Causes and Solutions of UV Ink Spitting

Jul

1.Understanding UV Ink Spitting
2.Causes for UV ink Spitting
2.1 Factors Affecting UV Ink Spitting
3. Solutions to UV Ink Spitting
4. Conclusion

Understanding UV Ink Spitting

UV Ink spitting during the printing process not only pollutes the environment but also harms the health of operators and hurts product quality. For example, if ink spits onto the surface of the printed matter, it will cause a certain degree of dirt on the surface of the printed matter, affecting the clarity of the printed matter. In severe cases, it will cause the printed matter to be scrapped.

Causes for UV ink Spitting

The reason for the spitting ink is that when the UV ink is transferred, the fiber is cut or stretched at two or more places at the two ink rollers in contact with each other, resulting in fragments, that become spherical due to surface tension. At this time, the double electric layer at the interface between the fiber and the fragment is destroyed, and a part of it remains in the UV ink, and the other part escapes into the atmosphere with the opposite charge. When the fiber shortens, the charge in the printing press will gradually accumulate on the surface of the ink roller and paper, and the fragments, because they have the same charge as the ink, will be repelled into the air when they are close to the ink roller or paper, thus forming spitting ink.

Factors Affecting UV Ink Spitting

Many factors affect the occurrence of ink spitting in the printing production process, such as:

(1) UV ink viscosity
If the viscosity of UV ink is too high, it will be stretched at the outlet of the ink roller, which will easily cause ink spitting.
At the same time, it will also cause uneven ink transfer, paper hair removal, difficulty in peeling paper from the rubber cloth, easy plate flower, plate drop, and other problems;
If the viscosity of UV ink is too low, the ink layer is not well split, which is also easy to cause ink spitting.
At the same time, the ink will emulsify, float, and become dirty, the plate will be smeared, and the dots will be enlarged, thus affecting the printing quality of the printed matter.

(2) UV ink thickness
The thicker the ink layer of UV ink on the ink roller, the greater the probability of ink spitting.
For example, when proofing on coated paper, when the ink layer thickness is required to be 1.2μm, the ink on the plate only needs to reach 2.8g/m2, while when printing on offset paper, the ink on the plate must reach at least 4g/m2.
In addition, once the paper performance is not good for ink adhesion, it will easily cause ink accumulation on the ink roller, resulting in ink spitting.

(3) Ink roller
When the surface of the ink roller is uneven or cracked, part of the ink layer will thicken and the amount of ink mist will increase, which will easily cause ink spitting.

(4) Printing speed
During the production process, if the printing speed increases, the probability of ink spitting will also increase.

(5) Air humidity
If the air humidity in the production workshop is relatively low, it will promote the occurrence of ink spitting;
If the humidity is relatively high, the amount of charge in the air will decrease, and the amount of ink spitting will also decrease accordingly.

(6) Fountain solution
If there is too much fountain solution in the UV ink, serious W/O type emulsified ink will be formed, the viscosity will drop sharply, the ink filaments will become shorter, and serious ink spitting will occur.
At the same time, the fountain solution immersed in the ink will also corrode the metal ink roller, forming a hydrophilic layer on the surface of the ink roller to repel the ink, causing the metal ink roller to deink.

Solutions to UV Ink Spitting

Once the problem of ink spitting is encountered during the production process, the common solutions are:

(1) Adjust the viscosity of UV ink, because different printing speeds of the printing machine adapt to different ink viscosities;
(2) Clean the rubber roller regularly to make the ink layer of the ink roller evenly distributed and improve the ink transfer performance;
(3) Control the printing speed. Too high a printing speed will increase the possibility of ink spitting;
(4) The thicker the ink layer on the ink roller, the greater the probability of ink spitting;
(5) Appropriately increase the air humidity in the production workshop, because when the air humidity is relatively high, the possibility of ink spitting is lower;
(6) Pay attention to the ink-water balance control of the ink during offset printing.

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In short, the ink spitting phenomenon may occur at any time during the printing process due to the contact and rotation of the two rollers. This requires operators to not only have a high level of skills but also be familiar with the data and specifications involved in printing, to minimize the probability of ink spitting.

Conclusion

Generally speaking, the faster the curing speed of UV ink, the higher the surface hardness of the printed ink layer, the lower the flexibility, the worse the adhesion on the surface of the substrate, and the lower the gloss of the printed product.

In short, the various factors that affect the use of UV inks are closely linked and influence each other. Printing companies must consider from multiple angles and eliminate difficult problems in the process of applying UV inks to give full play to the advantages of UV inks.

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