Tethered caps are caps which remain firmly attached to the bottle after opening and during the product's service life or life cycle

Requirements for the production of tethered caps

FOLLOWING the recent new EU regulation for caps and closures, manufacturers in the EU must ensure that any caps and closures they manufacture must be ‘tethered’ by July 2024 at the latest. Tethered caps are caps which remain firmly attached to the bottle after opening and during the product’s service life or life cycle.

“Plastic closures and lids used for beverage containers are among the single-use plastic items most frequently found as litter on the beaches of the European Union. Therefore, the placing on the market of single-use plastic beverage containers should only be allowed if they comply with certain product design requirements to significantly reduce inputs of plastic container closures and lids into the environment,” reads the relevant part of the EU regulation.

The regulation applies to the caps of all plastic and composite beverage containers up to 3 litres, but not glass or metal beverage containers with plastic closures or lids, or beverage containers intended for liquid foodstuffs for special medical purposes.

The requirements for the design and function of tethered caps resulting from this regulation are currently still being defined and can be summarised as follows at the moment:

  • The closure must be compatible with existing preform designs, openings and thread types
  • Impact on the end customer should be kept as low as possible, i.e. comfort of use should not be reduced
  • Closures are compatible with existing filling equipment
  • Closures are connected to the container throughout the entire product life cycle until recycling
  • Materials for the closures are not changed
  • Impact on existing production lines should be minimised and output not reduced
  • 15 times opening and closing of the cap without loss of function must be guaranteed
  • The connection between cap and container must withstand at least 25 N tensile force


Strategies for the production and design of tethered caps

Jörg Leonhartsberger, Engel’s sales director for packaging, says that currently, two main production concepts exist to achieve the new requirements for the production of tethered caps:

  1. With the ‘slit concept’, the cap is cut after injection – this has the advantage that current tools can continue to be used, but require an additional work step in production and significantly restricts the design scope of the cap.
  2. With the ‘bridge concept’, a band is injected along with the cap, which requires new tools. The advantage of this concept, however, is that no additional work step is required afterwards, greater freedom of design is possible for the caps and the injection-moulded connection between the cap and the band can withstand higher loads.


There are also two dominating variants in the design of tethered caps:

  • The ‘lasso design’ refers to caps that are connected to the bottle with a two-part band. The cap is connected to the upper band and the bottle to the lower band. This design is relatively easy to implement with existing tools, usually only the sliders need to be reworked.
  • The ‘hinge design’, on the other hand, allows the permanent connection of cap and container by means of a hinge, which optionally also allows the cap to be fixed in a defined position. The use of existing tools is practically impossible.


“Due to the high demand in the market, many manufacturers are expected to start with the ‘lasso’ solution first as the hinge design requires high investments in both time as well as financial terms due to the need for a new mould. In addition, the hinge design may require adjustments to the filling line and the feeding of the caps, resulting in further costs,” says Leonhartsberger.

As a trend for the future, it is expected that in the course of the changeover to tethered caps, many producers will consider switching from 1810/1811 cap types to 26mm caps. The advantage here is a possible reduction in cycle time and material usage. For the injection moulding machine, tethered caps require higher injection speeds and increased injection pressure, as the required cavity internal pressure will tend to be higher. The reason for this is the changed filling behaviour with an increased number of filling points on the TE belt. The necessary clamping force, on the other hand, will not increase with a change to a 26mm closure.

“Engel’s new precision injection moulding, the Engel e-cap, is an electric precision machine that reduces production costs significantly using the fastest cycle times, optimum dynamics and exceptional efficiency. Product quality is boosted through totally clean production, and uptime is maximised through total reliability and outstanding service,” says Leonhartsberger.

“No matter whether you produce caps and closures for soft drinks, ketchup bottles or tetrapaks, the highest output rates and maximum machine availability are absolutely essential to guarantee profitable production. Our two fastest high-performance injection moulding machines – e-cap and e-speed – are both: highly dynamic sprinters, absolutely robust endurance runners and much more,” he adds.

Engel’s highly dynamic electric drives combined with intelligent design make its e-cap and e-speed the fastest Engel injection moulding machines ever. Cycle times are down to less than 2 seconds to enable the production of highly profitable caps and closures and similar products.

Components are specially developed for plasticising HDPE with the lowest melt flow index; ensuring trouble-free processing of the material used the most in the caps and closures sector.

  • Engel is represented in SA by Greentech Plastic Machinery