Tack and viscosity are two different parameters of the offset ink. Tack refers to the resistance to separating the ink layer. Viscosity describes the resistance to flow and deformation during operation. Do not use these names interchangeably.
What does offset ink tack mean?
An ink film splits when surfaces come into contact and subsequently separate. “Tack” describes the ink’s behavior during this process; it is a key factor in ink transfer and how the ink interacts with the paper surface.
If the ink’s tack is too high relative to the substrate’s surface strength, it may cause fibers or coating particles to be pulled away (picking). However, this does not mean that every instance of paper dusting requires a reduction in tack. First, examine the substrate, the condition of the printing blanket, and the operating conditions.
What does offset ink viscosity mean?
Viscosity helps describe how an ink flows and performs within the inking system. Offset ink is a material with complex behavioral characteristics; both temperature and shear conditions influence measurement results.
Do not compare two values without knowing the measurement method and temperature used. While assessing an ink with a spatula can help identify changes, it is not a substitute for a standardized, comparable measurement.
Tack and viscosity: a simple comparison
| Parameter | What does it describe? | What should you look out for? |
|---|---|---|
| Tack | Ink layer separation resistance. | Substrate surface transfer and strength. |
| Viscosity | Flow and deformation resistance. | Measurement conditions and ink operation in the system. |
The parameters may change together, but they are not the same thing. You cannot calculate the tack based solely on viscosity. Warming up the system can change both parameters, so take temperature into account when diagnosing.
How to choose ink for the substrate?
Tell us the type of paper or cardboard, technology and description of the problem. Add printing speed and whether the defect appears after the machine warms up. At WIT, we will help you choose sheetfed offset process inks …for a specific job.
Do not attempt to modify an ink by adding an arbitrary oil. Such an additive can alter multiple parameters simultaneously. If an adjustment is necessary, consult with your supplier regarding the appropriate product and dosage for that specific ink.
Does a lower tack always help?
No. The choice depends on the substrate, the transfer characteristics, and the entire printing process. Excessive adjustment can negatively affect other ink properties. Always identify the root cause first, and verify any changes through a test run.
If the issue involves water content, please also refer to the entry: emulsifying the offset ink.
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