Paper Technology International 2024 - Journal - Page 129
PAPERTECHNOLOGYINTERNATIONAL
the 昀椀lling good inside include, for example; barriers against water, oil
and grease, as well as against acids, bases, or alcohol, depending
on the packed product. So, the requirements for functional coatings
always depend on the intended use of the packaging, whether it
comes into direct contact with sensitive 昀椀lling goods, such as food,
the environmental conditions it is exposed to along the supply chain
and, of course, the shelf life of the packaged goods. Just look at a
paper cup that needs to be impervious to liquids, a cheeseburger
wrapper that needs to be resistant to grease, a pouch of coffee that
needs to maintain aroma, a tray of fruit that needs to be resistant to
water and a cement sack that needs to withstand moisture vapour.
In some cases, a single barrier type is suf昀椀cient, but in
most packaging applications a combination of several properties is
required. This also includes the extension of the barrier performance
of a coating with sealability – a very important attribute for many
packaging converting processes – or adding another coating, for
example; with slip or a anti-slip function to facilitate downstream
converting on a 昀椀lling line, or supply chain demands such as
palletization.
Effective paper barriers with full recyclability
As one of the world’s leading manufacturers of printing inks
and coatings for packaging applications and labels, we at Siegwerk
know exactly what it takes to utilise functional coatings in packaging
and we work closely with industry partners to ensure our coating
solutions are designed to be compatible with material recovery
systems, especially paper recycling.
Our portfolio of water-based barrier coatings already
includes solutions for the protection of cartonboard and corrugated
board as well as 昀氀exible paper packaging materials against liquids,
oil and grease, water vapor, and oxygen. Whether used for paper
cups, fast food wrappers, corrugated boxes, sachets, pouches, or
昀氀ow packs, they all meet the functional needs of the application,
such as; barrier performance, 昀氀exibility, and sealability, without
compromising recyclability, and where it makes sense, also
compostability.
Take for example the resistance to liquids - one of the most
important requirements for barrier coatings when it comes to 昀椀berbased packaging due to the hydrophilic nature of most papers and
boards. Whether it’s a hot or cold, acidic, or oily liquid, the packaging
needs to keep 昀氀uids in, or out effectively. However, water is also a
key part of the 昀椀ber recovery process, so we need to 昀椀nd the right
balance between using coatings to enable packaging performance
without preventing repulpability. At Siegwerk, we have a dedicated
team of experts constantly developing and optimizing our coating
solutions and looking for the best ways to ensure we support
circularity in the 昀椀ber-based packaging value chain.
Figure 2: Examples of successful transition from plastic to
昀椀ber-based packaging alternatives are appearing the market,
and in the media, what feels like everyday.
Critical factors for using barrier coatings
As discussed, there are many factors that needs to be taken
into consideration when developing and using functional coatings for
昀椀ber-based packaging, let’s look a bit deeper into some of these for
achieving barrier performance.
For example, the selected base paper or board is very
important, more precisely its technical characteristics such as
porosity, smoothness, homogeneous 昀椀ber structure, internal
sizing, surface sizing, and surface coating, are all parameters to
be considered. Another critical factor is choosing the right coat
weight; a higher coating laydown usually means a better barrier
effect but requires more drying capacity and can increase the risk
of blocking which can negatively impact downstream converting,
or even damage the barrier. In general, a lower web temperature
and minimum coat weight can reduce the risk of blocking. Suf昀椀cient
drying is also crucial for good barrier performance as the drying
method (e.g. hot air, IR, etc.) and the drying conditions have a
signi昀椀cant impact on the coating performance. Here, temperature
range and 昀椀nal moisture content are key to ensure a dry surface
and a balanced internal paper/board moisture. Other critical factors
include the use of pre-coating, primer, or multi-layer application,
as well as the selection of the right coating application system to
achieve a homogenous coverage without defects and a fully closed
昀椀lm surface.
In summary, it is always important that the barrier coating
is aligned with the paper or board substrate to be coated, as well
as the planned end-use application, and also the coating, printing,
and converting equipment to be used. Therefore, at Siegwerk when
we start working on a barrier coating project with a customer, we
always examine the substrate in detail 昀椀rst, check the existing
machinery options, verify the possibility for customizing the coating,
and the opportunity to add additional products to further bene昀椀t the
converting process.
Figure 4: Considerations for achieving good converting
Figure 3: Considerations for achieving good barrier performance. performance.
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