'Anti'-finish automotive leather - Performance Chemicals

Technology | Automotive leather
‘Anti’-finish automotive
leather – vision and
contradiction
By Dr Brigitte Wegner and Dr Gerhard Wolf, BASF SE
Car manufacturers have been paying increasing attention
to automotive interiors in recent years because they are
seeking to distance themselves from their competitors
and to create a specific image for their brand. Consumers are
encouraged to treat the interior of their vehicles like their own
living room, with an individual design and high standards of
comfort and serviceability.
As many different materials are used in automotive interiors
leather is in competition with textiles, synthetics, Alcantara etc.
The question here is what distinguishes leather from other
materials, and the simple answer is the natural feel and natural
appearance. It is this feature that is primarily responsible for
leather’s image as a luxury, premium-grade material. Leather will
have to retain its natural character if it is to defend its position in
the market, but this conflicts with the market’s demands for other
features such as resistance to abrasion, etc.
BASF’s ‘anti’-finish concept for automotive interiors is an
approach that makes it possible to pursue a long-term vision for
automotive leather while, at the same time, fulfilling the shortterm
demands of original equipment manufacturers (OEMs). In
finishing, the aim must always be to retain the natural character
of the leather, ideally by dispensing with the finish altogether or,
at least, by reducing the amount of finish or making it invisible.
The underlying premise is that applying less finish or ‘anti’-finish
adds more value to the leather.
These demands are certainly not easy to satisfy, but they
represent the current trend in the market for automotive leather
in Europe and increasingly in North America and Asia. The goal
of the leather industry has to be to develop ‘anti’-finishes that
will maintain and enhance the image of leather as a premium-
Figure 1. Requirements
38
Challenge
Comfort
Design
Ecology
OEM-Specs
Competition by
other materials
Long term
BASF - Anti-Finishing
‘Anti....as you want’
Short term
Vision
Daily
work
quality material. Improved seating comfort, a better feel and
visual appearance are important arguments. Manufacturers along
the whole leather value chain should have a vital interest in
developing this ‘anti’-finish concept for automotive interiors. But
as well as pursuing a long-term vision, manufacturers also need
to pay attention to the short-term, daily demands of the OEMs.
Apart from the visual appearance and feel of the leather, most
demands concentrate on physical fastness and serviceability.
These demands can be summarised under the prefix ‘anti’, ie
anti-squeak, anti-soiling, anti-hydrolysis and anti-abrasion. As
shown in figure 2 this can be further extended and ecological
demands can also be illustrated with ‘anti’ terms like antiemission,
anti-RSL (restricted substance list), anti-CO2 and antideforestation.
BASF’s ‘anti’-finish concept can be applied flexibly
according to what is demanded. There is often no ideal solution
but at least it illustrates the problems and unresolved issues and
makes a solution easier to find.
‘Anti’-squeak
There has been a large reduction in the overall noise level of
motor vehicles in recent years. This has prompted increasing
demands, especially from manufacturers of premium brands in
Europe, to eliminate the interior noise caused by squeaks. It
remains to be seen whether other manufacturers in Asia and
North America will follow suit in the future.
Squeaks are caused by friction between leather and other
surfaces in the interior of the vehicle, including the driver. The
BASF Novomatt system with its special additives has proved to
be very effective for eliminating squeaks.
Figure 3 shows a comparison between standard leather and
Figure 2. ‘Anti’-finishing
Anti-RSL
Anti-tox
Anti-emission
Anti-CO2/-CF
Anti-waste AAnti-deforestation
Anti-squeak
Anti-overspray Anti-energy
‘Anti....as you want’
Anti-soiling
Anti-???
Anti-Finishing
Anti-hydrolysis
A ti h d l i
Anti-shrink
Anti-abrasion
Anti-ageing
A
Anti-’polishing’
LEATHER INTERNATIONAL | www.leathermag.com July 2011

less squeaky leather tested with a Stick Slip Tester according to
VDA 230-206. The smaller the deflection of the oscilloscope, the
less friction is generated and there is less noise.
‘Anti’-soiling
There is also a general trend away from black leather trim towards
brighter, more attractive colours, and this will increase in future.
This trend reflects the move towards more individualised vehicle
interiors, such as using brighter colours. Therefore, one of the
most frequently discussed problems is how to make leather more
resistant to soiling and easier to clean, and it is also one of the
most difficult problems to solve. First, because ‘each’ OEM has
their own ideas about soiling and their own specifications. The
second reason is that the chemical structure of all the different
types of soil can vary widely from fatty, hydrophobic soil such as
butter and ketchup etc, through to hydrophilic soil such as coffee
and dyes. The leather also has to be resistant to inorganic soil
such as soot, dust and silicates and to organic soil such as urine,
blood and saliva. The chemical bonds that all these different types
of soil form with the surface of the leather can be very diverse.
These range from simple adhesion, via ionic bonds and hydrogen
bonds through to stable covalent bonds.
There is no single effective solution to the problem of
improving the soiling resistance of leather and making it easier to
clean. Therefore, BASF offer customers an ‘anti-soiling toolbox’
consisting of products with a wide range of different chemical
structures. Figure 3 shows the results obtained in the Martindale
test (VDA 230-212) as an example.
‘Anti’-abrasion
Abrasion is a recognised problem, especially the wear caused to
seats by passengers. Generally leather is more resistant to
abrasion if the finish is hard and smooth and applied as thickly as
possible. However, this contradicts the trend towards natural
leather and the concept of ‘anti’-finish systems. Abrasion
resistance is a particularly important topic for OEMs in Japan and
the US. This is reflected in the wide variety of test methods, such
as the Gakuschin (Japan), Wyzenbek (US) and Taber methods (US,
Asia, EU). The Taber, Ball Plate and Mie tests have established
themselves in Europe. Compromises have to be made and some
performance in abrasion tests will have to be sacrificed in order
to retain the natural feel of the leather.
Figure 4 shows the yellowing resistance of leather treated
with a standard finish and leather treated with an optimised
finish after 400 hours at 110°C. This is currently the most
demanding test method on the market.
‘Anti’-ageing and ‘Anti’-hydrolysis
Automotive leather is used together with other materials such as
metals and plastics in automotive interiors, and these materials are
so resistant to ageing that leather can hardly begin to compete.
Leather is a natural material and its structure makes it prone to
ageing, but specially adapted finishing systems can be developed
to improve its resistance to ageing. Very specific solutions have to
be developed for each OEM because the demands vary very widely,
as do the test methods by which these demands are assessed.
Anti-hydrolysis or the resistance of leather to ageing by
hydrolysis is a special case because it is tested at high humidity and
July 2011
Automotive leather | Technology
Figure 3. Anti-squeak and anti-soiling
Anti-squeak, slip-stick-test Anti-soiling
VDA 230-206
VDA 230-2122
Quiet
Noisy
Standard
New
Grey scale
Low Change in colour High g
2
3
4
Figure 4. Anti-abrasion and anti-ageing
Standard Standard New New
BASF �nish with Astacin® Novomatt +
Lepton® Protector
Industry standard
5
1000x
1000x
Rub cycles with denim in Martindale test
Anti-abrasion
Anti-ageing
Taber-test Heat yellowing
(DIN ( EN 14327) )
acc. to Toyota, y , 100ºC, , 400h
With
damage
Without Without
damage damage
high temperature. It can be assessed by observing changes in
colour, flexometer values, surface area, surface texture and softness.
The ageing resistance of leather depends to a significant
extent on the crust. High-quality crust has high lightfastness
and there is no migration, shrinkage or hardening under the test
conditions. It is essential that these premises be met in order to
obtain the best results. The products contained in finishes have to
remain stable, especially at high temperatures and high humidity.
Acrylic polymers and polyurethanes based on polyethers and
polycarbonates have been found to perform very reliably, and these
are marketed by BASF under their Corial and Astacin brands.
‘Anti’-emission
Reducing overall emissions from leather is a complex undertaking
with many different facets. The original reason for reducing
emissions in vehicle interiors was to prevent the windows from
being fogged by volatile substances. These efforts were then
extended to cover volatile organic carbon (VOC), and a chemical
analysis was made of the substances released in the interior of
vehicles. OEMs have been very imaginative and have devised a
whole host of test methods for volatile organic compounds with
the result that greater attention has been paid to the individual
substances that are released into the ambient air and to issues
relevant to health. The most prominent example is the discussion
concerning formaldehyde in leather, and the limits on
www.leathermag.com | LEATHER INTERNATIONAL
39

Technology | Automotive leather
Figure 5. NMP
formaldehyde have gradually been made more stringent over the
past ten years.
A more recent example is the discussion concerning Nmethylpyrrolidone
(NMP) in leather. NMP is a solvent that has
been used as an ingredient in finishing products and also directly
in production processes. The use of NMP was novel but it has
since come under pressure for toxicological reasons.
The first attempt at eliminating NMP was to replace it with Nethylpyrrolidone
(NEP). This certainly made sense from the point
of view of technology but not from the point of view of toxicology
because NEP is also not free of toxicological problems. It must be
emphasised that both solvents, NMP and NEP, can be detected
fairly easily by measuring the VOC.
Because NMP and NEP are so easy to detect, it is likely that
OEMs will set a limit of zero for these substances in their
specifications, ie below the threshold of detectability. A difference
between NMP, NEP and formaldehyde is that the sources of these
two solvents can be identified very easily and they can be replaced
with other solvents. NMP and NEP are employed in the manufacture
of finishing products for technical reasons but they are also added to
finishing formulations in order to improve their performance. BASF
have responded to this challenge and now supply a range of
products for finishing automotive leather that is completely free of
NMP and NEP.
BASF’s automotive products
Another challenge is to reduce the carbon footprint by preventing
the release of greenhouse gases, predominately CO2. These
indirect emissions are predominately caused by the consumption
of energy in the form of fossil fuels. Carbon footprint is a very
40
N-Methyl-2-Pyrrolidone
O
N
(pure product)
CH3
Formulations
> 5 to 10% NMP
10 – 20% NMP
> 20% NMP
Figure 6. NEP
NEP=N-Ethyl-pyrrolidone
O
CH2CH3
N
(pure product)
Formulations
> 1 to 3% NEP
H360D: May damage the
unborn child.
H315: Causes skin irritation
H319: Causes serious eye
irritation
H335: May cause
respiratory irritation
H360D
Hazard statements Pictograms
H315, H319, H360D
H315, H319, H360D, H335
H318: Cause serious
eye damage.
H361d: Suspected of
damaging the
unborn child.
H319: Cause serious
eye irritation.
> 3% NEP H318 and H261d
Hazard statements Pictograms
Figure 7a. BASF automotive range
Binders
Corial ® Binder DN Astacin Finish PE Astacin Finish PUM
Corial Ultrasoft NT Astacin Finish PR Astacin Finish PUMN TF
Astacin ® Ground UH TF
Top coats
Astacin Finish PS Astacin Finish SUSI TF
Lepton ® Matting EO Astacin Matting HS Astacin Novomatt GG
Lepton ® Top LC
Crosslinkers
Astacin Matting LV TF
Astacin Matting MT
Astacin Novomatt DM
Astacin Hardener CN Astacin Hardener CI Astacin Hardener CA
Figure 7a. BASF automotive range
Filters/oils/waxes
Lepton ® Enhancer CP Eukesol ® Oil Ground Lepton Wax A
Lepton Enhancer LT Luron ® Matting Lepton Filler FCG
Lepton Matting LB-F Lepton Additive TL
Lepton Matting AL
Levelling agents
Lepton Paste VL
Amolian ® VM
Handle modifiers
Amolian SW Amolian VC
Lepton Wax WN Lepton Wax DS Corial Wax TA
Lepton Protector SR Lepton Wax HM
important topic for the automotive industry because it has often
been accused of being one of the main perpetrators of global
warming and all its negative consequences. In Germany for
instance, the global warming potential of all new vehicles has to
be quoted as a CO2 equivalent value. The leather industry, in
particular manufacturers of automotive leather, will eventually be
forced to address this issue and quantify the global warming
potential of leather in the form of the CO2 equivalent value per
unit area. This is a new challenge and it is one that BASF are
intensively pursuing as part of their ‘anti’-finish concept. The
vision here is to reduce the carbon footprint by manufacturing
leather that is carbon-neutral and environmentally friendly.
Conclusion
BASF’s ‘anti’-finish concept offers a means of analysing and
structuring the many different visions and concepts for
automotive leather. Solutions have already been identified in
some areas, but intensive research and development will be
required in others until satisfactory results can be obtained. The
aim of all these efforts has to be to safeguard and foster the
image of leather as a premium-quality material with a natural
character. This is part of the overall challenge facing the leather
industry, which is to ensure that other materials do not replace
leather.
Acknowledgements
For great support the authors thank their colleagues Bernd
Schroedelsecker, Klaus Machauer, Leo Derichs and Helfried Scheid.
LEATHER INTERNATIONAL | www.leathermag.com July 2011