Paper Technology International 2020 - Journal - Page 46

PAPERTECHNOLOGYINTERNATIONAL
At the same time, we can achieve all the advantages
of plastic materials. High water, oil- and grease resistance,
low temperate and tropical MVTR, low OTR, and rapid sealing
properties. We can even add other specialty chemicals to add
further function. For example, combining with other chemical
treatments to the pulp to give internal protection from oils and fats.
When switching to more sustainable alternatives it is
important to make sure that one environmental issue is not replaced
by another. You should therefore make sure that the barrier coatings
you use are water-based dispersions and contain no VOC, solvents
or “forever” chemicals like PFAS.
Figure 4: Another way to visualize the benefits of sustainable
barriers compared to plastic based barriers.
One barrier coating doesn’t fit all
The transition from plastics to more sustainable materials
is not a straightforward task for packaging producers. It requires
a deep understanding of both the requirement for each product’s
end-use as well as the needed barrier properties. Depending on the
end-use and desired properties of the packaging materials, different
types of barrier coatings, or even a combination of barriers, can
be necessary. Therefore, we at BIM have defined the BIM Barrier
Standards.
This is a tool to help eliminate over-packaging and achieve
optimal use of resources by identifying the requirements for each
product.
To make this simple, we have divided the packaging
demands into five key properties: hydrophobicity, oil- and grease
resistance, water vapor transmission, oxygen transmission, and heat
sealing.
Let’s examine these five properties in simple language.
Hydrophobicity
Hydrophobicity is the physical property of a barrier coating
to repel a mass of water. This is important to protect a product from
water, hold liquid and moist/wet products, and to keep the paper
or board substrate dry, and preserve its structural integrity and
strength.
Strictly speaking, there is no repulsive force involved, it is
an absence of attraction. Hydrophobic barrier coatings tend to be
formulated with nonpolar components and therefore have a low
surface free energy. Water droplets on these surfaces will exhibit a
high contact angle (form a bead) as water is a polar molecule with
high surface tension.
Hydrophobic is often used interchangeably with lipophilic,
(fat-loving), however, the two terms are not synonymous. While
more hydrophobic barrier coatings are usually more lipophilic (a
trade-off of OGR performance), both properties can be combined.
Naturally, the more hydrophobic a barrier coating is, the
more difficult it is to glue with water-based adhesives or print over
with water-based inks.
Hydrophobicity is typically measured via an extended Cobb
test (900s/1800s/3600s) and variations thereof. It can also be
measured with the contact angle.
Oil- and grease resistance
Oil and grease resistance, OGR, is the ability to inhibit the
penetration of grease, oils, and fats through the barrier coating
layer and into the substrate. This is important to protect against
the accidental transfer of oil, grease, and fats from the product
or package to the user, and to stop the aesthetic spoiling of
the packaging caused by oils, grease, and fats penetrating the
substrate.
Figure 5: The BIM Barrier Standard helps us identify which properties are required. To meet the requirements up to three different
barriers can then be applied in up to three layers.
The Barrier Standards required for a packaging material
are defined by the demand placed on the barrier and the expected
packaging life term. Once the requirements are defined, we can
tailor a solution with one layer, a combination of two layers, or even
up to three layers, to create the perfect mix of properties.
Figure 6: The perfect mix of properties.
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