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PET containers with metal vacuum closures poised to break glass (packaging) ceiling

Crown PET containers with metal closures
The plastic containers are lighter than their glass counterparts and are less likely to break, a benefit for consumers, retailers and affiliated brands alike.

For everyday consumers, it might not be a big deal. At least, not at first glance. But soon, an exciting new technology will enable consumers to purchase more of the products they love, such as pasta sauce, pickles, salsa and jams, in unbreakable clear plastic containers with metal lids.

Innovation efforts at Crown Holdings Inc. (Philadelphia, PA) led to the first commercialization of metal vacuum closures with plastic (PET) containers on mainstream consumer products. Crown announced this development in the summer of 2016, less than one year after initial market testing. The vacuum metal closure/PET container combination is now available on retail shelves for Wegman’s private label pasta sauce, and will soon be available on LiDestri Food & Drink’s Francisco Rinaldi pasta sauce. More products using PET containers and metal vacuum closures are on the way.

For decades, U.S .consumers have been buying hot-filled and pasteurized foods in glass containers with metal closures. Metal closures have seen limited use on plastic containers until now because of technical and aesthetic constraints.

For hot-fill products, the use of metal lug closures typically required the container to undergo a special process treatment to give the thread portion of the jar a very hard (crystalline) structure to ensure the container opening stays round and maintains a good seal. Consequently, the thread area is an opaque white compared with the clear jar body. The container’s appearance was an obstacle to mainstream acceptance by consumers. As a result, the use of metal lug closures on PET bottles had been limited to products, such as honey or nut butters, that didn’t require hot-filling or pasteurization.

The new metal closure/PET container designs are better able to ensure that the thread portion of the container remain round and maintain a robust seal without the aforementioned aesthetic issues. The resulting containers are lighter than their glass counterparts and are less likely to break, a benefit for consumers, retailers and affiliated brands alike.

These advances are the culmination of Crown’s work and collaboration with partners that manufacture PET containers. The development process involved extensive testing at Crown’s facilities, using cappers and other equipment that mimic real-world conditions found on production lines. Maybe best of all, the new closure technology is compatible with Crown’s existing straight-line vacuum cappers, meaning brands will not need to revamp production lines if they choose to switch to PET containers from glass.

Crown’s new closures for large-diameter PET containers are equipped with a modified configuration incorporating five to eight lugs, depending on the size of the container mouth. (“Lug” is the term used to describe the formed tabs on the inside rim of the closures that engage with the threads on the containers; adding additional lugs spreads out the engagement pressure more evenly.) The modified lugs strengthen the seal and improve package integrity, while the PET container reduces weight and breakage when the containers are warehoused, in transit or on shelves.

As lug closures increase in diameter, they historically have an increased number of lugs to help even out engagement loads and pressure points. Leveraging this knowledge became the aha moment during the innovation process, but it was just one piece of a much larger puzzle.

The gasket channel in the closure was optimized to better work with plastic, and a proprietary gasket compound was developed to ensure seal integrity even as the seal surface of the jar moves slightly during high-heat conditions. Working with its partner companies, Crown also optimized the container thread finish design and shared insights on body geometry and container strength to make sure existing straight-line cappers could grip the jars without causing excessive distortion. As a result, the same high-speed capping of containers on glass filling lines can be achieved with the plastic containers.

The benefits are enormous.

When a glass container breaks during the filling process on a high-speed assembly line, clean-up work can cause hours of down time. But a PET container is almost unbreakable.

The PET containers also provide significant logistics advantages. PET containers are up to 30% lighter, so more products can be loaded on a truck when moving through the supply chain.

The widespread commercial launch of this innovation was a major milestone for Crown, which feels that it could significantly alter the packaging space in the coming years.

Galen German is Manager, Metal Closure Development, at Crown Holdings Inc. In more than 18 years with the company, he has focused on improvements and developments in the world of metal closures. He graduated from Ohio State University with a degree in mechanical engineering. For more information about this technology, contact Sheila Heath, Director of Market Crown Metal Closures and Specialty Packaging, by phoning 740/681-6577 or emailing her at sheila.heath@crowncork.com.

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