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Cause offset printing press color phenomenon

Usually the printing factory for two-color or multi-color offset presses, color mixing often occurs in book printing, and the reasons are as follows.

For a two-color or multi-color machine, the overprinting method is generally a wet-stack type, unlike the wet-stacking method of a monochrome machine. Typical ink fixing speeds are ten minutes or longer. In the case of multi-color machine, the gap time between two colors is only about 1 second. In such a short time, it is absolutely impossible to completely fix the imprinting ink on the paper surface, which is the basis of the color mixing phenomenon.

1, the effect of the viscosity of the ink of each color group

Generally, the ink color sequence arrangement should be arranged in the order of viscosity from high to low to prevent the latter color ink from adsorbing the previous color ink. However, when the manuscript is limited, the original color is required to be biased toward the ink, for example, cyan. When the color sequence is arranged, the cyan color should be printed. In this case, the cyan viscosity should be considered too large, and a certain amount of detacking agent should be added to the ink. In order to reduce its viscosity, prevent the occurrence of color mixing.

2, the effect of ink depth and coloration rate

Generally, the coloring rate of domestic inks in actual production is lower than the standard coloring rate index. To achieve the same solid density value in printing, it is necessary to increase the amount of ink, that is, increase the thickness of the ink. When the ink is not dried, the thicker the ink layer, the more easily it is broken by the external force (printing pressure), and the color mixing phenomenon is likely to occur.

3, the impact of ink drying performance

In the actual production, the early drying of the ink is serious, and the sky blue ink is particularly noticed here. When the machine is running, the rubber roller gradually heats up, especially in the summer. The ink starts to change on the rubber roller, and the viscosity gradually increases, which is more serious after transfer to the blanket. This often causes color mixing. For example, when the J2205 machine prints red or green, the printing is normal, but when printing a certain number (several thousand), carefully observe that the magenta ink gradually darkens. To solve this problem, the operator needs to master the drying performance of the ink.

4, must pay attention to ink and water balance when printing

If the ink balance is out of control, it will cause "water" and "ink" to be large, and the ink staying on the ink roller will increase accordingly, which is equivalent to increasing the diameter of the ink roller, increasing the pressure between the rollers, and making the ink roller hotter and hotter. The easier it is to dry, the viscosity of the ink increases accordingly, resulting in a series of vicious cycles, which can easily cause color mixing.

5, do a good job of cleaning the layout

When printing in factory, it is necessary to level the pressure of the water and the ink roller, and pay attention to the pH value of the fountain solution to prevent the dirty plates on both sides of the plate. If the blank portions on both sides are dirty, transfer to the blanket and the impression cylinder, and then transfer to another group of ink rollers, it will also cause color mixing. In addition, when the plate is made, the signal strip and the color mark are also printed on the plate. When the printing is normal, it can be removed to prevent color mixing.

Release Date: 05-04-2019 15:05:25 [Go back Menu]

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