Differences between ink viscosity and tack

Ink tack and ink viscosity are two distinct properties that describe different aspects of ink behavior in the printing process. Here’s a breakdown of each:

Ink Viscosity

• Definition: Viscosity is a measure of a fluid’s resistance to flow. It describes the internal friction within the ink that resists motion.
• Measurement: Viscosity is usually measured in units like poise (P) or centipoise (cP). It can be determined using devices like viscometers or rheometers.
• Influence: Viscosity affects how ink spreads on a substrate and how well it transfers from the printing plate or cylinder to the paper. Higher viscosity inks are thicker and flow less easily, while lower viscosity inks are thinner and flow more readily.
• Factors: Viscosity is influenced by temperature, solvent content, and the composition of resins and other components in the ink.

Ink Tack

• Definition: Tack refers to the stickiness or adhesion of the ink. It measures the force required to split an ink film between two surfaces.
• Measurement: Tack is typically measured using a tack-o-meter or similar device. The value is usually expressed as a numerical value, representing the force needed to separate two rollers coated with the ink.
• Influence: Tack is important for ensuring good ink transfer and proper adhesion to the substrate. It plays a critical role in multi-color printing, as high tack inks can cause picking or pulling of previously printed layers.
• Factors: Tack is influenced by the type of binders and additives in the ink, as well as environmental factors like temperature and humidity.

Key Differences

• Nature: Viscosity is a bulk property describing flow resistance, while tack is a surface property describing stickiness.
• Role in Printing: Viscosity primarily affects the flow and leveling of ink, while tack affects adhesion and transfer efficiency.
• Measurement: Viscosity is related to the internal resistance to flow, while tack measures the force required to separate two surfaces with the ink between them.

Both properties are critical in determining the printability and performance of inks in various printing processes, and their optimal values can vary depending on the specific application and type of substrate used.