Design for sustainability Ready for the future: Solutions for tethered bottle caps

Source: GF Machining Solutions

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By 2024 drink bottles made of plastic must be produced in such a way that the cap is firmly attached to the container. This requires new design concepts that are also reflected by the machines used to manufacture the moulds.

New tethered cap design with a plastic tether to secure the loose cap
New tethered cap design with a plastic tether to secure the loose cap
(Source: GF Machining Solutions)

Plastic is an integral part of modern day-to-day life. At the same time, there is an increased focus on responsible consumption of plastic and combating pollution, especially due to single-use plastic products. Over the last few years, multiple studies have highlighted long-term pollution due to single-use plastic products. That is why in May 2018, the European Union announced a new directive, EU 2019/904, on how to deal with single-use plastic products and fight pollution related to littering. One of the main clauses in this extensive directive targets pollution due to loose caps and mandates, beginning in 2024 that drinks can only be sold in plastic containers if the cap remains attached to the container. According to the directive, every single-use plastic bottles holding less than three liters must be filled in a packaging container equipped with a tethered cap.

The mandated tethered caps must remain attached to bottle throughout the whole consumer journey. The market has seen an influx of such solutions with diverse design concepts. Tethered caps are the subject of much discussion in the beverage industry. Since the announcement of the EU directive, specialists have been working hard to find beverage cap solutions to meet its requirements.

Development of these new tethered-cap bottles for packaging requires two critical updates to the current process: First, new design features must ensure tether functionality. Secondly, mould manufacturing, injection moulding and plastic processing have to be optimised. To achieve the tether functionality, producers focus on three-design features:

  • 26/22 neck finish
  • Locking mechanism for prolonged use
  • Unbreakable cap lid, resulting in significant changes in the design of the neck ring, caps, thread, and the mould and injection moulding processes

Furthermore, the mould makers recognize the need to adapt their processes to meet the market’s future needs for productivity and quality. Mould manufacturing for the tethered caps requires:

  • Extended reliability of individual machining process such as milling, electrical discharge machining (EDM) and grinding
  • Integration of machining technologies in single automated process to ensure productivity and repeatability
  • Ability to machine close tolerances for plastic injection of sharp features, thin walls
  • Elimination of any time- or cost-intensive processes from the manufacturing chain
  • Shortening of the manufacturing, injection and sourcing supply chain

What is Directive (EU) 2019/904?

This EU directive states that “beverage containers that are single-use plastic products should only be allowed to be placed on the market if they fulfil specific product design requirements that significantly reduce the dispersal into the environment of beverage container caps and lids made of plastic.”

According to Article 6 of the directive, “Member States shall ensure that single-use plastic products listed in Part C of the Annex that have caps and lids made of plastic may be placed on the market only if the caps and lids remain attached to the containers during the products’ intended use stage.” This refers to beverage containers with a capacity of up to three litres, i.e. receptacles used to contain liquid, such as beverage bottles including their caps and lids and composite beverage packaging including their caps and lids.

GF Machining Solutions' complete machine tool solutions for mastering polyethylene terephthalate (PET) bottle manufacturing.
GF Machining Solutions' complete machine tool solutions for mastering polyethylene terephthalate (PET) bottle manufacturing.
(Source: GF Machining Solutions)

Various machines to choose from

To design and manufacture innovative moulds, manufacturers around the world rely on highly precise machine tools such as those offered by GF Machining Solutions. The portfolio of the Swiss company includes milling, EDM, laser texturing, laser micromachining and Additive Manufacturing machines. Additionally, the division of the Georg Fischer Group offers spindles, automation, tooling and digitalised solutions backed by customer services and support. These solutions enable them to achieve the desired results with precision, accuracy and flexibility.

1. Preform moulds: A typical preform mould consists of a deep cavity, a preform cylindrical core and a neck ring. GF Machining Solutions offers the comprehensive technology to manufacture preform moulds. The Mikron Mill S 400 U high-speed Milling machine with built-in jig grinding capability allows manufacturers to achieve uniform circularity and surface polish on the preform core and cavity. The DMP Flex 350 solution makes it possible for manufacturers to capitalise on Additive Manufacturing (AM) technology’s ability to machine internal cooling channels in tougher materials in order to produce heat-critical neck rings, thereby significantly enhancing mould productivity.

2. Caps and closure moulds: The company’s EDM technology offers a solution for producing moulds for caps and closures. With the Agie-Charmilles Form P 350, manufacturers can structure cap mould cavities, achieve ideal replication in injection moulding, easily machining grooves, teeth and branding features. Additionally, the Agie-Charmilles Laser S offers unique opportunities to digitalise mould manufacturing for high-quality caps with innovative designs and features. The Agie-Charmilles Cut X 550 delivers the high accuracy, parallelism, and aligned taper on tall components, perfectly producing precision mechanisms such as collapsible cores required for seamless ejection of threaded elements.

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3. Blow moulds: GF Machining Solutions offers a 5-axis blow-mould manufacturing solution combining the Mikron Mill S 600 U for high-speed milling and the Agie-Charmilles Laser S 1000 U for Laser texturing. The solution offers mould makers the complete flexibility to innovate and produce while controlling their mould manufacturing processes to meet the PET bottle manufacturing industry’s current and future needs, including thin walls, functional designs, productivity and new materials.

These solutions, combined with GF Machining Solutions’ automated workflow, represent a unique PET bottle mould manufacturing process to provide a distinctive competitive advantage with significant productivity, quality and cost gains for manufacturers. Manufacturers profit from the improved process reliability they need to produce new PET bottles with tethered caps. The shape complexity of such tethered cap bottles warrants an integrated manufacturing chain and closer mould manufacturing supply chains to achieve best-in-class packaging. Mould manufacturers need to master multiple machining technologies. Automation and reliability also play an important role in ensuring their future profitability. GF Machining Solutions provides mould makers with the innovative machining solutions they need to increase the sustainability of the plastics processing industry.