A range of coatings for a range of properties
An effective solution to this is to use coating layers to improve barrier properties. If the proportion of these coatings is limited to 5% of the total film structure’s weight, the material will still be classified as a mono-material and will be recyclable. These layers protect the barrier properties of film packaging from scratching, condensation, or extreme temperatures during handling or transportation. They can also deliver several other important properties.
For instance, acrylic coatings can provide sealability, which is critical for product shelf life, especially in vacuumed or gas-flushed packaging. A break in the seal can destroy the packaging’s barrier function. However, delivering strong barrier performance alongside good sealability can be difficult.
In particular, films’ outer layers must be able to withstand the high temperatures of heat-sealing jaws. Acrylic coatings of 0.8-1.0g/m2 (dry) are used to achieve this, and are particularly suitable for flexible food packaging materials.
Heat-sealable coating layers also enable sealing on stretched, biaxially-oriented polypropylene and polyester (BOPP and BOPET) film for food packaging. This allows packaging manufacturers to achieve the required strength and consistent adhesion. Typically, these layers are 0.1-0.2g/m2. Additionally, primers are always required with heat-sealable coating layers.
Coatings that provide aroma and odor barriers play another important role in mono-material solutions for food packaging. Some food products, such as chocolate, need to be prevented from picking up external odors that impair their taste. For others, such as coffee and spices, it’s important to maintain their own aroma. Typically, uncoated BOPP film does not provide a sufficient aroma and flavor barrier; nor do most standard heat-seal resins, so specialized coating resins must be used.
Additional coating layers can also protect against mineral oil migration in food packaging. Migration of contaminants from packaging to food is a well-known issue in folding board packaging, but also poses a risk in flexible packaging.
In particular, mineral oil migration from print on the front of packaging has been known to contaminate dry food products like cereal, pasta, and rice – and some of these oils are classified as carcinogens. PE and BOPP do not form sufficient mineral oil barriers, so packaging manufacturers must use extra layers to keep food safe.
In laminated materials, adhesives also play an important part in optimizing packaging for the environment where it will be used. They can be polyurethane, acrylic, or natural rubber latex adhesives, or non-PE- or non-PP-based tie-layers. Observing the maximum coating weight limit is particularly important in adhesives to avoid gel formation during extrusion, which reduces recyclate quality and blocks screen filters on the extrusion line.
From six layers to four
To meet the growing need for recyclable packaging – and therefore, for high-performance mono-material solutions – DSM has developed several coating resins that provide these properties. They form thin, functional coatings that are suitable for many applications, including flexible packaging and film. In line with Ceflex guidelines, these coatings can replace thicker material layers to help ensure that flexible and film packaging can still be recycled and reused.
Our mono-material portfolio includes resins for layers including primers, topcoats, and lamination adhesives. These resins deliver a strong barrier performance by providing sealability, heat resistance, and protection from odor and mineral oils.
They also offer a range of additional key properties, including anti-blocking, adhesion, printability, transparency, surface enhancement, and food contact compliance. They can be used on a range of film and flexible packaging substrates, including BOPP, BOPE, BOPET, and polylactic acid (PLA).
With these mono-material solutions, the number of layers in a piece of flexible packaging, such as a packet of chips, can be reduced from six to four. The six-layer structure would typically contain a PE or cast polypropylene (CPP) sealing layer, an adhesive, an aluminum inner layer, a second adhesive layer, ink, and a PET or OPP surface layer.
By contrast, a four-layer structure using our mono-material solutions would contain a sealing layer, BOPP film, a protective aluminum oxide layer, a sealable layer, and ink. In this way, these solutions open new possibilities not just for recyclable packaging, but for a more circular packaging industry.
A sustainable packaging future ahead
From the manufacturing process to printing and end-of-life, all of these innovations can help deliver a world of more sustainable packaging. Indeed, a combination of solutions must be used to improve the environmental impact of packaging at every stage of its lifecycle. For this, companies must work together across the value chain to deliver renewable packaging materials, safe printing processes, and components designed for recyclability.
At DSM, we are continually developing additional solutions through our core research program, and actively seek co-creation opportunities with partners and customers in the packaging sector. Above all, it’s clear that, with more and more promising technologies being developed, a bright packaging future is certainly possible.