Blocking is the unwanted adhesion between layers of plastic film. Results reflect the ability of a material to adhere to itself when pulled apart. ASTM D3354 specifications are used to program MAP-4 materials testing software to run the blocking test. The results demonstrate the degree of blocking that exists as a result of factors including film processing, storage, temperature and pressure.
To measure the blocking load of a plastic film by the parallel plate method, the Thwing-Albert Vantage Series Tensile Testers with MAP-4 software can be used to quickly analyze the data collected from the test.
The method can be summarized:
- Using two plastic blocks the two layers of film are pressed between them
- One layer of film is attached to the upper block and the other layer is attached to the lower block
- The upper and lower block are slowly separated
- The film layers are then pulled apart at a constant speed until separated
- The force to separate the layers of film is recorded in realtime