Viscosity - What is viscosity?

Answer:

A measure of a fluid's resistance to flow caused by internal friction between neighbouring particles as a fluid is moving. Viscosity depends on the size and shape of a fluid's particles and the attraction between the particles (as well as any attraction between the particles and any surface a fluid touches). A highly viscous fluid will have greater adhesion (attraction between fluid particles and surface particles) and cohesion (attraction between fluid particles); this means that the particles remain closer together and therefore flow slowly. A less viscous fluid has weaker adhesion and cohesion, allowing the particles to spread farther apart, and so flow faster.

In label production and printing, viscosity encompasses a substance's quality of tack (the ability to adhere quickly to a surface) and flow (the ability to spread across a surface). This is particularly important for coatings, adhesive coatings, release coatings, and printing inks, all of which must be able to flow when they are applied to a surface and then adhere to that surface to remain in place.