Eight issues that inks need to pay attention to during flexographic printing
How does the characteristics of the ink determine the amount of fountain solution used?
The fluidity of the ink can affect the amount of dampening solution used in flexographic printing. One of the reasons for using fountain solution in flexographic printing is to make it easier for water to form a water film on the non-printed portion, making it difficult for the ink to spread out to these portions.
Assuming that the ink has a low fluidity, it spreads slowly on the printing plate, and the ink stays in the non-printed portion for a shorter period of time. In this case, we can use a lesser amount of dampening solution; on the contrary, assuming that the fluidity of the ink is large, we should appropriately increase the amount of dampening solution to prevent the ink from sticking to the non-printed portion.
What happens when the ink is emulsified?
If the ink is emulsified, it will produce the following changes:
(1) After emulsification. The water is captured in the ink, occupying the space between its original parts, thus increasing the volume of the ink;
(2) Also, since the water molecules occupy the space of the ink, the proportion of the area occupied by the pigment particles on the surface of the ink is reduced. Since the pigment reflects the color light in the air, and we see the color of the ink, the pigment particles are less, and the ink can reflect less light, which destroys the hue of the ink. Brightness and saturation;
(3) When water penetrates into the ink, its viscosity will also drop.
What is the problem with flexo printing with emulsified ink?
In fact, once the ink is emulsified, its hue. Brightness and saturation are destroyed by the infiltration of water molecules, so the use of these inks for flexographic printing must have a problem of hue shift. Since the saturation of the ink is lowered, the amount of ink has to be increased during flexographic printing, which causes another problem of an increase in the density of the solid.
What is the role of ink viscosity in flexographic printing?
Viscosity can also be called internal friction or cohesion. Physically, its direction of force is opposite to the direction of flow of liquid, and it is a resistance to flow. In the case of ink transfer, the viscosity is generated based on the fact that during the transfer process, the ink layer of the ink is pulled apart, and in order to counter this tension, another inward force occurs, which is the viscosity.
Offset flexographic printing often requires the ink to have a certain viscosity so that the ink has a certain adhesion when spreading on a flat surface to make the dots clear; on the other hand, it can make the surface speed of the ink roller equal, and help the ink to be evenly transmitted. And maintaining a certain thickness of the ink layer.
If the viscosity is too large or too small, what will be the problem?
If the viscosity is too large, the ink transfer is uneven, the paper and paper powder are easily peeled off, and the paper is difficult to peel off from the rubber roller. The flexographic printing quality is greatly affected; and the viscosity is large, the ink spreads on the printing plate. Slow, the ink layer on the plate, after several rotations, the remaining ink layer is not enough to protect the layout, the result will not withstand the pressure of flexographic printing and the role of dampening solution, so that the plate is easy to use. However, if the viscosity is too small, the ink will be too emulsified and dirty, which will make the flexographic printing quality poor.
What is the effect of ink flow?
The relationship between fluidity and viscosity is inversely proportional, the greater the fluidity, the lower the viscosity; the smaller the fluidity, the higher the viscosity. The ink has good fluidity and can guarantee the quality of flexographic printing to a certain extent, because under the same pressure, the ink can spread the ink film of uniform thickness on the surface of the ink roller, and maintain good transfer, making the flexo There will be no uneven prints when printing.
How many drying methods does the ink divide?
In fact, different inks use different methods to dry the ink according to its characteristics and different flexographic printing methods. Generally speaking, the following are not available:
(1) Ink oxidation. This polymeric conjunctiva dry form is the predominant dry form of flexographic printing;
(2) Osmotic drying. When the ink is printed on the paper, its binder will penetrate into the interior of the paper due to the capillary action of the paper fibers;
(3) Play dry. After the ink is printed on the paper, only part of it will penetrate into the paper, but most of it will be played out.
Why do you want to use a drier in the ink?
When the drying ability of the ink material itself is insufficient to meet the time requirement of flexographic printing, we need to add a drier to the ink to speed up the drying. The drier can be combined with the anti-oxidant in the ink to eliminate it and reduce the adverse effects of the anti-oxidant. In addition, the driers can directly absorb the oxygen in the air, making it easier for the ink to obtain the oxygen required for drying and accelerate the oxidative drying.
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