Causes and Solutions for Flying Ink Phenomenon

Posted on 05-06-2024 by

1. Causes of Flying Ink

During ink transfer, when fibers are cut or elongated at two or more points of contact between ink rollers, they form fragments that become spherical due to surface tension. At this point, the double electric layer existing at the interface of fibers and fragments is disrupted. Part of it remains in the ink, while the other part, with an opposite charge, disperses into the atmosphere. As the fibers shorten, the residual charges in the ink gradually accumulate on the surface of the ink roller and paper. Fragments, carrying the same charge as the ink, are repelled into the air when they approach the ink roller or paper, forming flying ink.

Using high-speed machines with viscous ink and low-quality binding materials can easily result in severe flying ink due to the ink being drawn into long threads during the rotation of the ink rollers. Therefore, different models of printing machines need to select corresponding inks to match.

2. Factors Affecting Flying Ink

(1) Excessive ink viscosity leads to ink elongation at the exit of the ink roller, causing flying ink and uneven ink transfer. It also causes paper picking, linting, and difficulty in peeling off the paper from the rubber blanket. Conversely, low viscosity leads to poor ink splitting, also resulting in flying ink, emulsification of ink, dirty printing, plate sticking, enlarged dots, affecting print quality.

(2) The thicker the ink layer on the roller, the more flying ink. For example, on copper plate paper, when the ink layer thickness is 1.2μm, the ink on the plate needs only to reach 2.8g/m2. But for offset paper printing, the ink on the plate needs to be at least 4g/m2. When encountering paper with poor ink adhesion, ink accumulation on the rollers occurs, resulting in flying ink.

(3) Uneven roller surfaces and surface drying and cracking lead to thickening of some ink layers, increasing ink mist and causing flying ink.

(4) Increasing printing speed increases flying ink.

(5) Lower relative air humidity promotes flying ink; higher humidity reduces charges, resulting in less flying ink.

Excessive fountain solution in the ink, forming severe W/O emulsified ink, drastically reduces viscosity, shortening ink threads, leading to severe flying ink. Additionally, the fountain solution immersed in the ink can corrode metal ink rollers, forming a hydrophilic layer on the roller surface, repelling ink and causing ink roller stripping.

(7) Binders in high molecular weight inks tend to draw into long threads during ink splitting, leading to flying ink.

3. Eliminating Flying Ink

(1) Use alcohol-resistant inks to adapt to high-speed printing.

(2) Regularly remove the rubber rollers for thorough cleaning to ensure uniform ink layers and improved ink transfer performance.

(3) Maintain alcohol concentration between 10% and 15%, as too low or too high concentrations are not suitable.

(4) Avoid excessive use of fountain solution, as it shortens ink threads and is detrimental to printing.

(5) Adding electrolytes to the ink reduces flying ink. With the addition of electrolytes, conductivity increases, and the flying ink phenomenon gradually disappears.

In conclusion, the flying ink phenomenon can occur at any time during the printing process due to the rotation and contact of the rollers, which requires operators to not only have high skill levels but also be familiar with the data and specifications involved in printing, minimizing the probability of flying ink occurrence as much as possible.