Automotive OEM Coatings Market
Axalta Coating Systems Examines How Lightweight Multi-Substrate Body Design and
Low Bake Coatings Are Drivers for Innovation and a Challenge for Coating Technology
By Dr. Klemens Bartmann, Global Director Technology OEM for Axalta Coating Systems
Driven by a strong move
towards sustainability, vehicle body design is going
through a radical change.
In response to this, Axalta
Coating Systems has been looking at
ways to meet the challenges that these
new lightweight materials are presenting.
Increasing pressure from regulatory
bodies has been put on the automotive
industry to move towards more sustainable materials and processes. Over several decades, regulatory requirements,
such as reduction of organic solvent
emission, overall CO2 reduction and increased fuel efficiency, have prompted
the coatings industry to develop new,
ecologically sustainable coatings, like
high solids or waterborne materials, and
consolidated systems such as primerless,
two-wet or three-wet systems. In order to
reduce the overall weight of the car body,
the OEMs want to increase the usage
of lower weight materials, including aluminium and magnesium and polymeric
substrates. Paint shop processes and materials need to be adapted accordingly. In
the case of polymeric substrates, the baking temperatures for the coating hardening processes need to be lowered.
The lightweight materials help to cut
down CO2 emissions in the paint shop,
as energy consumption can be reduced
when using low bake materials. These
materials also offer enhanced styling
capabilities due to new opportunities in
part and vehicle geometry. The possibility
of on-line and in-line coating of body and
plastic parts means there is an opportunity to improve color harmony and to simplify the supply chain complexity.
However, these lightweight substrates
will create challenges when it comes to
coating technologies. For instance, new
adhesion processes need to be devel-
oped, which can impact on the baking
of adhesives and coatings. Long-term
durability and re-coatability of lower bake
systems must also be ensured. Overall
appearance of the final finish, which may
cover various different substrates and
lines, must be harmonised.
However, there are already some solutions in place for low bake coatings.
These include well-established processes
with a multitude of technologies and substrates used for: automotive plastic parts,
heavy duty trucks that require an increasingly demanding appearance and high
quality levels from low bake primers and
topcoats, and specialized OEMs where
low bake mixing systems provide small
batches of customer-specific ‘tie colors’.
Nevertheless, additional solutions and
processes are still needed to meet the
challenges presented by the newly-creat-ed, diverse mix of substrates.
Of the various paint technologies
feasible for low bake systems, each has
advantages and challenges. With UV curable systems, the bake window can be
brought down to ambient temperature,
but there can be problems from radiation
shadow zones. These may be avoided by
mounting UV lamps on robots that can
reach all areas and ensure proper curing.
This solution could be used in combination with a three-wet or primer-less water-borne system, offering the opportunity to
reduce overall clearcoat oven length by
up to 70 percent.
Other crosslinking technologies, such
as 2K Epoxy Acid, 2K Acrylic/Melamine
with unblocked catalyst or 1K Acrylic/
Melamine with blocked catalyst, have the
potential to reduce bake temperatures
close to the target but can have other issues, such as stability or technological
properties with these curing conditions. So
far, the leading cross-linking technology
for low bake coatings is 2K Polyurethanes.
Another option is the (Poly) Aspartate
chemistry, which is accessible through a
straight-forward synthetic procedure. It
shows promising results in achieving very
good technological properties like du-
rability and chemical resistance, even at
ambient curing temperature through very
fast cross linking reaction. This also gives
the possibility of formulating higher solids
coatings to combine the benefits of lower
bake and lower solvent emissions.
Last but not least, there is another challenge in lowering the curing window for
electrodeposition coating, as there will still
be significant metal components in future
body design. The route to lower bake ED
coatings can be described in three developmental stages. The first is a target bake
of T max on the exterior at 180oC, which
would mean minimum required temperatures of 165oC -170oC. This could contribute to energy reduction in the paint shop.
Axalta has had positive results based on
current commercialised Aqua EC4027
technology with which it has achieved
good solvent resistance and corrosion results down to 10 minutes at 150oC.
The next stage in development could
reach the temperature area (T max =
140°C) enabling on-line coating of specif-
ic plastic parts – in other words, metal and
plastic pasts can be run through the ED
bath and top coated on-line. Here there is
the need for new cross-linking chemistry
and a significant development of process
and materials. The issue of higher tem-
perature requirement for bake hardening
steel would also need to be addressed.
The potential benefits of a further
reduction of ED baking temperatures,
down to 80oC -125oC for instance, would
need to be proven – this would, however,
be a longer-term development process.
Lightweight body design will inevitably
driver further innovation in the area of low
bake coatings, materials and processes.
And while some technology is already
available, more is being developed that
will address the challenges that the new
materials present. The critical next step will
be further integration of single solutions -
materials, processes and application - in
real mass manufacturing environments.
