Note: Descriptions are shown in the official language in which they were submitted.
- 2199106
Glass matt reinforced thermoplastics suitable for the
production of paintable parts and part~ produced
therefrom
Glass matt reinforced thermoplastics (GMTs) are of
increasing interest in many branches of industry,
~pecifically in the automotive industry. In such cases,
GMTs are preferably processed by the flow molding
process, by which even complicated parts can be produced
with ~hort cycle times in just a single molding
operation. However, currently only parts which are not in
the visible area are produced from GMTs by means of the
flow molding process, ie. neither parts for interior
paneling nor exterior paneling, since the appearance of
the parts thus produced does not meet requirements. Until
now, the production of a surface equivalent to a painted
steel sheet has failed on account of two problems, to be
specific so-called surface defects and inadequate paint
a &e B ion.
In contrast to GMT fabricated by forming processes, it is
not possible with GMT processed by flow molding to pre-
fabricate a layer structure with a glass-free surface in
the semi-finished product and retain it during molding of
the finished part. The reason for this is that, in flow
molding, heated GMT, ie. an "insert" which has a much
smaller surface but greater thickness than the finished
part, is placed into a cold or moderately heated mold and
distributed by the molding pres~ure by flowing in the
mold. Any surface layers would be destroyed in this
process. It is consequently unavoidable that the surface
of the molding consists of the same GMT as in the rest of
the molding, 80 that problems with glass fibers
protruding out of the surface arise when building up the
layer of paint. Building up a layer of paint is also
disturbed by an uneven "orange peel" surface of the
molding, which i8 produced in the ca~e of GMTs known from
the prior art by the shrinkage of the matrix polymer
during cooling. A further problem for the surface is
caused by the sequence of events in the molding
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operation, in which the insert, heated outside the mold,
is placed into the cold or moderately warm mold, the mold
is then closed and only at the end of the closing
operation i8 the pressure which brings about the mold-
flowing of the GMT built up. For this reason, the ~urfaceof the insert is inevitably in contact with the mold for
much longer than the rest of the surface of the molding,
which only forms during flowing. This has the effect that
the two parts of the surface of the molding have a
different appearance, known as insert visibility, ie.
until now, with GMTs known from the prior art, it can be
seen on the molding where the insert was. One possible
way of reducing the insert visibility is to increase the
mold temperature. However, this inevitably means longer
cooling time for the molding and consequently a reduction
in the output, and resultant increased unit costs.
A further quality problem of painted GMT moldings is the
adhesion of the paint layer on the molding. This applies
in particular to GMT with a polyolefin as its matrix
polymer.
For example, using the current state of the art, the
adhesion of a paint layer on GMT with polypropylene as
its matrix polymer is unsatisfactory or can be achieved
only with high technical expenditure.
The object of the present invention was consequently to
find gla~s matt reinforced thermoplastics with which it
is ensured that firstly the building up of a paint layer
is not disturbed in any way by glass fibers protruding
out of the surface or by an orange peel effect on the
molding, secondly that no insert visibility occurs and
thirdly that on the painted part satisfactory paint
adhesion on the GMT surface is obtained without great
expenditure.
Unexpectedly, it has been possible to achieve this object
by firstly using matrix polymers of a low viscosity,
secondly by using glass matts which, upon heating, bring
_ 3 _ 21 991 ~6
about an eYp~n~ion of the GMT produced therewith to at
least 2.5 times its original thickness and, optionally,
thirdly by additionally using fine-particle, mineral
fillers.
Consequently, the subject of the present invention are
glass matt reinforced thermoplastics which are suitable
for the production of paintable parts and which comprise
a) a thermoplastic matrix polymer of a viscosity under
processing conditions correspon~;ng to a melt flow
index (MFI 230/2.16) of polypropylene of at least
250 g/10 min and
b) one or more glass matts which, upon heating, bring
about an expansion of the glass matt reinforced
thermoplastics to at least 2.5 times the original
thickness,
optionally in combination with
c) an addition of fine-particle, mineral fillers.
Suitable as matrix polymers for the GMTs according to the
invention are thermoplastics of a viscosity corresponding
to a melt flow index (MFI 230/2.16) of polypropylene (PP)
of at least about 250 g/10 min. Preferred are those
thermoplastics which have a viscosity which corresponds
to an MFI of PP of about 300 to about 1500 g/10 min,
particularly preferred of about 500 g/10 min to about
1000 g/10 min. These may be, for example, polyolefins,
polyamides, polystyrenes, polycarbonate~, polyesters,
such as for example polyethylene terephthalate or poly-
butylene terephthalate, polyether ketones, polyether
ether ketones, polyether sulfones, polyether imide~,
polyphenylene oxide, polyphenylene sulfide or poly-
sulfones or their mixed polymers. It is preferred to use
polyolefins, particularly preferred to use polypropylene
and its copolymers or mixed polymers such as for instance
PP modified with EPDM.
The corresponding matrix polymer is reinforced according
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to the invention by means of one or more glass matts. The
glass matts used are in this case processed such that, on
heating, they bring about an expansion of the reinforced
thermoplastic to at least 2.5 times the original
thickness of the reinforced thermoplastic. It is
preferred to achieve an expansion of the GMT to at least
3 times the original thickness.
Glass fiber matts are understood as meAn;ng textile sheet
materials compo6ed of glass fibers. The glass fibers may
in this case be 10 mm to infinitely long, it being
possible for the fibers or filaments to be both in random
arrangement and oriented. Fibers of 50 to 250 mm in
length are used with preference. To improve the
mechanical properties of the finished component, the
glass fibers may also contain adhesion promoters, for
example based on silane, chromium or titanium. The fiber
matts are bonded, for example, by needle-punching or by
matt consolidation by means of applying binders. Bo~;ng
is preferably performed by means of needle-punching.
The glass matts bonded by needle-punching are intended,
upon heating, to bring about an expansion of the GMT to
at least 2.5 times the original thickness. The precise
needle-pl-nch;ng parameters are in this case best
determined by prel;~;nAry tests; they depend, inter alia,
on the type of glass fibers used, their chopped length
and surface treatment, the type of nonwoven formation,
and on the characteristic geometrical variables of the
needle-punching machine.
Furthermore, the needle-punching is to be performed in
such a way as to obtain an adequate number of projecting
glass fibers, by which a furry surface structure is
achieved, whereby the insert visibility is significantly
reduced, without the surface of the GMT being disturbed
by the protruding glass fibers. This number is dependent
here on parameters for the component production, such as
for instance the size and shape of the insert and of the
finished component.
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The ratio of thermoplastic to glass fiber matt is chosen
such that the completed semi-finished product contains
between 10 and 60% by weight, preferably between 15 and
40% by weight, of glass fibers, based on the GMT. There
may be either just one matt impregnated with the polymer
melt, or el~e a plurality of matts lying one on top of
the other may be impregnated.
It is also preferred to add to the thermoplastics 2 to
60% by weight, preferably 10 to 40% by weight, of fine-
particle mineral fillers. Examples of mineral fillers forthis are talc, chalk, barium sulfate.
The particle size of the filler in this case lies between
1 ~m and 100 ~m, preferably between 3 and 50 ~m and
particularly preferably between 5 and 30 ~m. However, if
a filler i8 added, it must be ensured that the viscoRity
of the polymer contA;n;ng filler does not drop below a
value corresponding to an MFI of PP of 250 g/10 min. The
visco~ity of the polymer contA;n;ng filler should
consequently likewise correspond at least to an MFI of PP
of 250 g/10 min, preferably 300 to about 1500 g/10 min,
particularly preferably about 500 to about 1000 g/10 min.
It must also be ensured that, if a filler is added, the
proportion of the glass fiber matt in % by weight does
not fall below 10% by weight.
The GMTs according to the invention may be produced in
any desired way, for instance in accordance with a
process known from the prior art, such as for example
described in DE 23 12 816, AT 388.896 etc.
On account of their outstA~;ng surface properties, the
GMTs according to the invention are ~uitable for the
production of painted moldings, for example for the
automotive industry.
2 1 99 1 06
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ExamPle 1:
Glass fiber roving of the type EC 16 2400 from the PPG
company was cut on a chopping machine to give a chopped
fiber of 4 inches in length, deposited on a conveyor belt
as a fiber layer of 620 g/m2 and introduced on said belt
into a needle-pnnch; ng machine of the Fehrer type NL 9S
make and needle-punched with 43 punches per cm2 and a
needle penetration of 15 mm.
2 of the chopped fiber matts thus produced were fed to a
double-belt press of the ~eld make, arranged one on top
of the other in such a way that the needle-emergence
sides of the matts faced outward, ie. that of the upper
matt upward and that of the lower matt downward.
PP with a melt flow index MFI 230/2.16 of 520 (type YS 80
from the PCD company) was melted in a single-screw
extruder of the Reifenhauser type RH 1651 make and, at a
melt temperature of 205~C, applied via a slot die onto
the lower matt, running to the press at 2 m/min, the
upper matt was placed onto the layer of melt and the
matt/melt/matt assembly was fed to the double-belt press.
In the press, a pressure of 15 bar was applied to the
assembly for a total dwell time of 3 min (including
setting). A GMT of 3.7 mm in thickness, a den~ity of
1.12 g/cm3 and a glass content of 30% was obtained.
A sample piece of the abovementioned GMT was heated in a
radiation stove to 210~C and, after a dwell time of
7 min, cooled and consequently made to set. The GMT set
in the ~Yp~n~e~ state had a thickness of 15.8 mm.
3 cut-to-size pieces of 240 mm x 166 mm of the above-
mentioned GMT with a weight of 165 g each were heated inthe radiation stove in a time of 5 min to 220~C and
pre~sed together with a pressing force of 2000 KN to form
sample parts of 590 x 250 x 3 mm. The mold temperature
was 62~C. After a holding time of 65 8, the part was
removed. The insert was clearly evident visually, and
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-- 7
also could be felt slightly, on the impression of the
polished mold surface.
The abovementioned parts were treated with 2 R Primer and
2 K Filler from the Schwab Lacke company and subsequently
painted with 2R Topcoat paint from the Sherwin Williams
company.
The paint surface was visually satisfactory, ie. the
slightly different surface structure in the region of the
insert was covered by the painting.
In the subsequent tests, however, satisfactory results
were not achieved.
The cross-cut test (in accordance with EN ISO 2409) gave
the value Gt 5, ie. paint adhesion completely
unsatisfactory. The VDA stone impact test was not OK.
ExamPle 2:
GMT was prepared as in Example 1, with the change that
40% of talc A 10 from the Naintsch Mineralwerke GmbH,
Graz, company was added to the matrix polymer.
The density of the GMT obtained was 1.40 g/cm3, the glass
content was 23.8%. The GMT, set in the expanded state,
had a thickness of 15.2 mm.
The insert was just visually evident, but could not be
felt, on the impression of the polished mold ~urface.
The abovementioned parts were coated with primer in the
same way as in Example 1.
The following were achieved in the tests:
Cross-cut test Gt 0-1, ie. paint adhesion excellent to
very good.
Stone impact test OR.
