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Fruit jars stand up, stand out

Signature Fruit works with blow molder to develop a wide-mouth plastic jar that withstands pasteurization for packing premium California fruit.

Seven-layer jars made with clarified polypropylene let the fruit show. New label graphics for the Libby's brand helped capture r
Seven-layer jars made with clarified polypropylene let the fruit show. New label graphics for the Libby's brand helped capture r

A custom multilayer blow-molded jar is now giving customers of Signature Fruit Co., Modesto, CA, a new look at peaches, apricots, and fruit medley. That’s because the 63-mm wide-mouth jar is molded of a clarified polypropylene to yield as clear a package as possible.

The jars were developed by Signature and Graham Packaging over many months of testing. The key requirement that needed to be met was that the plastic jar had to be able to withstand post-fill pasteurization, says Don Jepson, director of engineering at Signature (formerly known as Tri-Valley Growers).

“Our process is what we call ‘warm-fill’ and then ‘post-sterilization,’” Jepson says. “So the jars needed to be able to withstand the cook process and that resulted in going to polypropylene. It’s a polypropylene coextruded with an oxygen barrier and also a barrier to ultraviolet light.”

Graham uses a resin master batch that’s blended with a clarifier to make the jar as transparent as possible, according to Jay Arnold, spokesman for Graham Packaging. “A lot of the newer polypropylenes have new clarifiers added.” The jars weigh 54 g and comprise seven layers, including a layer of ethylene vinyl alcohol copolymer for its oxygen-barrier properties, Arnold points out. “We had to add some gram weight to the jar so that it could withstand the pasteurization,” he says.

“Clarity was an issue that we worked on with Graham. We wanted it to look as clear as a PET bottle, but they can only work with resins that can withstand the processing,” Jepson adds.

In addition, the jar is sealed with a PP screw cap with a steel insert, much like old canning jars, he adds. The cap is from Crown Cork and Seal and it’s called the Ideal 63-mm finish with four-lead lug. It also incorporates a tamper-evident breakaway band. “We did about six months of pilot lab work to find a system that would provide adequate seal integrity and process performance,” Jepson says.

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