A breakthrough in sustainable packaging: an industry first mono-material metallised retort solution

Packaging Solutions

The packaging industry has made great strides in recent years towards more sustainable recycle ready packaging. From the development of new mono-material polymer based packaging materials, and alternative fibre or plant based packaging, to the application of more advanced recycling technologies, great progress has been made in the journey towards a truly circular economy.

However, important gaps remain. One significant example is the lack of mono-material recyclable retort solutions for the food and beverage industry. Retort packaging is a type of durable, flexible pouch, which undergoes a high temperature sterilisation process after being filled and sealed – making the food commercially sterile and shelf stable. It has the great benefit of enabling food to be stored at room temperature for extended periods without refrigeration.

Because retort pouches must protect food from oxygen and moisture ingress and withstand high heat exposure during the sterilisation process, they are typically made of multiple layers bonded together, such as polyethylene terephthalate (PET), aluminium foil, and polypropylene (PP) to form a laminate structure. However, this makes retort packaging almost impossible to recycle. Until now.

Three industry leaders – Bobst, Brückner and Mitsui Chemicals – have now joined forces to create a world first: a mono-material, recyclable, retort solution with high barrier properties based on opaque metallisation.

Nick Copeland, research and development director, barrier solutions at Bobst, Willi Lindemann, specialist I line coating, new technologies at Brückner, and Anrika Heermant, senior specialist at Mitsui Chemicals Europe, discuss how the new solution was developed and the potential impact it could have for the packaging industry.

Can you introduce what the new solution is and why it is so important?

Nick: It is a novel mono-material retort solution with high barrier properties based on special opaque metallisation, which will be easily recyclable in existing recycling streams. It is important because recyclable retort packaging is one of the final key challenges in sustainable flexible packaging. Together, we have achieved a very important milestone, demonstrating that our solution can withstand the retort process and maintain high barrier qualities. Now, if we can take this solution through the final stages of development, it could have a significant impact for the packaging industry and on wider sustainability targets.

Why is it so challenging to develop a recyclable retort solution?

Anrika: Up until now, it has only been possible to maintain a high barrier in retort solutions using a composite layer structure consisting of polyester, aluminium foil, and various other materials. The most challenging part of producing a mono-material retort solution is maintaining the barrier qualities after the retorting process, which happens under really high temperatures.

Willi: The perception in the industry was that it couldn’t be done. It was generally assumed that metalised films could not be used for retort purposes without corrosion, because the high temperatures involved would lead to water ingress. The other challenge with moving to mono-material polypropylene is the risk of shrinkage, which would have a negative impact on the barrier properties. So, there was a lot to contend with.

Can you talk about the innovation involved and how each partner contributed to this success?

Nick: Ultimately, we needed to create an ultra thin, stretchable, heat resistant barrier primer in combination with advanced opaque metallisation. When we talk about in line coated ultra thin layers and state of the art extrusion and orientation technology, that is exactly what Brückner can bring to the table. When it comes to advanced metallisation, Bobst has significant expertise in this area. And Mitsui has the capabilities and innovation to be able to develop a novel heat resistant primer. So together, we had exactly the right expertise to develop this solution.

Willi: Brückner was responsible for the inline coating technology. We know that achieving a very thin metal receptive layer can be the key to sustainable barrier packaging. Through our innovative technology, we can stretch the primers and create very thin layers. We needed to find exactly the right hardness of the coating material to ensure it was both stretchable and could withstand the retort conditions. Ultimately, we found a solution with ideal structure.

Nick: The reels produced by Brückner in Germany on the in line coating pilot line were then delivered to Manchester in the UK for Bobst’s vacuum coating technology. We utilised the Bobst Expert K5 vacuum metalliser with AluBond technology, which is a novel vacuum metallising technology with three key benefits – it improves the barrier, improves the adhesion, and maintains the surface energy over time. So, the combination of the extremely thin in line coating together with extremely thin metallisation achieves the high barrier performance, but on really thin layers, maximising the percentage of mono-material in the structure. It was also very beneficial being able to test the in line coated metallised material in our competence centre in Manchester with our process experts available on hand. ​

Anrika: At Mitsui, we contributed two key materials to the solution. The first is a water based polyurethane dispersion called Takelac. We provided a top coating grade, which enhances the barrier performance and protects the Alubond layer. And a newly developed Takelac Primer grade, which provides the heat resistance suitable for retort applications. In addition, we provide Admer, which is a grafted polyolefin resin with good adhesion qualities. ​

How effective is the new solution?

Anrika: We have achieved proof of concept. We have demonstrated that by combining in line coating, vacuum metallisation and special resins and coatings, we can create a recyclable solution that withstands the retort process and maintains its barrier qualities. We have tested the Oxygen Transmission Rate (OTR), the Water Vapor Transmission Rate (WVTR) and adhesion levels before and after the retort process and achieved excellent results.

Is the new solution ready to use? What kind of products will it be suitable for?

Willi: While we have achieved a huge milestone, we haven't finished the development of the solution yet. There is still some work to do before this solution can become commercially available. But we are well on the right road. The next step may be to bring in further partners to ensure the solution is robust, repeatable, and production proof.

In terms of the type of food this solution could be used for, it is really any retort food – that is, food that is sterilized within the packaging. A good example is wet pet food.

What impact could this have on the industry?

Anrika: It is too early to speculate on the potential impact, but there is no question that the industry needs solutions like this. Companies will need to comply with sustainability guidelines such as the Packaging and Packaging Waste Regulation, meaning for example that mixed materials will no longer be permissible for wet pet food in the retail setting. So, we are aiming to fulfil an urgent unmet need.

Why has this partnership worked so well?

Nick: It is exactly the right combination of expertise and each company is really the leader in their respective fields, which makes it a very pioneering initiative and one where there is full trust and respect on all sides.

Each company also has all the required elements to help make this happen, meaning; well equipped laboratories, technology centres or competence centres, and dedicated process experts which has made accelerating the development of this solution providing faster time to market.

I know I speak on behalf of the entire team when I say that we are eager to keep pushing boundaries together and look forward to showcasing what is next.

From left to right: Daisuke Suzuki, director, Polyurethanes coating materials department at Mitsui Chemicals, Willi Lindemann, specialist in line coating, new technologies at Brückner, Nick Copeland, research and development director, barrier solutions at Bobst and Anrika Heermant, senior specialist at Mitsui Chemicals Europe.