by Jennifer Dean
Thirty-seven years ago a knowledgeable group of people created the standard for flexible package seal strength testing. The F88, created by the F02 committee on flexible barrier materials of the American Society for Testing and Materials (ASTM), created the standard to determine the seal strength of flexible barrier materials.
Today, millions of seal-strength measurements are used to qualify materials for physical package testing. Over time, ASTM F88 has undergone many revisions. But the original three-page document has remained the foundation of today’s standards.
In 2000, members of subcommittees F02.3 on food and consumer packaging and F02.6 on medical device packaging worked together to address conflicting data issues found when laboratories use different techniques in their testing. Members of the Sterilization Packaging Manufacturers Council (SPMC) Technical Group volunteered to design a new protocol, produce laboratory samples, coordinate the labs and analyze data for a new statement that would encompass the many modifications made to the original document over the years.
Members of this group came from many businesses, including Amcor Flexibles, Beacon Converters, Oliver Products, Perfecseal, Rollprint Packaging Products and Tolas Health Care Packaging. There were also participating volunteers from Cryovac, DBI, Inc., Distribution Dynamics Labs, Inc., Eastman Kodak Co., Edwards Life Sciences, Kraft Foods, Inc., Michigan State School of Packaging and Vinatoru Enterprises.
An Interlaboratory Study (ILS) approach was used to define repeatability – the amount of variation when samples are tested in the same lab, with the same operator, using the same equipment in a same day setting. ILS studies the amount of variation found between those labs.
The SPMC group studied more than 2,000 seals in a testing protocol that was designed to comprise three independent round-robin test series. All testing was based on use of peelable seals.
Test series A evaluated a coated paper and film combination for differences in speed of crosshead travel and for two different techniques of tail peel angles. Series B took an uncoated material with the 1073B Tyvek/film combination and kept the crosshead speed consistent while again varying the control of the tail angle of peel.
An addition test was performed using reverse direction in order to demonstrate what occurs when less flexible material is bent back, while more flexible material is supported by the backing plate.
Test C took a sealant material common to the two substrates of different caliper and sealed them face-to-face to measure the effect of a change in flexibility to the measured value.
Results of the testing demonstrated a significant difference in results depending on how the tail is oriented – the grand average of seal strength changed with each technique of handling the tail of the seal – and a change in flexibility was noted when tested supported or unsupported.
This knowledge was noted and is now part of the F88 standard.
The round robin approach taken by SPMC produced the necessary common knowledge that allows today’s testers to feel confident that their data reports will now agree with data from other labs, creating a more stable, dependable results standard.