New tamper-evident seals offer clear and clean-looking packaging that is easy to open and reclose.
 Matching method with material

Depending on the product, equipment suppliers offer a range of tamper-evident closures. For bars, snack cakes and bread, producers can opt for cold, hot or ultrasonic sealing.

Cold seals are not as tamper evident as hot and ultrasonic seals. For a cold seal, food manufacturers use an adhesive substance to secure the edges of packaging. Applying pressure to the packaging material produces the seal without a heat source.

Bill Kehrli, vice-president, sales and marketing, Cavanna Packaging, said this type of seal provides a basic, minimalistic form of tamper evidence. This popular, easy-to-use seal allows food companies to ramp up the speed on a production line. Mr. Kehrli said the Cavanna Slim continuous motion horizontal wrapper can run 800 chocolate coated bars per minute with a cold seal.

“It can run very fast, and chocolates don’t like heat, so companies avoid heat seal for these,” he said.

Heat sealing melts materials together, and some machines crank out up to 400 bags per minute, depending on the thickness of the film. These seals offer cost-saving benefits, said Mitch Lindsey, technical sales, Burford Corp. They can work alone as a tamper-evidence feature without needing an adhesive or twist tie. Or, a food manufacturer can put a heat sealer in line with a twist tyer or another closure machine for consumer convenience and reclosability.

Burford’s TEC200 system creates an easy-to-open perforated bag tail and works with existing servo tyers. It features a non-contact heat-sealing method with patent-­pending hot air flow that can seal up to 100 bags per minute.

A relatively new technology, ultrasonic sealing uses high-speed impulses that collide into each other, creating friction between layers of a bag’s film that generates heat and a seal. The process typically operates slower than heat- and cold-seal methods at fewer than 100 bags per minute.

The ultrasonic method is extremely tamper-evident, Mr. Kehrli noted. Someone would need to basically destroy the package to open it. This process, however, is used more prolifically in pharmaceuticals than in the baking industry. In Europe, some snack cake companies employ this method to extend shelf life and eliminate the spray of preservatives onto products.

“They can do that by using a nitrogen gas and ultrasonic sealing, and they believe they’re going to get similar and improved shelf lives,” Mr. Kehrli said.

Each method provides advantages and disadvantages. Bakers must decide the right mixture of line efficiency, material cost and level of security on the closure for their operation and product.