Viscosity, often referred to as ink consistency, is a critical property in flexographic printing that significantly impacts the quality of the final printed product.
In this article, we'll explore the role of viscosity in the production of high-quality flexo prints, its measurement, and its impact on various aspects of the printing process.
Understanding Viscosity
Viscosity is the property of an ink that determines how it flows and transfers from the ink fountain to the printing substrate.
Think of it as the ink's thickness or consistency.
Maintaining the right viscosity is crucial for achieving consistent, uniform, and high-quality prints.
Factors Affecting Ink Distribution
In flexographic printing, ink distribution depends on several factors, including the anilox roll's engraved surface, the fountain roller's hardness and pressure, doctor blade systems, press speed, and most importantly, ink viscosity.
When these factors are constant, any significant variations in ink film thickness or density are typically due to changes in ink viscosity.
The Impact of Viscosity
Too Viscous Ink: If ink is too thick (high viscosity), it results in heavy ink film thickness, causing color deviations, dirty printing, and type filling in.
This leads to prints that are off standard and unacceptable.
Too Thin Ink: Conversely, if the ink is too thin (low viscosity), it results in a washed-out appearance, leading to equally unacceptable prints.
Variations in Viscosity: Fluctuations in viscosity throughout a print run can cause prints to lack uniformity, resulting in intermittently too light and too dark sections.
Yield Value of a Liquid
Viscosity is not a one-size-fits-all concept. Some liquids have a yield value, which means they won't flow until a certain force is applied.
Understanding this property is essential, as it influences ink behavior during the printing process.
Importance of Viscosity Control
The early adoption of automatic viscosity control systems in flexographic printing was met with skepticism due to the perceived cost.
However, as the industry evolved and demands for higher quality prints increased, the value of these systems became evident.
Automatic Viscosity Control Benefits
Reduced ink consumption: Automatic control systems can significantly reduce ink wastage, leading to cost savings.
Improved print quality: Consistent viscosity ensures uniform print quality and color accuracy.
Increased press speeds: With automated viscosity control, press speeds can be increased, leading to higher productivity.
Conclusion
Viscosity is a critical parameter in flexographic printing , affecting ink distribution, print quality, and production efficiency.
The adoption of automatic viscosity control systems has become essential for consistently producing high-quality flexo prints.
As the industry continues to evolve, understanding and managing ink viscosity remains a fundamental aspect of successful flexographic printing.