A Transparent Solution for a Full PE Barrier

A unique partnership involving four major manufacturers supplying the flexographic print industry has resulted in development of a high-barrier mono-material full polyethylene transparent solution, representing an alternative to metallized polyester film.

This innovative filmic substrate, developed with packaging in mind, is free of ethylene-vinyl alcohol (EVOH) and eliminates the need for a topcoat. Enhancements made to earlier versions of mono-material machine direction-oriented polyethylene (MDO PE), via incorporation of the aluminum oxide (AlOx) GEN II process, are credited with being the driving forces behind the development.

Partners involved were BOBST, Dow, Zermatt and Sun Chemical. Together, they looked at global market trends for sustainable flexible packaging, generally grouped into three pillars of sustainability: mono-material polyolefins; compostable, biodegradable and bio-based and paper/fiber-based; then chose to focus on the first pillar—mono-material. A decision was made to use polyolefin- (PP/PE) based solutions, categorized into a single polymer family, to improve recyclability.

Working with a definition of a mono-material contained in Circular Economy for Flexible Packaging (CEFLEX) guidelines (see Figure 1), developers were successful in meeting the stated requirement that the packaging structure needs to be compatible with the current mechanical recycling process and contain at least 90 percent by weight of PE or PP. Other components, such as adhesives, coatings and inks, can have a maximum of 5 percent by weight each.

Specific actions taken by collaborators follow:

• The first stage in its creation was the resin production by Dow. A special resin was designed to maximize thermal resistance and coating and deposition reception to achieve the barrier requirements
• The film was then produced by Zermatt, which used its blown PE line, installed in a facility in Spain to produce 12 rolls of MDO PE film
• Reels were then sent to Italy, where a primer layer was applied on the MDO PE film using a oneBARRIER EXPERT COATER at Bobst Italia’s Competence Centre
• AlOx deposition, using the GEN II process, was then applied on an EXPERT K5 metallizer in Bobst Manchester’s Competence Centre, followed by an adhesive, which was applied on the NOVA SX 550 solventless laminator. Figure 2 serves as a schematic
• Figure 3 shows the results obtained by applying different primers coded A, B, C and E. Primer C and E didn’t give the barrier performance that is required. They won’t be taken forward
• With both primers A and B, combined with AlOx GEN II, a barrier performance of a water vapor transmission rate (WVTR) ≈ 2 g/(m² d) and Oxygen Permeation Testing Analyzers (OTR) < 1 cm³/(m² d) can be achieved

Structure & Solutions

In terms of packaging structures, there are two significant megatrends in the market:

• A big push toward packaging simplification (delayering)
• An ambition to move from non-recyclable mixed polymer solutions to more recyclable mono-material solutions

Figure 4 illustrates this. On the left is a typical structure based on a multi-material duplex laminate. On the right is an example of a mono-material solution, incorporating MDO PE with a special co-extruded EVOH layer, which is added to the skin of the MDO PE, to improve the oxygen barrier performance; as well as to provide an improved metal receptive skin for the AlOx deposition. The objective is to improve overall barrier performance.

Optimized & Economical

By intent, oneBARRIER is a family of full PE high-barrier solutions, which has been designed to maximize the amount of PE in the packaging structure to increase the recyclability and at the same time offer a more economical high barrier.

The concept behind its creation is to provide an optimized metal oxide receptive layer, via wet dispersion coating, where typically thinner layers can be achieved, compared to co-extrusion methods.

Vacuum deposition provides an extremely thin and efficient barrier layer, but performance is dependent on the chemistry of the surface to be coated. Combining these thin and efficient methods of dry vacuum coating and wet dispersion coating together with an optimized base film is responsible for the new packaging film that is the subject of this article. Figure 5 confirms the amount of PE in the structure has been increased to 93 percent.

Bond Strength

Barrier performance increases (Figure 6) for both WVTR and OTR can be seen throughout all the steps in the process. The transparent solution provides a barrier performance equivalent to that of metallized polyester (< 1 cm³/(m² d) and < 1 g/(m² d) and the market requirement in terms of laminate bond strength (2–3 N/(15-mm.) is also satisfied.