The concept
On a rotogravure or a flexo press, let us assume that the ready-to-use ink temperature is 25°C and the viscosity is set to 19 (B4) cup seconds. As the printing progresses, the viscosity rises to, let us say, 21 (B4) cup seconds, due to evaporative losses from the ink tray or chamber. Solvent is, therefore, topped-up, to get the viscosity back to the desired 19 (B4) cup seconds.
The print run progresses. All appears fine!
But what’s happening behind the scene?
Quietly and unnoticed, the ink temperature has risen to 30°C, i.e., a rise of 5°C! It is known that the viscosity of the ink must be held at 19 (B4) cup seconds at 25°C to ensure superior quality and consistent shade of printing. Sadly, the ink that is transferred to the web or substrate is at 30°C, so the ink viscosity is different from what it would be at 25°C.
Where has all the additional top-up solvent gone?…… Into thin air!…… Fugitive (evaporative) losses! All due to the rising ink temperature.
Why does the ink heat up?
Ambient temperature does play a role, but that’s just for starters. The temperature of the gravure cylinder or anilox roller rises due to friction caused in the nip, the doctor blade, and the circulation. This is transferred on to the ink in the tray or doctor chamber, resulting in the ink temperature going up.
How do we resolve the issue?
We all know that colour shade is influenced by the ink viscosity. Not to forget that temperature and viscosity too are closely interlinked. Hence, we must maintain the ink temperature to get better control of ink viscosity. To reiterate, we can more effectively control ink viscosity by controlling the temperature.
Benefits of ink temperature control:
• Reduce top-up solvent consumption
• Improve print quality
• Less odour on the shopfloor
• Safer and healthier work area
In the next part, we will explain on how to maintain ink temperature, how the benefits occur, how to overcome operational challenges, etc.
