Assessing Real-Life Sealant Performance in Flexible Packaging

Published: October 01, 2000, By Jeffrey J. Wooster & Laura K. Mergenhagen, The Dow Chemical Co., Freeport, TX

Application: Polyolefin plastomers exhibit excellent caulkability to deliver the sealing characteristics necessary for total package performance.

The most important function of a sealant is to maintain the complete integrity of a package. In doing this, the sealant maintains the proper environment inside the package. Determining the ability of various sealants to maintain package integrity is not simply a matter of measuring heat seal strength, hot tack strength, or initiation temperature. Although laboratory testing is a valuable means to compare sealants, it does not tell the entire story. Traditional heat seal and hot tack testing do not measure the ability to seal completely through the folds, contaminants, and wrinkles that occur in an actual packaging environment. Testing the integrity of flexible packages allows better prediction of "real-life" performance because it characterizes the "caulkability" of a sealant resin.

Single-site catalysts have revolutionized the design, manufacture, and use of polyolefins in flexible packaging applications. New catalyst and process technologies permit the commercial manufacture of polyolefin plastomer (POP) resins with narrow molecular weight distributions and short chain branching distributions. The POP materials offer desirable performance benefits when used in mono-layer or multi-layer packaging films—outstanding sealability, excellent optics, low extractables, minimal contribution to off-taste and off-odor, high impact strength, high puncture resistance, and high permeability to oxygen and carbon dioxide.

Seal Characterization
Various techniques can characterize seal performance. Low heat seal and hot tack initiation temperatures, high heat seal strength, high hot tack strength, and excellent seal-through-contamination performance as measured in laboratory tests are traditional methods of evaluating and comparing sealant materials.

While useful in comparing materials, traditional laboratory tests do not always provide a complete assessment of sealant performance. A sealant material or even an entire film structure can look good in heat seal and hot tack testing but perform poorly during an actual packaging trial, shelf-life testing, or distribution. To determine real-life packaging integrity, actual testing of packages made on a pilot or production scale is necessary.

Experimental Procedures
To compare the package integrity provided by POP to other materials, coextruded blown films were manufactured, fabricated into pouches on a vertical form/fill/seal machine, and tested to determine leaker rates. The paper examines four comparisons.

In the comparison of a POP material to a linear low density polyethylene (LLDPE), seal initiation and hot tack initiation temperatures favorably decrease as the amount of plastomer in the sealant layer increases. This improvement is also evident in the effective seal range shown in the seal integrity test results.

The key advantages of using the POP material in the sealant layer at 60%, 80%, or 100% include excellent sealability at low temperatures, decreased heat seal and hot tack initiation temperatures, and increased seal range for optimum package integrity.

Conclusions
Testing package integrity of actual bags is essential for distinguishing the final package performance of different sealant resins and film structures. Laboratory testing provides good basic information about seal performance but needs supplementation with package integrity testing for the complete story. POP materials manufactured using a single-site catalyst provide excellent seal performance when used in a properly designed packaging structure. These polymers provide a wide operating window for packaging machinery and give excellent integrity in actual packages.

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