The shear strength of a pressure sensitive label or tape can be used as a guide to the resistance to adhesive bleed. Adhesive bleed is the "oozing" of adhesive beyond the perimeter of the face material. Adhesive bleed usually associated with heavy coat weight adhesives or adhesives with low temperature flow.
For determing adhesive resistance to shear, test pieces are applied to the specified area of a 'standard' substrate test plate such as float glass, stainless steel or other surface of interest using a rubber covered roller.
Smithers Pira clamp the test plate in a ChemInstruments 8 Bank Shear Tester set at a 2 angle, with a weight (usually 1kg) attached to the free end of the test piece.
The time taken for the test strip to adhesively shear from the test plate is automatically recorded. The tests can be run within a temperature controlled chamber to assess heat resistance.
Smithers Pira shear adhesion tests include:
- FINAT test method 8, for pressure sensitive labels
- ASTM D3645, for pressure sensitive tapes
- PSTC 107 for pressure sensitive tapes