Lid Stock Advances
While aiming for improved opening performance for consumers in peel-push and peelable child-resistant blister designs, Alcoa Flexible Packaging’s Safety-Pak Plus lid stock supports more-reliable production on blister equipment.
In the Safety-Pak Plus family of blister backings, the traditional child-resistant blister lid stock lamination of paper, PET, and foil is replaced with a heavier-gauge PET laminated to foil. The peel-push configuration uses a 50-µm PET film/release adhesive/25-µm aluminum foil/ vinyl acrylic heat-seal coating. The structure expands temperature operating windows by 50ºC, compared with standard lid stock formats, says Georgia Mohr, product manager, Alcoa Flexible Packaging (Richmond, VA).
“Heat transfers through the PET more readily than through a paper and PET laminate, because paper is a tremendous heat sink. With the improvement in heat transfer, you can produce reliable seals at higher speeds. Safety-Pak Plus lidding produces very good seals at temperatures as low as 120ºC. You have the flexibility to run at lower temperatures to protect heat-sensitive product,” Mohr says.
The Safety-Pak Plus Peel Push specification features a redesigned release adhesive with improved heat resistance, the company reports. The adhesive prevents delamination under the high heat of platen and rotary sealing, while still affording a clean peel.
“The lid stock functions as it is designed, as a two-step opening process. Seniors become frustrated with standard lidding when peeling is difficult or rips the foil. Our clean, even peel will decrease this frustration,” says Mohr.
Safety-Pak Plus resisted 140 psi before bursting in the Mullen test.
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The heavy-gauge PET is more puncture resistant than traditional blister lid stock, promoting enhanced child resistance. Alcoa tested the packages for puncture resistance with a pierce test and the Mullen burst test. The Mullen test measures a substrate’s ability to resist penetration from a hydraulic ram. Compared with a traditional lid stock, the Safety-Pak Plus lidding required application of more than twice the pounds per square inch before failing.
“These two tests mirror each other very well, for simulating a child biting into a package,” Mohr says.
The child resistance afforded by PET carries over to the Safety-Pak Plus PL (peelable) lid stock that features a peelable heat seal coating for sealing against thermoformed or foil blisters. Maximum CR is provided by the Safety-Pak Plus LT (Lock Tight), which requires a tool to open.
For supporting OTC merchandising, an acrylic print primer on the PET substrate supports higher-quality printing than has been possible with paper laminates.