Tethered trends: Exploring the impact on cap moulding lines

The EU recently introduced a directive on marine plastic litter, and tethered caps and closures play an important role. As of May 2024, EU producers, retailers and manufacturers, as well as importers to EU countries will be obliged to implement tethered closures on all beverage containers up to three litres.

 Although Sumitomo (SHI) Demag is not a manufacturer of caps and closures, many of the company’s customers are and have started to question the production challenges they may encounter. UK Managing Director Nigel Flowers explores the challenges and important considerations that moulders can pre-plan for.

In theory, you can produce tethered caps through an existing packaging injection moulding machine just as you would any other closure or container. Cycle times are of course extremely critical, and most closure manufacturers specialising in this sector produce tens of millions of caps per year. In order to succeed, closure moulders will need to examine every potential tethered ring and cap application – press on, side clip, flip top, carbonated screw cap – to ensure that the selection of materials, machine and tooling give the optimum blend of speed, quality and processing repeatability.

Impact report

Several years ago, PwC conducted an impact report study estimating that the changeover cost could reach up to €8.7 billion[i]. This will of course be very dependent on how extensively neck finishes on beverage containers need to be changed. These forecast costs cover capital investment costs as well as significant losses of productivity and downtime for existing operations while lines are being reconfigured.

Looking specifically at the moulding processing conditions, these in theory won’t change considerably. Providing the material isn’t altered, melt stability will be the same. The main investment outlay will be in mould tool design, which may require increasing the mould space of injection moulding machinery or opting for a larger tonnage packaging machine. A number of mould toolmakers have already committed to increase, some double, their production capacity in this space to cater to increased demand for replacement mould tools.

Mould tool cavitation

High cavitation mould tools – 64, 72, and 96 – are commonplace in closure production, due to the high volumes required. Adding the tether ring into the mould design either means reducing the number of cavities in the tooling, or increasing the size of the mould tool and consequently the mould space and tonnage of injection moulding machine to accommodate bigger tooling.  Additionally, if the shot weight and part weight of the closure component increases, a greater injection unit capacity may be required.

The machine selected will be dictated by mould design and the cavitation layout. Higher pressures and speeds, faster cooling times, and modifications to part-ejection and gating arrangements are all important factors to keep in mind.

Machine advances

To support these efforts, Sumitomo (SHI) Demag continues to pioneer the development of packaging machines. The company’s El-Exis  SP  range,  available  globally,  now  comprises  10  machines,  with  a  clamp  force  range  of between 150 and 1,000 tons.

Capable of delivering dry cycle times of less than two seconds, this latest generation of EL-Exis SP’s is specifically designed to withstand the higher stresses and injection pressures that are so critical in achieving repeatability. The range is aimed squarely at high volume manufacturers of polymer products, particularly caps and closures, and the new 1000 ton machine can easily accommodate a 96 cavity tether cap and ring tool. With the introduction of a new control valve regulating the hydraulic pressure during the loading of the accumulator, the range consumes up to 15% less energy that previous generations of El-Exis machines.

Reducing the cavitation of a tool to 64 or less might warrant closure moulders considering the efficiency and energy saving merits of an all-electric machine. Several closure moulders developing tamper evident closure bands have invested in dedicated IntElect all electric machine cells in recent years as they deliver consistent moulding precision. Additionally, the newest IntElect’s feature an increased tie bar distance which significantly increases the mould space. This means they can accommodate larger mould tools combined with very small injection units. The ability to install small screws matched with a large mould space is a big advantage as it improves the dosing and injection performance.

Quality control

Processing consistently is equally important to the integrity of the tether ring which slides over the neck thread of a beverage container. Extra tests may need to be performed to ensure shrinkage doesn’t occur, or conversely the tethered cap ring stays attached to the bottle. An integrated vision control system is more than capable of monitoring these processing conditions.

An automated example was showcased at last years’ K Show.  Featuring the inspection Capwatcher Q Line from Intravis, eight high-resolution cameras collect, visualise and provide up to 144,000 cavity-based measurements per minute. It also sources a unique inline temperature measurement for each closure, which allows moulders to determine the shrinkage behaviour of each and every closure. From a quality control perspective, this is groundbreaking stuff and significantly reduces production waste.

[i] https://www.newfoodmagazine.com/news/76731/pwc-plastic-carbon-cost/


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