■ ADDITIVES
This automobile door handle made from glass fiber
filled polyamide has improved scratch resistance
and surface finish through
the use of a specially developed siloxane additive
High Quality and Permanently
Scratch Resistant
Surfaces. Even after years of use polypropylene surfaces in vehicles should look
like new. In order to meet this tough requirement various polypropylenes were
treated with specially developed additives based on siloxanes. Compounds manufactured in this way give component parts exceptionally good and in particular
permanent scratch resistance. The experience gained with these additives in
polypropylene has also been applied to engineering plastics such as polyamide,
PMMA and PC/ABS blends.
KATHRIN LEHMANN
nybody buying an automobile today expects the interior of their vehicle to look as good as new even
after many years of use.A car whose dashboard or center console develops nasty
scratches after gentle knocks does not
meet these expectations. Customer satisfaction and resale value are lowered with
every scratch. Apart from that all drivers
want a high quality and appealing ambience nowadays. Accordingly plastic parts
often have a grained and matt rather than
smooth finish that in terms of both haptic and looks has to make a pleasing and
high class impression. In particular there
is a desire for grained dark surfaces that
A
is virtually independent of model, manufacturer and price and can be observed
worldwide. Figure 1 shows the dual
plaque insert from an injection molding
tool with typical grained surfaces for automobile interiors.
Plastics now account for up to 20 % of
the weight of a vehicle.From the wide spectrum of polymers polyamide (PA), acrylonitrile butadiene styrene copolymers
(ABS), polycarbonate (PC), thermoplastic
polyurethanes (TPU) and polypropylene
Fig. 1. Dual plaque
insert from an injection molding tool for
automobile surfaces
(VW K 09 and K 31
grain structures)
Translated from Kunststoffe 9/2009, pp. 99–102
Article as PDF-File at www.kunststoffeinternational.com; Document Number: PE110176
64
© Carl Hanser Verlag, Munich
Kunststoffe international 9/2009
ADDITIVES ■
(PP) are just some of the
ones used in vehicle construction. There are several ways to make polymer
surfaces scratch resistant.
One of these involves the
use of high performance
polymers such as polyamide or ABS, which are
however relatively expensive. Alternatively, the surfaces can be additionally
coated, although this degree of effort can only be
justified in the premium
model sector.
In contrast, with mid- Fig. 2. The flow properties of the compounds can be determined
range and compact auto- by measuring the spiral flow length
mobiles every cent saved
per kilogram compound counts. For this have to be on the one hand light, mereason low cost polypropylene is gener- chanically stable and cheap and on the
ally used which gains the necessary other grained and as scratch resistant as
strength through the addition of up to possible. Grained and scratch resistant are
20 % talc as filler (PP talc compounds). at the first glance two properties that are
TPOs (thermoplastic polyolefins) are of- difficult to combine with each other. This
ten also added to such compounds to im- is because the grain has a serious disadprove both the mechanical properties as vantage: Finger nails, ball point pens or
well as the look and feel of the surface car keys can more easily catch in the fine
(PP/TPO talc compounds).
structure than on a smooth surface and
so a grained surface is getting scratched
Cost Effective, Grained and
more easily. Additives are often used to
Scratch Resistant
minimize these effects so that pointed objects can more easily glide across the surA permanent scratch resistant polypropy- face.
lene with an attractive price/performance
Normally in order to make talc filled
ratio represents a substantial challenge for PP materials scratch resistant additives
manufacturers of plastic parts for vehicle such as amides, silicone oils or grafted
interiors. Door handles, dashboards, polymers are used. However, many of
bumpers, door panels and center consoles these additives do not confer a long last-
ing solution. Long term tests show that
these materials have a relatively high fogging potential. Thus sooner or later the
component part will lose its scratch resistance. In addition many of the additives are not odorless and vehicle passengers can feel disturbed by the volatile
components. Silicone oils and amides also migrate to the surface and form oily
stains or result in a sticky haptic. Grafted
polymers and additive combinations of
these substances migrate less, but are
more expensive than straight amides. On
top of this, they negatively affect the flow
properties of the compound during injection molding of the part. The flow
properties are typically investigated using
a flow spiral (Fig. 2) since the determination of the MFI (Melt Flow Index) is not
sufficient.
A new additive from the Consumer
Specialties business unit of Evonik Goldschmidt GmbH, Essen, Germany, now
promises to put this right. The organically modified siloxane Tegomer AntiScratch 100 does not exhibit the disadvantages of conventional additives and also offers an attractive price/performance
ratio. In order to study the influence of
various raw material parameters in the
formulation, a number of compounds
based on PP and PP/TPO were produced
in which the particle size and content of
the talc as well as the quantity of the modified siloxane were varied. Fundamentally, the smaller the particle size of the talc
the better the scratch resistance is. On top
of this grey talc grades produce less white
scratches than white, often very fine talcs. V
Fig. 3. Various instruments for the determination of scratch resistance (top) and the resulting scratch and mar pattern (bottom)
Kunststoffe international 9/2009
65
■ ADDITIVES
Mechanical Properties
Scratch Resistances
Scratch resistance DL with 10N
2,000
MPa
1,900
E-Modulus
Unmodified
Tegomer AntiScratch 100
1,800
Oleamide
1,700
Grafted polymer
1,600
1,500
3.5
4.0
4.5
5.0
5.5 kJ/m2 6.0
10
8
6.5
6
4.9
4
3.4
1.9
2
0
Unmodified
Oleamide
Charpy notched impact strength at -20 °C
© Kunststoffe
Grafted
polymer
Tegomer
AntiScratch 100
© Kunststoffe
Fig 4. Comparison of the mechanical properties of three 20 % HTP 1 standard talc filled PP/TPO compounds, with additives such as 0.5 % amide,
3 % grafted polymer and 3 % Tegomer AntiScratch 100 (left) as well as corresponding scratch resistances (right)
The instruments available at Evonik to
measure scratch resistance, shown in Figure 3, make it possible to conduct tests
that are well established at automobile
manufacturers and compounders. One of
the most important is the Erichsen test in
which a fine diamond pattern is engraved
into the surface using a steel needle subject to various loads (5 to 30 N depending on the polymer).
In all the scratch tests the talc in the
PP/TPO played a decisive role. This is because the deeper the scratch, the greater
the difference in lightness between the
dark surface and the exposed talc on the
scratched surface. This difference can be
measured as a Delta L value, created from
the brightness difference between a
scratched and non-scratched surface. The
depth of the line can be measured using
CLSM (Convocal Laser Scanning Microscopy). Naturally materials with high
levels of talc (up to 40 %) are particularly susceptible and even light scratches can
be clearly seen.
Multiple Demands on Additives
It can be seen that newly developed additives have to satisfy multiple demands.
Firstly they must be able to provide immediate scratch resistance for the materi-
i
Manufacturer
Evonik Goldschmidt GmbH
Goldschmidtstr. 100
D-45127 Essen
Germany
Tel. +49 201 173-2824
Fax +49 201 173-1889
www.evonik.com/plastic-additives
66
Fig. 5. Special talc treatment by IMI FABI Talc Company, determination of the contact angle and the
resulting wetting of the hydrophobic contact area of the special grade with SEM (scanning electron
microscope)
al so that the component part does not become damaged during transport or assembly. For this reason scratch resistance
is measured 24 h after injection molding
the test piece. In the long term, however,
the scratch resistance has to be guaranteed
even after many years of use, which is important for the end customer. Therefore
the component part is held in a climate
chamber for 7 days at 70 to 80°C and ageing tests at 120°C check the deterioration
in the mechanical properties. The additive
has to be effective in various formulations
for the widest possible range of talc and
TPO contents and, regardless of the surface graining, a low Delta L value in the
Erichsen test has to be guaranteed.
The results with Tegomer AntiScratch 100 are very encouraging in all respects. The siloxane additive does not migrate, which is due to the positive interaction between the PP and the organic
side chains of the siloxane. Components
based on this newly developed antiscratch additive are therefore odorless and
do not display any glossing or an oily appearance of the surface. The scratch resistance is expected to be retained over the
entire life cycle of the product.
Scratch Resistant with as Little
as 2 to 3 % Additive
The investigations have shown that PP
compounds with 3 % Tegomer AntiScratch 100 have particularly small
Delta L values both in short as well as
long term tests. Fig. 4 shows this for the
scratch resistance of a PP/TPO compound with 20 % talc alongside the key
mechanical properties. In this case HTP1,
a typical talc grade from IMI FABI Talc
Company, Postalesio, Italy, was used. It
can clearly be seen that 3 % Tegomer AntiScratch 100 makes it possible to achieve
a Delta L value of less than 2 and improved notched impact strength without
loss of elasticity.
To further improve the PP/TPO talc
compound in respect of scratch resistance
© Carl Hanser Verlag, Munich
Kunststoffe international 9/2009
ADDITIVES ■
IMI FABI has produced a specially treated talc grade. Fig. 5 illustrates how the application of a special coating to a standard
talc makes it more hydrophobic, which
the significantly lower contact angle
shows.As a result improved wetting of the
talc surface by the polymer can be seen in
the corresponding SEM picture (scanning
electron microscope) of the special grade.
Looking at the relevant mechanical properties and in particular the scratch resistance of the PP/TPO formulation discussed in Fig. 4, the picture shown in Figure 6 emerges. In comparison to the standard grade IMI FABI HTP1 the special
talc grade IMI FABI NS 140 shows not only an improvement in the scratch resistance of the surfaces K09 and K31, which
Fig. 7. Scratching of a high gloss PC/ABS surface with the Crockmaster (2,000 strokes/9 N),
where 2 % Tegomer M-Si 2650 results in a clear improvement in scratch resistance
ness at injection molding companies with
automobile applications (e.g. air bag covers and center consoles) and then, where
appropriate, optimize the formulation in
Comparison of Talc Grades
Fig. 6. Scratch resistance and mechanical
properties of PP/TPO
compounds with 20 %
talc. Comparison of
the standard talc
grade HPT1 and the
special talc grade
NS 140, each with
3 % Tegomer AntiScratch 100
Flexibility
110
100
Scratch
resistance
K 09
Charpy notched
impact strength
at 23 °C
90
80
70
60
50
Scratch
resistance
K 31
IMI FABI HTP1
IMI FABI NS 140
MFI
Charpy notched
impact strength
at -20°C
HDT
at 1,820 kPa
© Kunststoffe
are relevant for VW, but also an improvement in notched impact strength
(Charpy impact strength at 23°C and at
-20°C). This means that there is a large
optimization potential for future compound development. The developer is not
limited to selecting the talc grade in terms
of the required target mechanical parameters and scratch resistance, but can
also, by combining this with 2 to 4 % of
Tegomer AntiScratch 100, achieve an excellent level of scratch resistance without
negatively affecting the haptic and odor
of the compound.
partnership with OEMs and compounders.
The insights gained with the use of
siloxane additives in PP were then also
evaluated in PC/ABS blends, PMMA and
PA. Here it was more appropriate to test
high gloss polymer surfaces for example
with the Crockmaster which results in the
scratch patterning seen in Fig. 7. As an
example in the test the PC/ABS blend
with 2 % Tegomer M-Si 2650 was virtually undamaged even after 2,000 strokes
at 9 N. This shows that the Crockmaster
allows a significantly better differentiation of the compounds compared to the
otherwise more common pencil hardness
test.
The siloxane additive Tegomer AntiScratch 200 has been developed for polyamide applications which alongside improvements in the scratch resistance of
glass fiber filled polyamide compounds
also improves the flow properties during
the injection molding process so that even
dark colors can be realized without surface problems, i.e. fewer glass fibers with
unwetted ends oriented to the surface,
caused by unintentional fiber breaks. It is
therefore particularly interesting for applications such as automobile door handles (Title picture) and other high quality items. ■
THE AUTHORESS
KATHRIN LEHMANN, born in 1967, is head of application technology and development for additives in
plastics and polymer applications at Evonik Goldschmidt, Essen, Germany;
Kathrin.Lehmann@Evonik.com
Market Potential and
Know-How Transfer
Since the siloxane additive is particularly
easy to distribute in comparison to other
technologies it is possible to conduct initial injection molding tests without prior
compounding. In the supply chain it was
therefore possible to assess the effectiveKunststoffe international 9/2009
67