Note: Descriptions are shown in the official language in which they were submitted.
WO 00/62961 PCTIUSOO/06442
REINFORCED PROFILE EXTRUSION ARTICLES
AND METHOD FOR MAKING THE SAME
BACKGROUND OF THE INVENTION
Profile extrusion molding is a popular method for producing continuous
uniform thermoplastic items having often complex cross sections for use as,
for
example, automobile exterior trim. The profile assumes the shape of the
extrusion die
of choice, and is cut and end-capped to form such articles as body side
moldings. A
single profile may be designed to fit many models of cars, making profile
extrusion a
1 o popular after market process. A wide processing range of thermoplastic
materials
permits high outputs in profile extrusion. Continuous operation of an extruder
permits uniform production of plastic products. The temperature required along
the
extruder barrel, adapter and die depend upon the specific extrusion process
being
conducted and the nature of the plastic used.
In a typical extrusion process, resin pellets are either gravity fed or force
fed
from a hopper into single or twin screw extruders and are conveyed along the
screw
surface. Solid and liquid additives, such as reinforcing additives and
fillers, are often
incorporated into the mix, and must be homogenously combined via distributive
or
dispersive mixing by the screw. Additives, however, can increase the viscosity
of the
polymer melt, thereby impairing the rate of extrusion. Additives that are
difficult to
disperse may be precompounded with molten polymer into pelletized
concentrates.
However, many such additives do not achieve even distribution throughout the
melt,
creating profile products having defects, such as uneven color or unreinforced
points
susceptible to stress.
Glass fibers are commonly used as reinforcing agents in conventional
extrusion processes. Cut glass fibers may be added to the polymer melt, often
at
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levels as high as 30% by weight. As the melt flows along the screw flight,
these
anisotropic glass fibers tend to align themselves parallel to the extrusion
barrel in the
direction of flow. Consequently, the resultant profile is unidirectionally
strong in the
longitudinal aspect. The plane transverse to the longitudinal direction is
relatively
weak, and thus relatively more prone to fracture upon impact. In addition, if
the
added glass fibers are not evenly dispersed during mixing of the melt, the
degree of
longitudinal strengthening of the profile will vary. Uneven, unidirectional
reinforcement of this nature is highly undesirable in profile extrusion
products used.
To overcome the disbursement problems associated with extrusion utilizing
glass fiber, the process of pultrusion was developed. Pultrusion is
characterized by
pulling continuous glass strands through a tube containing a polymer matrix,
thereby
forming a reinforced continuous length rod having a constant cross section. A
significant drawback to pultrusion is the unexpected presence of voids or
channeling
within the reinforced rods, due to entrapment of air bubbles during the
pulling
process. Extruded articles having such voids have low impact resistance and
are
susceptible to fracture.
Therefore, a need exists for improving the impact resistance of extrusion
molded articles for use as, for example, automobile exterior trim.
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SUMMARY OF THE INVENTION
An object of the invention is to provide a profile extrusion molded product
having nearly uniform reinforcement in all aspects. The profile is formed from
a
material comprising at least one thermoplastic, and about 2% to about 15%, by
volume, of reinforcing particles. The particles each comprise one or more
layers,
wherein at least 50% of the reinforcing particles are less than about 20
layers thick, at
least 99% of the reinforcing particles are less than about 30 layers thick,
and the
layers comprise platelets having a thickness of between about 0.7 nm and 1.2
nm.
Profiles comprising essentially homogeneously dispersed reinforcing particles
in the
given amounts have a uniformly reinforced cross section.
It is a further object of the invention to provide a method of manufacturing a
highly reinforced extrusion molded part that is equally reinforced in all
aspects as
discussed above. In accordance with this object, the present invention
provides a
method of producing a reinforced article comprised of a continuous extrusion
profile
having good strength in all directions. The method prepares a melt of at least
one
thermoplastic, having about 2% to about 15%, by volume, of reinforcing
particles.
The particles each comprise one or more layers. At least 50% of the
reinforcing
particles are less than about 20 layers thick, at least 99% of the reinforcing
particles
are less than about 30 layers thick, and the layers comprise platelets having
a
thickness of between about 0.7 nm and 1.2 nm. The thermoplastic and
reinforcing
particles are intimately mixed via the rotational action of at least one screw
housed in
an extrusion barrel. The melt, including 2%-15% by volume reinforcing
particles, is
conveyed under pressure along the surface of at least one screw to a metering
section
from whence the melt is forced to exit through a shaping die at the
discharging end of
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the extrusion barrel. The discharged portions of the melt are then cooled and
cut to
desired lengths.
These and other objects of the invention can be more fully appreciated from
the following detailed description of the preferred embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
A preferred embodiment of the present invention is described herein with
reference to the drawings wherein:
FIG. 1 is side view of a single screw extruder having a shaping die for
profile
formation.
FIG. 2 is a cross-sectional view taken through a belt-line window molding
shown installed on a vehicle door in accordance with the principles of the
present
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
During extrusion, resin pellets are fed from a supply depot to a hopper loader
for collection in a receiving hopper 110, as depicted in FIG. 1. Pellets exit
the hopper
110 through a feed throat 112 into the barrel 114 of an extruder. The resin
pellets are
plasticized in the melting section 122 of barrel 114 via the rotating action
of at least
one screw 116 extending the length of the barrel. Energy from the drive motor
118 is
transferred via viscous energy dissipation through the screw 116 to the
pellets, and
heat is applied through the barrel walls, thereby melting the resin. The
polymer melt
thus formed is conveyed along the screw 116 to the compression section 124 of
the
barrel 114. Typically, the flight depth of the screw 116 decreases in the
compression
section 124 to facilitate mixing of the molten polymer into a homogenous melt.
The
melt front flows from the compression section 124 to a metering section 126.
which
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directs the melt through an exit port shaping die 120 located in the
discharging end
128 of the extruder barrel 114.
Single screw extruders may be used, although counter rotating twin-screw
extruders are better able to generate the high pressure needed in certain
profile
extrusion applications. In general, co-rotating twin screws can give excellent
mixing
while subjecting all melt material to essentially the same shear and
temperature
conditions. Preferably, the melt is subjected to dispersive mixing at a
minimum of
critical shear stress.
The articles (and the plastic melt from which the articles are molded)
according to the present invention comprise a composite material of a polymer
having
dispersed therein reinforcement fillers in the form of very small mineral
reinforcement particles. The reinforcement filler particles, also referred to
as
"nanoparticles" due to the magnitude of their dimensions, each comprise one or
more
essentially flat platelets. Generally, each platelet has a thickness of
between about
0.7-1.2 nanometers. The average platelet thickness is approximately 1
nanometer.
The preferred aspect ratio of the reinforcement particles, which is the
largest
dimension of a particle divided by the thickness of the particle, is about 50
to about
300. At least 80% of the particles should be within this range. If too many
particles
have an aspect ratio above 300, the material can become too viscous for
forming parts
in an effective and efficient manner. If too many particles have an aspect
ratio of
smaller than 50, the particle reinforcements will not provide the desired
reinforcement
characteristics. More preferably, the aspect ratio for each particle is
between 100-
200. Most preferably at least 90% of the particles have an aspect ratio within
the 100-
200 range.
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The platelet particles or nanoparticles are derivable from larger layered
mineral particles. Any layered mineral capable of being intercalated may be
employed in the present invention. Layered silicate minerals are preferred.
The
layered silicate minerals that may be employed include natural and artificial
minerals.
Non-limiting examples of more preferred minerals include montmorillonite,
vermiculite, hectorite, saponite, hydrotalcites, kanemite, sodium
octosilicate,
magadiite, and kenyaite. Mixed Mg and Al hydroxides may also be used. Various
other clays can be used, such as claytone H.Y. Among the most preferred
minerals is
montmorillonite.
To exfoliate the larger mineral particles into their constituent layers,
different
methods may be employed. For example, swellable layered minerals, such as
montmorillonite and saponite are known to intercalate water to expand the
inter layer
distance of the layered mineral, thereby facilitating exfoliation and
dispersion of the
layers uniformly in water. Dispersion of layers in water is aided by mixing
with high
shear. The mineral particles may also be exfoliated by a shearing process in
which
the mineral particles are impregnated with water, then frozen, and then dried.
The
freeze dried particles are then mixed into molten polymeric material and
subjected to
a high sheer mixing operation so as to peel individual platelets from multi-
platelet
particles and thereby reduce the particle sizes to the desired range.
The polymer composites of the present invention are prepared by combining
the platelet mineral with the desired polymer in the desired ratios. The
components
can be blended by general techniques known to those skilled in the art. For
example,
the components can be blended and then melted in mixers or extruders. The
ratios
will be determined based on, for example, desired dimensional stabilization
and/or
desired mechanical properties of the final molded article.
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An additional advantage that accrues in accordance with the present invention
is that reinforced articles of thinner profiled cross sections can be
extruded.
Particularly, articles that are reinforced with glass fibers have cross
sectional
dimensions that are limited by the relatively large dimensions of the glass
strands.
Typical glass fibers have a diameter of about 6-20 microns. In contrast, the
articles
molded in accordance with the present invention can be made with cross
sections that
are as thin as enabled by the particular thermoplastic being used, having the
desired
loadings of nanometer-sized reinforcement particles as discussed herein. Thus,
reduced areas of cross-sectional thickness can be achieved in the extrusion
process of
the present invention compared with profiles reinforced by conventional means.
If
desired, standard glass reinforced resins may be further reinforced by the
inclusion of
nanometer-sized reinforcement particles according to the invention. Such
combinations of reinforcing materials permits conventionally produced articles
to
have some improvement in transverse strength and toughness.
The typical product formed by profile extrusion is an elongated product, such
as vehicle side moldings, and generally has a constant cross section
throughout its
longitudinal extent. Some shaping of the hot melt exiting the extrusion die
may be
performed and is well known in the art. The most common form is the embossing
of
the surface to a grained appearance, such as various leather or wood-type
grains.
The appearance of the extruded profile may be altered by adhering materials to
the profile before the shaped melt significantly cools. Accordingly, the
invention
contemplates a decorative film laminated to at least one surface of an
extruded
reinforced profile. Examples of such decorative films include metallic foils
and
laminate wood textures. Lamination may be achieved by standard processes known
in the art.
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Additional specific preferred methods, for the purposes of the present
invention,
for forming a polymer composite having dispersed therein exfoliated layered
particles
are disclosed in U.S. Pat. Nos. 5,717,000; 5,747,560; 5,698,624; and WO
93/11190.
Furthermore, additional background information is disclosed in the following
U.S.
Patent Nos. 4,739,007 and 5,652,284.
Generally, extrusion processes are preferred for certain high volume
applications of reinforced plastics. Automotive exterior trim parts produced
by profile
extrusion molding can be long, continuous pieces having a uniform cross
section.
Uniformly reinforced molded-profiles for automotive trim may be produced by
extrusion according to the invention. Reinforced body side molding, rails on
luggage
racks and even luggage racks themselves may be made as well. Reinforced tie
down
rails on pick up truck boxes are also contemplated according to the invention.
Such
reinforced molded articles exhibit excellent strength, modulus range, impact
resistance
and dimensional stability and are suitable for use on an automobile exterior.
Extruded reinforced article produced according to the invention also include a
variety of sealing systems for doors and windows, as depicted in FIG. 2.
Inclusion of
reinforcing nanoparticles in the resin melt will substantially enhance
stiffness of thin
sealing system components. Such reinforced sealing members may exhibit good
stiffness without compromising the flexibility and toughness needed for
withstanding
repeated raising and lowering of windows or opening and closing of doors. The
added
strength afforded by reinforcing nanoparticles will permit thinner, better
conforming
shapes to be extruded, which will enable noise reduction due to better sealing
properties.
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Typical resins used in profile extrusion molding include nylon, polypropylene,
thermoplastic polyester and polvcarbonate. The process permits use of recycled
materials, such as scrap polyolefins. Preferably, the thermoplastic used in
the present
invention is a polvolefin or a homogenous or copolymer blend of polyolefins.
The
preferred polvolefin is at least one member selected from the group consisting
of
polypropylene, ethylene-propylene copolymers, thermoplastic olefins (TPOs),
and
thermoplastic polyolefin elastomers (TPEs). For high performance applications.
engineering thermoplastics are most preferred. Such engineering thermoplastic
resins
may include polycarbonate (PC), acrylonitrile butadiene styrene (ABS), a
PC/ABS
blend, polyethylene terephthalates (PET), polybutylene terephthalates (PBT),
polyphenylene oxide (PPO), thermoplastic polyurethanes (TPU) or the like.
The exfoliation of layered mineral particles into constituent layers need not
be
complete in order to achieve the objects of the present invention. The present
invention contemplates that more than 50% of the particles should be less than
about
20 nanometers in thickness. Otherwise stated, more than about 50% of the
particles
should be less than about 20 platelets stacked upon one another in the
thickness
direction. In addition, at least 99% of the particles should have a thickness
of less
than about 30 layers. Preferably, at least 90 % of the particles should have a
thickness
of less than about 5 layers. It is most preferable to have as many particles
as possible
to be as small as possible, ideally including only a single platelet.
Particles having
more than 30 layers may behave as stress concentrators and are preferably
avoided, to
the extent possible.
Generally, in accordance with the present invention, each of the automotive
parts that can be manufactured in accordance with the principles of the
present
invention should contain nanoparticle reinforcement in amounts less than 15%
by
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volume of the total volume of the part. The balance of the part is to compnse
an
appropriate thermoplastic material and optionally, suitable additives. If
greater than
15% by volume of reinforcement filler is used, the viscosity of the
composition can
become higher than what is desirable for molding. Preferably, the amount of
reinforcing nanoparticles is greater than 2% by volume, as lower amounts would
not
achieve the desired increase in strength.
Preferably, relatively rigid profile extrusion molded exterior trim parts
comprise reinforcement particles of the type described herein at about 2-15%
of the
total volume of the part, with the balance comprising the thermoplastic
substrate. It is
1 o even more preferable for these exterior trim pieces to have reinforcement
particles of
the type contemplated herein comprising about 3%-8% of the total volume of the
part.
For some applications, inclusion of about 3%-5% by volume reinforcing
nanoparticles
is optimal.
When about 90% of the reinforcing nanoparticles in the composition are less
than 5 nm in thickness, a more preferred unifonn distribution of the particles
throughout the resin is achieved, which translates into homogeneous
reinforcement
throughout the molded profile. The extremely small size of these reinforcing
particles
permits intimate mixing without damaging the particles. A reduction to near
elimination of unreinforced areas in cross section occurs in the final
extruded profile,
accordingly.
Reinforced profiles produced according to the invention have good impact
resistance and exhibit 2-4 times the modulus of traditionally reinforced
articles
without losing strength. Unlike profiles reinforced with glass fibers, the
inventive
profiles are strong and stable in the XYZ dimensions, and are not limited to
unidirectional reinforcement. This is primarily due to the greater uniformity
of
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distribution and smaller aspect ratios of the nanoparticle reinforcements of
the present
invention in comparison with conventional glass fibers. Therefore, profiles
extruded
according to the invention have good impact resistance in a plane transverse
to the
longitudinal direction. Specifically, impact resistance in the transverse
plane is
generally at least 80% of the impact resistance in the longitudinal direction
90
degrees to the transverse plane.
In addition to reinforcing agents, other additives may optionally be included
in
the polymer composition to improve processability. For example, aging
modifiers,
such as glycerol monostearate, are useful additives in polymer compositions
for
molding. Aging modifiers are typically present in an amount from about 0.5% to
about 5% thermoplastic resin. Other additives include pigments, heat
stabilizers.
antioxidants, flame retardants, ultraviolet absorbing agents and the like.
Reinforced articles of the invention exhibit improved properties over non-
reinforced articles. For example, polyethylene articles having about 5%
nanoparticles
by volume, wherein 90% of the particles have 5 or fewer layers, increased
flexural
modulus by 2.5 to about 3 times over compositions lacking reinforcing
nanoparticles,
as measured under ASTM D790 test conditions. This 5% nanoparticle polyethylene
article exhibited > 200% elongation to rupture. By contrast, about 25-30%
glass fiber
reinforcement is required in such articles to achieve an equivalent modulus.
Reinforced polymer articles according to the invention should show from at
least 50%
to 60% improvement in flexural modulus over articles lacking reinforcement
nanoparticles. Thus, the use of reinforcing nanoparticles according to the
invention
provides articles having good flexural stiffness.
A particularly advantageous application of the present invention relates to
the
area of window moldings.
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FIG. 2 is a cross-sectional view taken through a belt-line window molding 10
shown installed on a vehicle door in accordance with the principles of the
present
invention. As shown, the main body 11 includes a seal member or seal structure
30,
and a door mounting structure 50. The door mounting structure has rigid
interior
support structure 18, preferably made of aluminum. Steel, hardened plastic, or
other
rigid material can also be used. The support structure 18 includes a
substantially flat
plate portion 20, which is constructed and arranged to extend downwardly
between
the door body 12 and the vehicle window, which window is represented generally
in
broken-line configuration by reference numera122. The support structure 18
further
includes an upper bent portion 24 extending from the plate portion 20 and is
constructed and arranged to bend over the joint between the inner door panel
16 and
outer door panel 14. The support structure 18 then extends downwardly from the
bent
portion 24 to flange portion 26 thereof. In essence, the support structure 18
has an
inverted-J cross-sectional configuration.
Support structure 18 is imbedded along its entire extent within the seal or
member 30 and the door mounting structure 50, as shown. The seal member 30 and
door mounting structure 50 together form the main body 11 of the window
molding
10. The upper part of plate portion 20 on the window facing side thereof, is
covered
by the seal member 30. The seal member 30 is preferably made from a flexible,
resilient material comprising at least one thermoplastic, such as a polymer
resin,
having reinforcing nanoparticles disbursed throughout. The reinforcement
particles
comprise about 2% to about 15% of a total volume of the resin part. At least
50% of
the reinforcement particles have a thickness of less than about 201avers, and
at least
99% of the reinforcing particles have a thickness of less than about 30
layers.
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As discussed above, substantially all of the platelet layers have a thickness
of
between about 0.7 nm and 1.2 nm. The reinforcing particles are essentially
homogeneouslv dispersed throughout the thermoplastic such that the seal member
30
has a uniformly reinforced cross section. As a result, impact resistance
and/or tear
resistance in the transverse plane is generally at least 80% of the impact
resistance in
the longitudinal direction 90 degrees to the transverse plane.
Seal member 30 preferably includes an upper seal portion 32 and a lower seal
portion 34, which portions extend generally between the door body 12 and the
window 22 to prevent external elements, such as rainwater, from entering
between the
door body 12 and window 22. The underside of the upper sea] portion 32 and the
underside of the lower seal portion 34 are provided with conventional dorrie
flock
material. indicated by reference numeral 36. The upper seal portion 32 and the
lower
seal portion 34 are constructed and anranged to flex and apply a resilient
force against
the window 22, as can be appreciated from the broken-line illustration of the
upper
seal portion 32 and lower seal portion 34. In particular, the upper seal
portion 32 and
the lower seal portion 34 force the dorrie flock material against the window,
with the
dorrie flock material providing a sliding friction seal, which permits sliding
movement of the window, but prevents rainwater from seeping between the window
22 and door body 12.
Preferably, the reinforced seal member 30, the mounting structure 50, the
dorrie flocks 36, and the support structure 18 are extruded together in an in-
line
extrusion process. After these elements have been manufactured, a cover trim
member 60 is snapped in place to cover the flange portion 40 of the mounting
structure 50 for aesthetic and protective purposes, as disclosed in
International
]3
CA 02365248 2007-07-11
Application WO 98/01313.
Because the seal member 30 is provided with the reinforcing particles as
discussed above, stiffness of the seal member 30 is enhanced, while the needed
toughness for repeated flexing as windows are opened and closed is maintained.
Modulus of reinforced resin according to the invention is increased about 1.5-
4 times
greater than that of non-reinforced resin. Repeated elongation by flexing is
increased
by more than 20%. Such characteristics will provide a reduction in wind noise
due to
better sealing and the possibility thinner, better conforming shapes than can
be
achieved using conventional sealing members known in the art.
It should be appreciated that the foregoing description is illustrative in
nature
and that the present invention includes modifications, changes, and
equivalents thereof,
without departure from the scope of the invention.
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