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Commonly specified film attributes
Here are the measurable and quantifiable properties you need to ensure a successful execution of a flexible film package.
A product’s needs for functions – as discussed in the 2012 Flexible Packaging Playbook article, Common flexible packaging performance descriptions – can be described in general terms. However, measurable and quantifiable attributes or properties that relate to these functions are the route to ensuring a film package is successful for a specific application. The types of attributes or properties to consider when determining ‘what matters’ for an end use include (key is to remember that the mix of importance of attributes depends on ‘what matters’):
- Basis weight
- Tensile properties
- Tear strength
- Puncture or impact resistance
- Abrasion resistance
- Maximum and minimum service temperature
- Optical properties
- Heat seal characteristics
- Dimensional stability
- Surface energy
- Coefficient of friction
- Barrier properties
- Chemical resistance
- Regulatory compliance
- Environmental impact
While specific converting sequences and end use applications may have unique requirements or nuances, many similarities exist and taking guidance from rigorously made successful film choices can streamline choosing and specifying. The earlier admonitions are still relevant - knowing why a performance attribute is important (“matters”) leads to better choices and a faster road to new success.
These attributes/properties provide a good starting point, but will not cover all possible end use requirements (think static dissipation for packaging of electronic componentry), bringing us back to the inescapable conclusion that this is a thinking person’s game.
Take care to understand whether an attribute is expressed as an inherent material property that can be extrapolated to different thicknesses or whether the attribute is thickness dependent. Some examples will be highlighted in a table in the article following this one in the Flexible Packaging Playbook.
ASTM International publishes a globally recognized and accepted set of standards for testing many materials, including polymer films; these are the default standards in North America. Given the growth of global supply and trade in films, you will encounter other standards from time to time. International Standards Organization (ISO) and Deutches Institut für Normung (DIN) are examples; where standards published by different organizations are equivalent, the published standards will indicate this. Unless you know for certain, however, it is risky to assume that just because the property name is the same that the results are comparable.
Testing precaution: Compare apples to apples
One caution when reading specifications and comparing properties of different materials is to take care to ensure the data are presented in such a way as to allow valid comparisons. Start by being sure you know exactly what property is being reported. Then recognize there are differences in how these properties can be measured and reported. Make sure you understand the specifics of
- The test method employed,
- The conditions at which testing was done (same method at different temperature, humidity, etc.) can yield wide variation), and
- The units in which the results are reported.
Units can be converted relatively easily, but the impact of varying test conditions on results can differ by material and it is dangerous to expect all materials to respond similarly. Finally, minor and major differences in test methods can influence results.
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The author specializes in flexible packaging, and has spent 30 years leading package development at several prominent packaging converters.
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