Blocking - What is blocking?
Blocking is surface to surface sticking between sheets or rolls of labels, which involves either the adhesives, coatings, or print used to create those labels (or a combination of these elements). It is caused by pressure, heat, improper drying, or improper curing (depending on the elements involved) and may be prevented by careful storage and processing of label products during manufacturing, storage and distribution, and printing.
If an adhesive is exposed to heat or pressure it may begin to flow or ooze out of place; when a label is stored in “normal conditions”, this is referred to as “cold flow”. In these cases, the adhesive may begin to spread from between the face material and backing sheet onto any adjacent surface; this will result in a sheet of labels sticking to any nearby surfaces (such as an adjacent sheet in a stack of sheets) or layers within a roll of labels sticking together. Adhesives that rely on the presence of a specific substance to activate or cure the adhesive may also result in blocking if that substance is introduced accidentally, too early in the manufacturing process, or in too high a quantity. For example, if a water sensitive adhesive is exposed to water too early or accidentally, it will activate and adhere to any nearby surface.
Coatings may behave similarly when exposed to heat and/or pressure. Coatings are also liable to cause blocking if they are improperly dried or cured; if a coating on a label comes into contact with another surface before it has dried or cured in place then it is likely to stick to that surface. The same effect occurs when print doesn’t dry or cure completely before coming into contact with another surface – this is known as set-off. For example, if sheets of labels are printed and stacked on top of one another very quickly, the print may not have time to dry properly and would adhere to the back of the sheet above it.Go Back to Glossary