Causes of blocking include residual solvents, plasticizers, and static which can promote adhesion between flexible packaging materials,
ASTM D3354 quantifies the degree of blocking (unwanted adhesion) between layers of plastic film. It is not intended to measure susceptibility to blocking. The blocked sample is adhered between two compression plates and the force to separate the films determined.
ASTM D918 determines the blocking resistance of flexible types of packaging materials, including the following:
- Impregnated, coated or laminated papers
- Coated and laminated metallic foils
- Polymer films and plastic laminates
The test method provides a range of standard conditions of temperature and relative humidity at constant pressure for a specified time which is designed to simulate varying climatic conditions that may be encountered in the manufacture, storage, transportation, or use of the materials. A simple subjective three-level assessment is made: no block, some block or well blocked.