn affects the length of the ink flow.

2. The relative position of the ink flow of the ink roller and the layout changes

The continuous ink discharge of the ink roller system will generate a series of ink flows from dark to light. When the ink flow contacts the layout, the position of the printing head touching the ink flow is in the middle or rear of the front section, which will cause the layout to be light before inking. The back is deep, the middle is deep and the two ends are shallow, or the difference between the front and the back is shallow. By adjusting the relative position of the layout and the ink flow of the ink roller, a segment with a gentle change in ink color can be selected as the optimal ink supply state.


3. The printing paper expands and contracts, resulting in the change of the ink color of the alternative layout

During the printing process, when the paper is pulled out from the blanket, there is a certain degree of stretching change due to the viscosity of the ink. If this stretching situation is unstable, it will cause the ink on the front seat of the paper to be overprinted on the lower blanket. produce changes, resulting in ghosting of subsequent sheets. Usually, the stretching state will change with the size of the paper. The larger the size, the greater the stretching amplitude, and the change of the back section of the paper will be greater than that of the front section; visually, it will be felt that the back section of the printed sheet has a larger ghost, and the printing color will be lighter than that of the previous section. The front section should be deep; thus there is a phenomenon called front shallow and back deep.

4. The method to solve the problem of dark color before and after printing:

. Check the correct pressure and leveling of the ink/water roller, especially the uneven pressure of the ink transfer roller on the upper and lower rollers
. Improve the condition that the diameter of the ink roller is too small and increase the ink capacity
. Improve the shiny state of the surface of the rubber ink roller and increase the thickness of the ink on the surface of the ink roller
. Adjust the time when the inking roller starts to move to the layout, and change the position of the dark and light colors of the ink
. Check whether the paper is stretched and stretched unstable (observe whether the dots on the back of the paper are ghosted)
. Switch to large corner and small opening ink level printing (change ink distribution state) .
. Check for possible front and rear color deviations caused by afterimages or dents of the blanket (the front part of the blanket is dented, and the back part is normal)
. Change the locking torque of the front or end of the blanket to avoid over-standard locking;
Excessive torque will directly affect the thickness of the blanket