Reducing Sealing Failure
- Published: May 10, 2012, By Tom Bezigian
We discussed his work on package performance and his White Paper entitled "Sure Ways to Reduce Package Failure". The paper can be found at:
http://www2.dupont.com/Packaging_Resins/en_US/assets/downloads/white_papers/Reduce_Package_Sealing_Failure_Barry_Morris_November_2010.pdf
A package has to first and foremost deliver its contents in perfect condition to the end user. It must also run well on packaging equipment, maintain functionality and appearance in the retail environment, and be cost effective. I can tell you from my days at Cryovac, leakers are the bain of a package supplier. Raw material suppliers, equipment suppliers and converters and bagmakers go to great lengths to prevent leakers, which of course result in much waste and cost to the entire value chain. According to information in Barry's White Paper, a 3% increase in leaker rate can result in a 20% package cost, so obviously it is imperative to keep leaker rates as low as possible. His paper specifically addressed three critical areas:
- Consistent seals over a wide temperature range
- An ability to seal difficult packages
- Better package performance
With regard to the first point, there are four polymer attributes that contribute to improved packaging efficiency:
- Wide seal temperature range
- Good hot tack properties
- Low heat seal initiation temperature
- Ability to seal through gussets and wrinkles
Since I was in college way-back-when, we studied ionomer resins and their superior heat seal, hot tack and chemical resistance properties. The graph below, taken from the above referenced paper with permission, shows hot tack strength versus temperature for various common polymers.
Traditional polyethylene resins are not sufficient to provide the protection needed for a wide variety of packaging applications. Newer metallocene polymers offer good strength properties, but over a narrow temperature range. According to Dr. White, zinc-based ionomer resins offer strong heat seals and hot tack strength over a wide temperature range all while offering superior chemical resistance, and the ability to seal through contaminants such as fats.
This last point always impressed me. Most polyethylenes are penetrated by corn oil within 2 days, while most acid copolymers can last 6 days and ionomers can last 11+ days, at which time the test is halted. In my own experience, I have seen ionomers withstand attack from essential oils in tea packaging for more than a year, while standard LDPE resins fail with a day. In dried powder flavored drink packaging, affectionately known as Kool-Aid in the United States, the difference is even more dramatic. I have seen powdered drink formulations flavored with natural essential oils fail immediately on the packaging machine, whereas ionomer resins last nearly indefinitely. I still use these samples in the extrusion coating classes I teach at UMASS-Lowell.
I'd like to thank Dr. Morris for his time. I welcome feedback as well as information from other sources to be included in this blog.
If you are interested in the next class I am teaching on extrusion coating, here is the link:
http://continuinged.uml.edu/plastics/extrusion_coating_technology.htm
I will be in Kuala Lampur next week for a few weeks. If I have internet access, I will blog while I am there.
