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Seal Integrity: A Primer from a Pro

A provider of engineered solutions for the food and beverage industry for more than 40 years, Mark Green of Mark Green & Associates shares some thoughts on seal integrity testing.

Mark Green Fp

Packaging World:
What’s the big-picture view of product freshness and the role played by package seal integrity?

Mark Green:
Every manufacturer of food product faces the challenge of maintaining stability or “freshness” throughout the shelf life of their product. Significant investments are made in product and process design to maximize this time including producing and maintaining hermetically sealed containers. A failure to achieve package integrity typically results in spoilage and/or reduced product performance over time. For highly sensitive products, the manufacturer is faced with a potential product recall, reduction in brand equity, and lost consumer confidence.

Why not just design quality in, so that there is no need for testing?
I have long been a proponent of designing quality in as opposed to testing it out. The objective is to develop a combination of package components and closing/sealing processes to produce consistently robust packages. Having personally participated in development and validation of multiple types of these package systems, I can attest to countless hours of producing and testing samples to achieve the optimal design. Despite our best efforts in specification development and standard operating procedures, invariably at some point packages will be produced with compromised seals.

Is there any single biggest challenge facing food manufacturers in this area?
The biggest challenge we face in manufacturing is to detect the seal failures in “real time” to allow production to stop and correct the cause before producing a warehouse full of suspect product, or worse, releasing the product for distribution. Obviously, for this to be possible, the leak detection method must be non-destructive. Multiple non-destructive approaches to 100% on-line leak testing exist, but their effectiveness is limited depending on the line speed and cycle time for the leak testing. For example, a line producing 30 units/min could test 100% of production if the test cycle time is two seconds or less. Doubling the line speed to 60 units/min will cut the test cycle to 1 second or less and so on. With all types of leak testing available there is an inverse relationship between cycle time and size of leak that can be detected. Highly sensitive products generally require testing down to the equivalent of at least a 20-micron hole. The fastest known cycle time available today for this limit of detectability is five seconds. It is possible to install multiple testing units and split the production stream across them, but this is costly and requires a larger footprint.

Presumably there are times when 100% testing is not practical, yes?
Yes, and when that’s the case, a food manufacturer must still be able to develop an effective quality control program for seal integrity. Most manufacturing projects I have worked on ran at line speeds exceeding 200 units per minute, requiring us to utilize a less than 100% testing approach. Generally, the strategy is to test key package quality attributes and leak test from a statistically significant sample of the product stream. Since the package and process variables are unlikely to vary greatly over the relatively short intervals between tests, this strategy has been shown to be effective in minimizing leak integrity issues.

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