oneBARRIER FibreCycle: A High Barrier Fibre-Based Solution from BOBST & Partners
Monday 18. July 2022 - When looking at global market trends for sustainable flexible packaging, the trends can be grouped into three pillars of sustainability: mono-material polyolefins, compostable, biodegradable & bio-based and paperfibre-based.
BOBST, working with its partners including UPM and Michelman have developed a high barrier, recycle-ready, fibre-based solution named oneBARRIER FibreCycle.
When looking at global market trends for sustainable flexible packaging, the trends can be grouped into three pillars of sustainability: mono-material polyolefins, compostable, biodegradable & bio-based and paper/fibre-based. Within this article, the focus will be solely on the second pillar of paper/fibre-based and how oneBARRIER FibreCycle has been developed.
BOBST along with its partners has created the oneBARRIER Family of solutions which targets all three pillars of sustainability. Last year, oneBARRIER PrimeCycle was launched which is an EVOH-free, top-coat free solution for full PE barrier and is an alternative to metallized polyester film. Following a shift in demand in the industry for more paper-based packaging options, we launched in June this year, oneBARRER FibreCycle, a paper-based packaging solution. We are also actively working on the third pillar and exploring options such as the development of a home compostable packaging option.
oneBARRIER FibreCycle Creation: Primer
To create high barrier paper-based material, a thin layer of primer is required to make the paper surface ready for metallization. In order to coat the paper, we first had to look at how to overcome the challenges of paper which include: it is hydroscopic and strongly absorbs moisture, it has a high surface roughness and a poor barrier. After we understood the paper substrate, we had to select the right chemistry in order to provide the correct barrier and good adhesion, identify the correct coating method and drying profile needed to enhance the paper coating and ensure careful web handling due to the brittle nature of the paper substrate.
The oneBARRIER FibreCycle structure can be seen in Figure 1. The creation of the structure involves two phases of coating: primer coating before metallization and a heat-sealable top-coat afterwards. Both coating phases were carried out in Bobst Italia on the pilot coating machine, whilst metallization was carried out in Bobst Manchester on an EXPERT K5.
Over the past three years, BOBST has carried out intensive paper coating tests, conducting over 300 trials using various paper thicknesses (from 32gsm to 100gsm) and testing various chemistries (PVOH, PU, Acrylic etc) and optimized coating weight for both the primer and top coating. This has given us a lot of experience and know-how related to paper coating.
During the development process, SEM images were used to study the morphology of the paper before and after primer coating (see Figure 2) as the goal it to eliminate the porosity of the paper. On the left, is the paper surface before coating, the red circles highlight the porosity and fibrils. The middle image shows the surface after coating Method B was used which is a single, thin polymer coating pass. There are still a few visible fibrils on the surface; this means there are pinholes on the surface which can lead to poor barrier.
The image on the right, shows the oneBARRIER coating configuration; it shows a sufficient coating film formation which minimizes surface roughness. Looking at the bottom SEM cross-section image, the coated layer has a uniform distribution which leads to stable barrier, it has a smooth primer layer and no pinholes. It is imperative to apply the correct coating weight and application method to cover the fibrils on the surface. Too little coating weight and the surface can be roughened so finding the right balance of coating weight and application method is essential.
Figure 3 shows the barrier properties of the paper using different coating methods to apply the primer; this is done with a Dye Penetrant test. On the left, is the non-coated paper sample; the red dye penetrates through the entire layer. Five different coating methods were studied, see below as A, B, C, D and E; the dye penetrant was then checked together with the OTR.
With Methods A and B, there are red dots on the reverse side meaning there are pinholes in the coated layer so the required barrier levels cannot be achieved. Method C has a similar coating weight to B but has no pinholes and the barrier is significantly improved. With the oneBARRIER primer, there are no pinholes and an OTR of less than 0.1 cm³/(m² d) is achieved immediately after the primer is applied and is by far the best method.
oneBARRIER FibreCycle Creation: Metallization
After the primer is applied, vacuum metallization is performed, the structure in Figure 4 shows that this layer can either by opaque (produced using our AluBond process) or transparent (produced using our AlOx process), both processes are performed on an EXPERT K5.
After metallization, the paper is again tested for pinholes using the same test as mentioned earlier in this article. The dye penetrant is applied to the metallized side of the paper and subsequently the reverse side is investigated for the dye leaking through. The test results can be seen in Figure 5; the same results are found before and after metallization which indicates the pinholes are in the primer layer. The metallization which is in the nm range cannot cover pinholes in the primer layer which is in the micron range.
Tests have also been conducted on the durability of the paper using a fold test. This test is to simulate the production of packaging such as a three-side sealed pouch with a bottom fold. The test was conducted before and after the application of a heat seal coating on top of the metallized layer. Without heat seal, the OTR after folding various greatly, this shows that the OTR can be drastically impacted by folding; the WVTR which is mainly associated with the metallization layer is less impacted by folding. Once the heat seal is applied, OTR and WVTR are maintained after folding which demonstrates that the heat seal coating enhances fold resistance of the metallized paper structure.
The oneBARRIER FibreCycle structure was also assessed in terms of recyclability using the PTS method. Two criteria were assessed: the disintegrateability and the undisturbed sheet formation. The test showed that the oneBARRIER structure is easy to disintegrate and that no stickies or optical inhomogeneities were found meaning that the structure is recyclable.
oneBARRIER FibreCycle for a mono-material high barrier paper alternative
oneBARRIER FibreCycle offers a mono-material paper based alterative to plastic-based flexible packaging and is recyclable. The solution utilizes the synergies between wet dispersion coating and dry vacuum coating to achieve high-performance packaging solution. FibreCycle delivers a high barrier paper-based solution with barrier performance of OTR < 1 cm³/(m² d) & WVTR < 1 g /(m² d)