Flexible packaging is currently experiencing a period of enforced transformation.
The world’s biggest brand owners are committing to various sustainability pledges, examining how they package their products and evaluating functionality requirements seen as critical to their needs. As a result, megatrends have been born. Alternative solutions, developed through collaboration right across the value chain—including brand owners, resin producers and asset manufacturers—are now available. Partnerships have created barrier solutions that are fully compatible with the latest sustainability requirements and the circular economy.
All images courtesy of Bobst
A fundamental principle driving sustainability agendas is the shift from a linear economy to one that is circular. That has huge implications for the flexible packaging industry. Traditionally, a film would start life from a fossil fuel or crude oil, be made into a polymer and then converted to add value, or functionality, through a variety of processes—metallization, wet coating, lamination and printing. After use, this packaging would then go into a waste management stream for incineration, or be sent to a landfill.
This linear economy has been the primary route to manage our packaging detritus for many years. Although successful recycling streams are now prevalent in certain parts of the world, these tend to be dominated by rigid, non-flexible products.
Alternative recycling routes for flexible packaging are now being developed:
- Mechanical recycling involves the cleaning, separation and re-granulation of the structure into a PCR (post-consumer recycled polymer) and gives the material a second life as a packaging film, or as a downcycled polymer in a different rigid plastic application. Polyester (PET) films can be recycled in this way and market-ready solutions exist today with up to 90 percent PCR content. This is not cheap, nor seemingly the way the market wants to go
- Chemical recycling is a much newer concept and is a huge area of focus for the largest companies who are striving to return mixed plastic waste back to the original polymer. Chemical, or feedstock, recycling involves a variety of technologies, namely: pyrolysis, catalytic cracking and hydrogenation to produce virgin-like polymers and create new plastic items
Figure 1: Layer eliminated! A typical aluminum foil laminate structure consists of a printed web, a barrier layer and a sealant layer. To de-layer, by removing the higher cost and less environmentally friendly foil, as well as the non-polyolefin polyester layer, and move from a Triplex (3 layer) to a Duplex (2 layer) structure, means the barrier and heat sealable layers are from the same mono-material (polyolefin). The thin 7-8nm layer of AlOx, together with protective and barrier topcoat, provide a commercial-ready solution for foil replacement.
Mono-Materials
Barrier solutions providers, like BOBST, have seen a huge increase in demand for high-barrier mono-material solutions, based on polymers that can easily be recycled. These include polyolefins, as well as bioplastic solutions and, more recently, paper-based solutions for high-barrier packaging applications.
Historically, there have been two routes for obtaining high barrier:
- Aluminum foil to obtain the highest possible strength—(OTR ≤ 0.1 cc/m2/day (23 degrees C/50 percent RH) and WVTR ≤ 0.1 gm/m2/day (37.8 degrees C/90 percent RH)
- Co-extruded multi-layer film with the addition of EVOH, or nylon, to further improve the oxygen barrier
Recent changes in terms of laminate structure and substrate material choice have seen a significant move away from this. Two significant megatrends have developed in the market as a result:
- A push toward packaging simplification—layer reduction, or de-layering of laminate structures
- Downgauging for flexible packaging
These environmentally friendly megatrends primarily involve inorganic transparent barrier, using either the AlOx (Alumina), or SiOx processes, to apply a thinly-coated ceramic layer (7-nm. to 8-nm. in thickness) onto polyolefins; in particular MDO PE. This offers the converter a high-barrier, transparent packaging solution that simultaneously offers a bona fide alternative to present structures that is both sustainable and inexpensive to produce, and more importantly, accepted by brand owners and environmental organizations, as compliant with the latest recyclability guidelines.
The primary megatrend is to create a foil-free, high-barrier laminate and then to de-layer. A typical aluminum foil laminate structure consists of a printed web, a barrier layer and a sealant layer, as shown in Figure 1. The focus is to de-layer, removing the higher cost and less environmentally friendly foil, as well as the non-polyolefin polyester layer and move from a triplex (three-layer) to a duplex (two-layer) structure. The barrier and heat-sealable layers are from the same mono-material (polyolefin) and the thin 7-nm. to 8-nm. layer of AlOx, together with protective and barrier topcoat, provide a commercial-ready solution for foil replacement with a barrier of around OTR ≤ 0.1 cc/m2/day (23 degrees C/50 percent RH) and WVTR ≤ 0.1 gm/m2/day (37.8 degrees C/ 90 percent RH). These results are groundbreaking in terms of barrier levels using polyolefins only. Essentially, they are the culmination of extensive research and development conducted at the Bobst Manchester Competence Centre over the past one to two years.
“A fundamental principle driving sustainability agendas is the shift from a linear economy to one that is circular. That has huge implications for the flexible packaging industry.”
This work is also closely linked to the second megatrend, which is MPET (metallized polyester) substitution and creating structures with a “mono,” or single polymer material, as shown in Figure 2. The aluminum opaque layer is replaced with a transparent inorganic AlOx or SiOx barrier layer and combined to the printed web. The print can still be viewed through the transparent barrier layer. As AlOx and SiOx are both transparent in the visible and UV wavelengths spectrum, packaged products are generally limited to those not needing UV barrier. Impressive results offer barrier values for both oxygen and water (OTR ≤ 1.0 cc/m2/day 23 degrees C/50 percent RH and WVTR ≤ 1.0 gm/m2/day 37.8 degrees C/90 percent RH) that make inorganic transparent barriers a commercially viable and sustainable alternative to existing multi-layer or foil-based structures. And, they are fully recyclable.
In terms of flexible packaging market demands for mono-material, with ideally PET- or aluminum foil-like barrier values, newer substrates are being developed and optimized to meet sustainability requirements. These are generally olefin (PE/PP) and paper-based for recyclable solutions, and biopolymers, such as PLA (polylactic acid), PHA (Polyhydroxyalkanoates) and cellophane for compostable, biodegradable or marine degradable.
Film Production Tech
Materials that previously have proved challenging to dry coat, due to their mechanical and thermal properties, now offer a solution, due to advances in resins and film production technology—in particular polyethylene (MDO). PE has some attraction from a recycling perspective, based on its low density and low melting point.
Extensibility challenges can be overcome with new orientation techniques, via pos-blown inline MDO at converter sites, to improve mechanical stiffness and optical transparency. The development of PE resin technology continues at pace and the increased use of MDO technology to improve mechanical properties of the film, as well as incorporating certain HDPE elements, offer new possibilities for further barrier improvement. These advances, together with the latest developments in dry coating technology, mean new possibilities for PE incorporating high barrier.
Transparent inorganic barrier offers realistic possibilities for recyclable packaging. The AlOx and SiOx processes give the converter a versatile method of production to not only protect the product and extend shelf life, but also offer a robust solution for subsequent conversion steps. Bobst, as a supplier with extensive experience creating coating, printing and lamination solutions, has validated this process from start to the finish. These latest innovations have been created with the new-generation AlOx process, which is now successfully in the market and has been specifically optimized for polyolefins to further improve transparency and barrier.
New developments herald a breakthrough in the rapid evolution of sustainable high-barrier solutions. For the first time, many can be developed and produced in-house by the converter. The level of investment required to enter into this flourishing high-barrier segment is no longer prohibitive.
Previously, more traditional processes involving expensive and complex film production on huge machines, combined with complicated deposition techniques, were the only available options. They came at a premium to those with the volume and the budget to do so. The latest solutions in barrier-coating polyolefins have re-opened the door for the converter to a new, exciting world of opportunity and equipped printers to meet the challenges our industry will face over the next decade and beyond.
Hughill presented this information as part of Virtual FORUM 2020 in the session titled Innovation and Technology Born from Frustration. FTA members can watch every presentation from this session, as well as presentations from the other five Virtual FORUM 2020 technical sessions, on MemberConnect.
About the Author
