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.