Designers close in on meeting rules for tethered caps

A large segment of the beverage industry went to tethered caps decades ago following public outcry about shrapnel-like aluminum pull tabs from beer and soda cans posing health and ecological risks.

All those sharp-ended metal ring pulls glimmering at beaches and parks shined a light on the growing problem.

So did singer Jimmy Buffett, who bemoaned cutting his heel when he stepped on a pop top and blew out his flip flop in his 1977 hit song "Margaritaville."

The beverage industry responded to the problems, according to Jay Yuan, the principal of Houston-based Stress Engineering Services Inc. He has worked in the U.S. packaging industry for 24 years.

"The invention of stay-on tabs caught fire in the 1970s. That's the technology that eliminated one of the nation's most common pieces of litter. What is the equivalent for plastic caps?" Yuan asked.

He posed a question that design engineers must answer relatively soon during Plastics News' Plastics Caps & Closures 2020 virtual event.

By 2024, the European Union is requiring all single-use plastic beverage containers with volumes of 3 liters or less to have closures that remain affixed to the bottles.

So, now it's the plastics industry's turn to do something about all its colorful caps littering beaches and swirling in ocean gyres.

Michael White, business development manager of beverage closures at Bolton, Ontario-based Husky Injection Molding Systems Ltd., said the legislation passed by the EU in 2019 is resonating in North America.

"We believe it's basically the first domino to fall," White said. "The states of California and Maine are looking at introducing similar legislation. And Canada is looking at criteria there. The thinking is that by tethering small closures to the bottle itself, it's more likely to be recycled than simply discarded."

Husky representatives have been active with an EU steering committee formed to help establish the standards there. White said the minimum performance guidelines call for closures to withstand a minimum of 15 openings and closings without the tether being compromised as well as a separation, or pull force, of 25 newtons in the vertical or horizontal direction.

"This is a value that all closure developers in the industry are targeting currently," White said, adding the value could change before the law is enacted in 2024.

The pending requirements raise a slew of design considerations as to the bottle neck type of tether to use – lanyard loop, helical tether, hinged or other – as well as branding, shelf differentiation, sustainability and the consumer experience.

"We see this as an opportunity for brand owners and converters alike," White said. "It's a way to talk about sustainability on the shelf. You can promote the fact the closure is tethered to the bottle. The brand is making an effort to promote sustainability."

And, any time you have an opportunity to tell a story about something new related to your product, "It's a good thing," White added.

A plastic bottle cap consists of a shell, the tamper-evident band, and the bridge that connects them. The bridge indicates if there has been any kind of product tampering by fracturing or turning white.

A tether adds another layer of complexity for designers, who need to meet legal requirements while balancing consumer expectations without sacrificing performance, particularly in terms of carbonation level depending on the beverage.

"You want to make sure features like opening torque, bridge break torque and other design considerations are met," White said.

For example, nobody wants to sip their water or chug a sports drink with the shell of a tethered cap flapping against their face.

"You want to eliminate anything that could potentially detract from the current experience," White said.

Designers also need to be wary of introducing a tethered closure design that gives them a weight penalty. White said Husky is targeting weight neutrality.

"Some enhancements have a slight weight penalty, but it depends on how you want to position your brand," he added.

Jason Phillips agrees. He's the group creative director of Force-4 Innovation and Collaboration Group, which is an affiliate under Stress Engineering Services based in Mason, Ohio.

Phillips said he sees the tethered cap as a way to catalyze an overall new presentation for the brand and package.

"Think of the tethered cap as a jewel so to speak in terms of its focal interest for the brand and an interactivity point for the consumer," he explained.

Caps can be affixed by hinge, canteen-style lanyard loop, or a helical tether that consists of a bottom band with a retaining ring and a middle band that produces a long tether as the cap is unscrewed.

Husky has a patent pending on a hinged design that retains the shell in position. When you open the closure, you feel and hear a click as the integrated hinge locks the shell in place.

"It's a more premium approach that allows the true 180-degree shell locking," White said. "…You have that tactile feedback, and you know its locked into place."

Looking ahead, Yuan expects designers to find new ways to make tethers aesthetically pleasing and fun.

"The cap could be something of a flourish or more playful," he said, describing a spiral decoration as an example.

The transition to tethered caps is part of EU-wide rules that target the 10 single-use plastics products most found at Europe's beaches as well as lost and abandoned fishing gear. The 10 items represent 86 percent of all single-use plastic items on beaches, and about half of all plastic marine litter.

In addition to bottles and caps, those items are food containers, beverage cups, cutlery, cotton bud sticks, balloons, balloon sticks, packets and wrappers, and plastic bags.

For businesses weighing consumer preference against economic factors, sustainability initiatives can pose complex problems, but there's no discounting it's important going forward, Phillips said.

"We believe defining future experiences will be a combination of delivering on sustainability as well as the core experience of whatever that package or product might be," Phillips said. "In some cases, the experience of sustainability … is as important as the core feature or function of the product itself."

During the design process, virtual simulation technology can provide information about everything from molding process constraints to sealing performance, according to Mandar Kulkarni an associate at Stress Engineering Services, who has been in the packaging industry for six years.

"Tethered caps pose engineering challenges for an otherwise mature closure technology industry," he said. "Virtual simulation technology can eliminate the bulk of design prototype test iterations and improve speed to the market for the new product development cycle."

The technology provides engineering details and insights that answer a myriad of questions. Does the cap's removal torque fall within specifications that are easy for the consumer? Does the design modification of the tether affect the sealing in any way? Is the manufacturing process friendly? Does it fall within molding constraints? How can the design be more suitable for existing manufacturing technology?

"To answer all these questions, we can use virtual simulation technology, or the digital twin of the real world, to evaluate the performance and eliminate the bulk of the design prototype test iterations," Kulkarni said.

Husky, which is in the segment from a tooling standpoint, has patents pending on several designs. The company did capping trials in the lab and with customers on its 180-degree shell design, running 10,000 samples of the hinged tether on pilot and production lines with no issues.

The team is on track to validate its design this month. It has a complex geometry with a molded-in bridge that requires no secondary operations and the integrated hinge for consumer ease.

"A premium tether that you can lock in place is a great opportunity to say, 'Look at my brand; I'm making a sustainable effort,'" White said, "and it provides a seamless and intuitive and positive user experience."