U.S. patent application number 10/950826 was filed with the patent office on 2005-05-05 for composites containing crosslinkable thermoplastic and tpv show layer.
Invention is credited to Cothran, Liggett, Kim, Henry, Pauli, Timothy N..
Application Number | 20050095374 10/950826 |
Document ID | / |
Family ID | 36119552 |
Filed Date | 2005-05-05 |
United States Patent
Application |
20050095374 |
Kind Code |
A1 |
Cothran, Liggett ; et
al. |
May 5, 2005 |
Composites containing crosslinkable thermoplastic and TPV show
layer
Abstract
Methods for forming a composite for use as a vehicle weather
strip and the products formed thereby are disclosed in which a main
body member is formed from an elastomer polymer and an abrasion
resistant decorative layer including a blend of a crosslinkable
thermoplastic polyolefin and a thermoplastic vulcanizate is applied
thereon. The crosslinkable thermoplastic polyolefin preferably
includes a crosslinkable olefin homopolymer. The olefin homopolymer
preferably contains grafted silane functional groups to allow the
material to be crosslinked in the presence of moisture. The
abrasion resistant decorative layer may be extruded or otherwise
applied onto the main body either prior to or after the main body
member is cured and either prior to or after the crosslinkable
polyolefin of the abrasion resistant decorative layer is
crosslinked. The material of the abrasion resistant decorative
layer may be extruded into sheet form and laminated onto the main
body member.
Inventors: |
Cothran, Liggett;
(Lambertville, MI) ; Kim, Henry; (Canton, MI)
; Pauli, Timothy N.; (Stratford, CA) |
Correspondence
Address: |
FAY, SHARPE, FAGAN, MINNICH & MCKEE, LLP
Seventh Floor
1100 Superior Avenue
Cleveland
OH
44114-2518
US
|
Family ID: |
36119552 |
Appl. No.: |
10/950826 |
Filed: |
September 27, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10950826 |
Sep 27, 2004 |
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09912099 |
Jul 24, 2001 |
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6828011 |
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Current U.S.
Class: |
428/31 ;
264/174.11 |
Current CPC
Class: |
B29K 2021/00 20130101;
B29C 63/044 20130101; B29L 2031/30 20130101; B60J 10/17 20160201;
Y10T 428/31855 20150401; B29K 2009/00 20130101; B29L 2031/26
20130101; Y10T 428/26 20150115; Y10T 428/266 20150115; Y10T 428/269
20150115; B29C 48/09 20190201; B29K 2023/06 20130101; B32B 2307/554
20130101; B32B 2383/00 20130101; B60J 10/16 20160201; B32B 27/32
20130101; B32B 25/08 20130101; B29C 48/18 20190201; Y10S 428/926
20130101; B29C 48/21 20190201; B29K 2009/06 20130101; B29K 2023/16
20130101; B29K 2995/0087 20130101; B32B 2323/04 20130101; Y10T
428/31663 20150401; B32B 25/14 20130101; B32B 2319/00 20130101;
Y10S 428/923 20130101; B29C 48/49 20190201; B29L 2031/265 20130101;
B29K 2301/10 20130101; B32B 2307/746 20130101; B29C 48/001
20190201; B60J 10/80 20160201; B29K 2105/24 20130101; B29C 48/155
20190201; B60J 10/265 20160201; B29C 48/0016 20190201; B29C 48/304
20190201; B32B 2323/16 20130101; B29C 48/022 20190201; B29C 48/12
20190201; Y10T 428/31909 20150401 |
Class at
Publication: |
428/031 ;
264/174.11 |
International
Class: |
B32B 025/00 |
Claims
What is claimed is:
1. A method for forming a composite suitable for use as a vehicle
weather strip, the method comprising the steps of: providing an
elastomer polymer; forming a weather strip main body member from
said elastomer polymer; providing a blend of a crosslinkable
polyolefin and a thermoplastic vulcanizate; forming an abrasion
resistant decorative layer from said blend; contacting said
abrasion resistant decorative layer with said main body member; and
at least partially crosslinking the crosslinkable thermoplastic
polyolefin of the blend, thereby forming said composite
extrusion.
2. The method according to claim 1, wherein the step of providing
said blend is performed by providing a blend of a moisture
crosslinkable olefin homopolymer and a thermoplastic vulcanizate
comprising a crosslinked elastomer and a polyolefin, and further
wherein the step of at least partially crosslinking said
thermoplastic polyolefin is performed by immersing said abrasion
resistant decorative layer in a water or steam bath.
3. The method according to claim 2, wherein said moisture
crosslinkable olefin homopolymer is a silane grafted
polyethylene.
4. The method according to claim 2, wherein said blend comprises
from about 75% to about 87% by weight of said TPV and from about 9%
to about 15% by weight of said crosslinkable polyolefin.
5. The method according to claim 1, wherein said elastomer polymer
is a thermoset elastomer rubber.
6. The method according to claim 5, wherein said thermoset
elastomer rubber is an EPDM rubber.
7. The method according to claim 5, further comprising the step of
at least partially curing said elastomer polymer of said main body
member.
8. The method according to claim 1, wherein the steps of forming a
weather strip main body member is performed by extruding said
elastomer polymer and the step of forming an abrasion resistant
decorative layer is performed by extruding said blend.
9. The method according to claim 8, wherein the step of extruding
said main body member is performed utilizing an extrusion
temperature of about 110.degree. C.
10. The method according to claim 8, wherein the step of extruding
said abrasion resistant decorative layer is performed utilizing an
extrusion temperature of from about 200.degree. C. to about
260.degree. C.
11. The method according to claim 7, wherein the step of at least
partially curing said elastomer polymer is performed utilizing a
temperature of from about 180.degree. C. to about 270.degree.
C.
12. The method according to claim 7, wherein the step of contacting
said abrasion resistant decorative layer with said main body member
is performed after said elastomer polymer is at least partially
cured.
13. The method according to claim 8, wherein the steps of extruding
said elastomer polymer and extruding said blend are performed by
simultaneously extruding said elastomer polymer and said blend
through a common extrusion die.
14. The method according to claim 13, further comprising the step
of at least partially curing said elastomer polymer, and further
wherein the step of at least partially crosslinking said
crosslinkable thermoplastic polyolefin of said abrasion resistant
decorative layer and the step of at least partially curing said
elastomer polymer of said main body member are performed subsequent
to the step of simultaneously extruding said elastomer polymer and
blend through a common extrusion die.
15. The method according to claim 1, wherein the step of forming
said decorative layer is performed by extruding said blend as a
sheet member.
16. The method according to claim 15, further comprising a
lamination step wherein said sheet member is laminated to said main
body member by use of an embossing wheel.
17. The method according to claim 1, wherein the thickness of said
abrasion resistant decorative layer is from about 0.1 to about 1.5
mm.
18. The method according to claim 17, wherein the thickness of said
abrasion resistant decorative layer is about 0.5 mm.
19. The method according to claim 1, wherein said blend further
comprises a slip agent.
20. The method according to claim 19, wherein said slip agent is a
siloxane slip agent.
21. The method according to claim 20, wherein said siloxane slip
agent is present in said blend in an amount of from about 2-5% by
weight.
22. The method according to claim 19, wherein said composite has a
static coefficient of friction of between 1.2 and 1.6.
23. The method according to claim 19, wherein said composite has a
dynamic coefficient of friction of between 1.8 and 2.1.
24. A method for forming a composite extrusion suitable for use as
a vehicle weather strip, the method comprising the steps of:
providing a thermoset elastomer rubber; forming a weather strip
main body member from said thermoset elastomer rubber at a
temperature about 110.degree. C.; providing a blend of a
thermoplastic polyolefin comprising a crosslinkable olefin
homopolymer and a thermoplastic vulcanizate having a shore A
hardness of about 30 to about 50; forming an abrasion resistant
decorative layer from said moisture crosslinkable thermoplastic
polyolefin at a temperature of about 200.degree. C. to about
260.degree. C. having a static coefficient of friction of from
1.2-1.6; contacting said abrasion resistant decorative layer with
said main body member; at least partially crosslinking the olefin
homopolymer by exposing the abrasion resistant decorative layer to
a water or steam bath at a temperature of about 60.degree. C. to
about 110.degree. C.; and at least partially curing said thermoset
elastomer rubber by heating said main body member to at least the
cure temperature of said thermoset elastomer rubber, thereby
forming the composite extrusion.
25. A wear resistant composite suitable for use as a vehicle
weather strip comprising an abrasion resistant decorative layer,
wherein said abrasion resistant decorative layer comprises a blend
of an at least partially crosslinked polyolefin and a thermoplastic
vulcanizate, the abrasion resistant decorative layer bonded to and
disposed immediately adjacent an elastomer polymer main body
member.
26. The composite according to claim 25, wherein said crosslinked
polyolefin is a moisture crosslinkable silane grafted
polyethylene.
27. The composition according to claim 25, wherein said wherein
said blend comprises from about 75% to about 87% by weight of said
TPV and from about 9% to about 15% by weight of said crosslinkable
polyolefin.
28. The composite according to claim 25, wherein said elastomer
polymer is a thermoset elastomer rubber.
29. The composite according to claim 28, wherein said thermoset
elastomer rubber is an EPDM rubber.
30. The composite according to claim 25, wherein said abrasion
resistant decorative layer is a sheet member.
31. The composite according to claim 30 wherein said sheet member
is laminated and bonded to said main body member.
32. The composite according to claim 25, wherein the thickness of
said abrasion resistant layer is from about 0.1 to about 1.5
mm.
33. The composite according to claim 32, wherein the thickness of
said abrasion resistant layer is about 0.5 mm.
34. The composite according to claim 25, wherein said abrasion
resistant decorative layer comprises a slip agent.
35. The composite according to claim 25, wherein said slip agent
comprises a polysiloxane.
36. The composite according to claim 35, wherein said layer has a
dynamic coefficient of friction of between 1.8 and 2.1.
37. A wear resistant composite suitable for use as a vehicle
weather strip comprising an abrasion resistant decorative layer
comprising a blend of a crosslinked thermoplastic polyolefin, a
thermoplastic vulcanizate, and a slip agent, bonded to an at least
partially cured thermoset elastomer rubber main body member,
wherein said abrasion resistant decorative layer has a static
coefficient of friction of between 1.2 and 1.6.
38. A wear resistant composite according to claim 37, wherein said
slip agent comprises a polysiloxane.
Description
[0001] The present application is a continuation-in-part
application of U.S. Ser. No. 09/912,099, filed Jul. 24, 2001.
BACKGROUND
[0002] The present exemplary embodiments relate to a process for
forming molded or extruded composites and the products formed
thereby, particularly automobile weather strips. They finds
particular application in conjunction with vehicle weather strip
composites comprised of an elastomeric polymer and a show layer
including a thermoplastic vulcanizate and a crosslinked
thermoplastic polyolefin, and will be described with particular
reference thereto. However, it is to be appreciated that the
present exemplary embodiments are also amenable to other like
applications.
[0003] It is common in the motor vehicle industry to fashion
decorative abrasion resistant sections for various parts of an
automobile by extruding or molding such sections from certain
thermosetting polymeric materials. Examples of typical abrasion
resistant sections manufactured by such a process include colored
weather strips. These weather strips are mounted on an automobile
door surface and along the perimeter of automobile doors to provide
a seal between the door and the automobile body as well as to
protect both the door and exterior objects when they come in
contact with each other. Weather strips are typically molded or
extruded and attached to a vehicle by an adhesive tape or by
mechanical means such as by crimping or the use of fasteners.
[0004] Various thermoset elastomeric rubber materials, such as
ethylene propylene diene terpolymer (EPDM), styrene-butadiene
copolymer (SBR) and chloroprene rubbers have been commonly used to
form these weather strips. These materials are favored by
manufacturers because they are relatively inexpensive compared to
thermoplastics and generally exhibit both the desired flexibility
necessary for providing an effective seal and acceptable
weatherability properties. However, these elastomers typically lack
the low-friction, abrasion resistance, and weatherability that is
necessary at the point of contact with the exterior for extended
life of the weather strips. In addition, it is difficult to impart
desirable surface color and gloss to such materials.
[0005] Manufacturers have therefore attempted a variety of
approaches to improve the wear resistance, aesthetics and other
properties of elastomeric sealing sections. One strategy for
weather strips has been to apply a second layer of low friction
polymer to selected surfaces of the elastomeric weather strip,
particularly along an area that is exposed to the exterior.
Incorporated within the second layer can be various pigments or
dyes such that the surface of the weather strip matches the color
of the automobile.
[0006] Depending on the composition of the main body of the weather
strip, this second layer is often formed from polyvinyl chloride
(PVC) or an uncured non-polar thermoplastic elastomer, such as
polypropylene or polyethylene. These second layers are usually
applied directly to the weather strip surface by lamination or as a
solvent-based spray, or after an application of a primer or
adhesive layer to the elastomer. However, these methods are not
completely satisfactory. In addition to longer processing time and
added material cost, it is difficult to obtain a satisfactory bond
between the elastomer and the surface coating. Sprayed on coatings
are prone to cracking while an adhered layer is susceptible to
peeling.
[0007] Another method that manufacturers have used to adhere the
second layer to the extruded weather strip is to cohesively bond a
layer of wear resistant thermoplastic to the weather strip. Several
techniques have been developed to accomplish this. According to one
method, the elastomer rubber and the second layer are co-extruded.
The resulting composite is then passed through an oven in which the
elastomer rubber is cured and the interface between the second
layer and the rubber is heated to such a degree that the second
layer partially melts, causing it to adhesively bond with the
rubber. Alternately, the rubber is extruded first and passes
through an oven in which it is at least partially cured. A molten
thermoplastic is then extruded onto the vulcanized rubber. The
residual heat of the rubber as it emerges from the oven promotes
interdiffusion of the two layers at the interface between the two,
forming a bond between the two materials.
[0008] Due in part to the uncrosslinked nature of the
thermoplastic, however, it is difficult to control exactly the
degree of melting that the second layer undergoes in this
technique. If the second layer melts too much, the abrasion
resistance it affords may be compromised and its aesthetic appeal
diminished. Thus, there is a need for a new vehicle weather strip
composite that overcomes the deficiencies and limitations of the
prior art.
BRIEF SUMMARY OF THE INVENTION
[0009] In a first embodiment, there is provided a process for
forming a composite automobile weather strip including a main body
member of elastomeric polymer and an abrasion resistant decorative
layer, the abrasion resistant decorative layer including a blend of
a crosslinkable polyolefin and a thermoplastic vulcanizate.
[0010] The use of a crosslinkable TPO allows a manufacturer to
maintain the desirable qualities associated with thermoplastics
while affording greater control of melting and alleviating other
processing concerns. The crosslinkable polyolefin may contain
grafted silane functional groups. In the presence of moisture,
water hydrolyzes the silane. Under the action of a catalyst, the
resulting silanol groups then condense to form intermolecular
crosslinking sites. The thermoset elastomer rubber may be cured by
sulfur or peroxide agents.
[0011] In a second embodiment, there is provided a wear resistant
composite suitable for use as a vehicle weather strip including an
abrasion resistant decorative layer, wherein the abrasion resistant
decorative layer includes a crosslinkable olefin polymer and a
thermoplastic vulcanizate, bonded to and disposed immediately
adjacent an at least partially crosslinked elastomer polymer main
body member.
[0012] The versatility of the abrasion resistant decorative layer
allows it to be applied to the elastomer member in several ways. In
a first preferred technique, the olefinic polymer/TPV blend is
co-extruded with an uncured thermoset elastomer rubber main body
member and then exposed to water to crosslink the olefinic polymer.
The resultant composite is then passed through an oven to vulcanize
the thermoset elastomer rubber main body member. In a second
preferred technique, the olefinic polymer/TPV blend, is step
extruded onto a previously cured or partially cured thermoset
elastomer rubber main body member. The crosslinkable olefinic
polymer in the blend is then crosslinked by immersion in a water
bath, or otherwise exposed to moisture. In a third preferred
technique, the olefinic polymer/TPV blend is extruded into a sheet
or tape form and laminated onto a previously cured or partially
cured thermoset elastomer rubber main body member. The resulting
composite is then subjected to a water bath, or otherwise exposed
to moisture, to crosslink the grafted silane groups in the olefinic
polymer. Alternately, the elastomer member and/or the olefinic
polymer/TPV blend are molded heat bonded to each other.
[0013] While all the techniques produce acceptable results, if
olefinic polymer/TPV blend is applied to the elastomer main body
prior to the curing of the main body member, the olefinic polymer
should preferably be crosslinked before the elastomer main body
member is cured. This is to ensure that the decorative layer does
not melt excessively during the subsequent heating.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a cross section of a preferred embodiment weather
strip for a vehicle in accordance with the present invention.
[0015] FIG. 2 is a depiction of a first preferred technique of the
present invention for manufacturing a composite extrusion suitable
for use as weather strip for a vehicle.
[0016] FIG. 3 is a depiction of an alternative preferred technique
of the present invention for manufacturing a composite extrusion
suitable for use as a weather strip for a vehicle.
[0017] FIG. 4 is a depiction of an another alternative preferred
technique of the present invention for manufacturing a composite
extrusion suitable for use as a weather strip for a vehicle.
[0018] FIG. 5 is a flowchart depicting the main processing steps in
the first preferred technique of the invention detailed in FIG.
2.
[0019] FIG. 6 is a flowchart depicting the main processing steps in
the second preferred technique of the invention detailed in FIG.
3.
[0020] FIG. 7 is a flowchart depicting the main processing steps in
the third preferred technique of the invention detailed in FIG.
4.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0021] The present invention provides a variety of sealing strips,
weather strips, glass run channels, etc. for vehicles. As used
herein, the term "weather strip" is used to refer broadly to any
such strips conventionally used in automobiles and other vehicles.
Briefly, the weather strips preferably comprise at least two
components, each formed from particular materials and having a
unique cross-sectional configuration. A preferred weather strip
comprises an elastomer polymer main body member having any of
several shapes conventional in the art.
[0022] The weather strip also comprises an abrasion resistant
decorative layer comprised of an abrasion resistant material
disposed on the outwardly facing surface of the main body member.
As explained in greater detail below, the layer preferably
comprises a moisture crosslinkable olefin polymer and a
thermoplastic vulcanizate.
[0023] With reference to FIG. 1, a cross-section of a preferred
embodiment weather strip for a vehicle in accordance with the
present invention is shown. The preferred embodiment weather strip
is comprised of a main body member 2, made from one or more of a
number of elastomeric polymers known in the art to be suitable for
weather strip applications, and an abrasion resistant decorative
layer 4.
[0024] The elastomeric polymers suitable for use in the main body
member include any conventional material used for such purposes.
Thus, exemplary materials include elastomeric rubbers, as well as
thermoplastic vulcanizates (TPV's) and other elastomeric
polymers.
[0025] Suitable elastomeric rubber compositions for use in the main
body member include, but are not limited to,
ethylene-.alpha.-olefin-non-conju- gated diene rubbers (EODM),
styrene-butadiene rubbers (SBR), acrylonitrile-butadiene rubber,
natural or synthetic isoprene rubber and chloroprene rubber. EODM
rubbers are preferred due to their oxygen, ozone and weather
resistance. Suitable .alpha.-olefins include, but not limited to,
propylene, 1-butene, 1-pentene, 1-hexene, 1-octene and 1-decene. A
preferred .alpha.-olefin is propylene. A preferred group of EODM
compounds suitable for the present invention are
ethylene-propylene-diene terpolymers (EPDM). Suitable
non-conjugated dienes include, but not limited to, 1,4-hexadiene,
dicyclopentadiene and 5-ethylidene-2-norbornen- e. A preferred EODM
for the main body member of the weather strip of the present
invention is ethylene-propylene-ethylidene-norbornene terpolymer or
ethylene-propylene-dicyclopentadiene terpolymer. Various grades of
elastomer thermoset rubber may be used in the invention including
dense elastomers and less dense, sponge elastomers.
[0026] The elastomer of the main body member can further include
various additives known in the art in such concentrations that do
not adversely affect the properties of the compound. Such additives
include, but are not limited to, vulcanization agents, carbon
black, lubricants, plasticizers, fillers, slip agents, processing
oils and antioxidants. These additives are added to the elastomer
prior to formation of the main body member.
[0027] In one preferred embodiment (FIG. 1), the main body member 2
is formed having a hollow tube 6 joined along its longitudinal axis
at a region 8 on its outer circumference to a tangential wall 10.
Attached to one end of the tangential wall is a retention spur 12.
Attached to an opposite end of the tangential wall is a second wall
14. The second wall 14 is substantially perpendicular to the
tangential wall 10 at the junction between them, but gently curls
back toward the tangential wall as the second wall 14 extends from
the tangential wall 10. The second wall 14 terminates at and
defines its distal end 16 as shown in FIG. 1. Approximately midway
between the junction of the tangential wall 10 and the second wall
14, and the distal end 16 of the second wall 14, a third wall 18
substantially parallel to the tangential wall 10 extends from the
second wall 14. Together, the tangential wall 10, the second wall
14 and the third wall 18 define an interior chamber 20. Projecting
from the tangential wall 10 on an opposite side from the hollow
tube 6 are a plurality of sealing lips 22 that extend inward and
upward therefrom toward the interior chamber 20. Attached to a
distal end 24 of the third wall 18 and projecting inward and upward
therefrom toward the interior chamber 20 is a large sealing lip 26.
Depending on the function of the weatherstrip, the make of the
automobile, the shape of the chassis and doorframe, many
alternative embodiments are also contemplated.
[0028] Irrespective of the exact shape of the main body member,
applied to an exteriorly directed surface (not numbered) of the
second wall 14 of the main body member 2 is the abrasion resistant
decorative layer 4 comprised of a crosslinkable olefin polymer and
a thermoplastic vulcanizate. This abrasion resistant decorative
layer 4 is applied along the main body member at those areas that
contact the door, vehicle frame or exterior objects (not pictured)
to improve the wear resistance and aesthetics of the weather strip
at those locations. In addition, the abrasion resistant decorative
layer 4 may be applied to other areas of the main body member 2
that contact these objects for added protection and scuff
resistance, such as the various surfaces of the main body member
(not numbered) that are exposed to and face the interior chamber
20.
[0029] Thermoplastic vulcanizates (TPV's) are polyolefinic
matrices, preferably crystalline, through which thermoset
elastomers are generally uniformly distributed. Examples of
thermoplastic vulcanizates include EPM and EPDM thermoset materials
distributed in a crystalline polypropylene matrix. Any conventional
TPV having the desired weatherability, flexibility and strength may
be used in the present invention. Although not intended to be
limiting, examples of suitable TPVs for use in the present
invention include those prepared by blending an olefinic
thermoplastic and either an ethylene copolymer or terpolymer, such
as disclosed in U.S. Pat. No. 4,990,566 to Hert, or a nitrile
rubber, such as disclosed in U.S. Pat. No. 4,591,615 to Aldred et
al, the disclosure of both of which are incorporated herein by
reference.
[0030] Commercial TPV's are typically based on vulcanized rubbers
in which a phenolic resin, sulfur or peroxide cure system is used
to vulcanize, that is crosslink, a diene (or more generally, a
polyene) copolymer rubber by way of dynamic vulcanization, which is
a process in which the rubber is crosslinked while mixing
(typically vigorously), in a thermoplastic matrix. Although any
cure system is contemplated by the present embodiments, sulfur is
typically preferred over peroxide free radical or a phenolic resin
cure systems because peroxide may degrade and/or crosslink the
polypropylene or polyethylene thermoplastic as well as the rubber.
This is in turn limits the extent of rubber crosslinking that can
occur before the entire mixture degrades or crosslinks and is no
longer thermoplastic, while phenolic cure systems may cause a
yellowish tint to the final product.
[0031] Two examples of preferred commercial TPV's are
SANTOPRENE.RTM. thermoplastic rubber, which is manufactured by
Advanced Elastomer Systems and SARLINK.RTM., available from DSM
Elastomers, both of which are a mixture of crosslinked EPDM
particles in a crystalline polypropylene matrix. These materials
have found utility in many applications which previously used
vulcanized rubber, e.g. hose, gaskets, and the like. TPV's are
noted for their processability as thermoplastics while retaining
the excellent resilience and compression set properties of
vulcanized rubbers.
[0032] A preferred method of preparing a thermoplastic vulcanizate
known by those skilled in the art is to form an admixture of
non-crosslinked elastomeric polymer and polyolefin resin and curing
agent. The admixture is then masticated at a vulcanization
temperature. Preferably the non-crosslinked polymer and polyolefin
are intimately mixed before a curing agent is added. When prepared
in a conventional mixing apparatus such as a multiple-roll mill,
Banbury or Brabender mixer or mixing extruder, this is known as a
"two-pass" cycle. Additional additives may be added, including, but
not limited to those fillers, fire retardants, stabilizers,
pigments and antioxidants described above with respect to the TPO
layer.
[0033] Various fillers and processing materials as well as other
components may be added to the TPV used in the present invention.
Non-limiting examples of such fillers include carbon black, calcium
carbonate, clay, silica, and the like. With respect to processing
materials, various processing oils, waxes and the like intended to
improve the processing of the material may be included in any
concentration that does not significantly detract from the
properties of the TPO.
[0034] The polymer may also be formulated with stabilizers,
pigments and antioxidants to obtain the appropriate weathering
properties. In addition, flame retardant fillers such as aluminum
trihydrate (ATH), magnesium trioxide, calcium carbonate, mica,
talc, or glass may be added. In one embodiment, filler levels can
range from 0 to about 30% by weight.
[0035] A typical TPV is a melt blend or reactor blend of a
polyolefin plastic, typically a propylene polymer, with a
crosslinked olefin copolymer elastomer (OCE), typically an
ethylene-propylene rubber (EPM) or an ethylene-propylene-diene
rubber (EPDM). In those TPV's made from EPDM, the diene monomer
utilized in forming the EPDM terpolymer is preferably a
non-conjugated diene. Illustrative examples of non-conjugated
dienes which may be employed are dicyclopentadiene,
alkyldicyclopentadiene, 1,4-pentadiene, 1,4-hexadiene,
1,5-hexadiene, 1,4-heptadiene, 2-methyl-1,5-hexadiene,
cyclooctadiene, 1,4-octadiene, 1,7-octadiene,
5-ethylidene-2-norbornene, 5-n-propylidene-2-norbornene,
5-(2-methyl-2-butenyl)-2-norbornene and the like.
[0036] As explained in greater detail herein, in the final
composite extrusion, such as incorporated into a door or window
assembly, the at least two polymeric components making up the
abrasion resistant decorative layer are both at least partially
crosslinked (the elastomer rubber in the TPV and the crosslinkable
olefin polymer). Thus, although much of the description herein
refers to the abrasion resistant decorative layer as comprising
crosslinkable polymeric materials (as noted above), it will be
understood that in its preferred final manufactured form, the
composite extrusion of the present invention utilizes an abrasion
resistant decorative layer that comprises at least partially
crosslinked materials.
[0037] The second component of the abrasion resistant decorative
layer 4 is a crosslinkable olefin polymer. This may include
homopolymers, olefin copolymers (copolymers of a polyolefin with
another polyolefin or other polymer), or blends of such polymers.
In a preferred embodiment, the crosslinkable olefin polymer is a
crosslinkable olefinic homopolymer, particularly polyethylene.
Preferred crosslinkable olefinic homopolymers are those that can be
crosslinked by silane grafting. Electron beam radiation
crosslinking is not preferred because of its expense. Likewise,
peroxide crosslinking is not preferred because of the processing
concerns that it entails. However, it is contemplated that the
present invention weather strip and related methods could utilize
such techniques for crosslinking. A preferred crosslinkable olefin
polymer is a silane-grafted polyethylene, and this will be used as
an example in the present discussion.
[0038] Other suitable olefinic homopolymers for use with the TPV in
the abrasion resistant decorative layer include silane grafted
polypropylene, and higher olefin homopolymers. The homopolymers can
be made via a variety of polymerization systems (including
metallocene catalyzed and conventional catalysis systems) and have
a range of molecular weights and other characteristics. In one
preferred embodiment, the homopolymer is a polyethylene having a
M.sub.n of from about 20,000 to 100,000, a M.sub.w of from about
50,000 to 200,000 and a molecular weight distribution of from about
2.5 to 4.0.
[0039] One stage silane crosslinking involves the extrusion of a
direct mixture of the polymer resin with a silane concentrate that
includes a catalyst. The extrudate is subsequently crosslinked in
the presence of water. In two-stage crosslinking, silane is first
grafted to the polymer molecular chains according to known
reactions to yield a silane grafted copolymer. 1
[0040] Subsequently, the silane-grafted copolymer is mixed with a
silanol condensation catalyst and then exposed to water to effect
crosslinking of the copolymer in a two step reaction. First, the
water hydrolyzes the silane to produce a silanol. The silanol then
condenses to form intermolecular, irreversible Si--O--Si crosslink
sites. 2
[0041] The amount of crosslinked silane groups, and thus the final
polymer properties, can be regulated by controlling the production
process, including the amount of catalyst used. A gel test (ASTM
D2765) is used to determine the amount of crosslinking. In one
embodiment and prior to being crosslinked, the polyethylene or
other olefin polymer preferably has a melt flow index determined
according to ASTM D-1238 of about 0.5-20 g/10 min at 190.degree. C.
and 2.16 kg load and a Shore A hardness of about 50-90. Most
preferably, it exhibits a melt flow index of about 0.7-1.2 g/10 min
at 190.degree. C. with a 2.16 kg load, a Shore A hardness of about
70 and a density of about 0.8-1.2 g/cm.sup.3.
[0042] The catalyst can be any of a wide variety of materials that
are known to function as silanol condensation catalysts including
many metal carboxylates and fatty acids. A preferred catalyst is
dibutyltindilaurate.
[0043] In one embodiment, the abrasion resistant decorative layer
preferably includes about 75% to about 87% by weight of the TPV and
from about 9% to about 15% by weight of the crosslinkable olefin
polymer. The abrasion resistant decorative layer can also contain
conventional additives including, but not limited to, organic and
inorganic fillers, plasticizers, slip agents, UV stabilizers,
antioxidants and, as previously mentioned, coloring agents in an
amount up to about 30%, more preferably about 2-5%.
[0044] In one embodiment, a slip agent or other lubricant is added
to the blend prior to processing. Any conventional slip agent
material may be utilized. Preferred slip agents include
polysiloxane slip agents known in the art. The use of such slip
agents reduces the coefficient of friction of the resulting show
layers such that the use of a separate slip coating on the surface
of the finished product is not necessary, resulting in reduced
labor and expense. Such slip agents may generally be present in an
amount of from about 0.1-20.0% by weight, more typically from about
2.0-8.0%.
[0045] In addition, the use of a coloring agent in the blend allows
one to customize the color of the surface of the final weather
strip to match or complement the color of the vehicle or its
interior. The ability of the blend to retain color and gloss is
superior to that of conventional elastomeric rubbers.
[0046] The TPV and the crosslinkable olefin polymer are preferably
pre-blended prior to depositing on the elastomer main body member.
Thus, in one embodiment, the TPV and crosslinkable olefin polymer
may be pre-blended and extruded into pelletized form. Preferably,
the material is dried to eliminate moisture that may start the
crosslinking process of the olefin polymer. The pre-blended mixture
may then be mixed with a crosslinking catalyst in a suitable amount
(for example 2-7% by weight) prior to its extrusion onto the
elastomer main body member.
[0047] Subsequently, the abrasion resistant decorative layer 4 can
be applied to the main body member 2 in one of several different
ways. For ease of description, the different processes will be
described utilizing a two stage crosslinkable, silane-grafted
polyethylene homopolymer blended with a TPV as the abrasion
resistant decorative layer 4 and EPDM as the thermoset elastomer
rubber main body member 2. However, the present invention
contemplates the use of other crosslinkable olefin polymers in the
abrasion resistant decorative layer 4 and other elastomers in the
main body member 2.
[0048] As noted above, the elastomer main body member and abrasion
resistant decorative layer may be extruded, molded, or otherwise
processed in a variety of ways known in the art. Several different
extrusion methods are described below. These are not intended to be
limiting however, and other methods of producing the final
composites are also contemplated, such as, e.g., compression or
injection molding.
[0049] The present invention provides a first preferred technique
for producing a composite extrusion by co-extruding an uncured EPDM
main body member, such as item 2 in FIG. 1, and an uncrosslinked
silane-grafted polyethylene/TPV abrasion resistant decorative
layer, such as item 4 in FIG. 1, through an extrusion die. With
reference to FIG. 5, a schematic diagram is shown outlining the
preferred processing steps in this first preferred technique.
Briefly, an uncured EPDM rubber and crosslinkable polyethylene/TPV
blend are provided 500, 502. The EPDM rubber and the PE/TPV blend
are coextruded 504 to form a main body member and an abrasion
resistant decorative layer, respectively. Subsequently, the
polyethylene in the blend is at least partially crosslinked 506.
The EPDM rubber of the main body member is then at least partially
cured 508 prior to removal of the assembly from the processing line
510.
[0050] With greater detail and with further reference to FIG. 2, a
first extruder 50 for processing a blend of a silane-grafted
crosslinkable polyethylene and a TPV, a second extruder 52 for
processing a sponge EPDM and a third extruder 54 for processing a
dense EPDM are placed in communication with an extrusion die 56.
The term "sponge EPDM" refers to an EPDM that contains blowing
agents. The term "dense EPDM" refers to an EPDM that does not
contain any blowing agents. For ease of description, the production
process will be described using the dense extruder 54, although in
actual practice both are typically used concurrently, depending on
the application. In order to ensure sufficient flow of the EPDM
compound for subsequent extrusion, the EPDM extruder 54 is
preferably maintained at a temperature of from about 70.degree. C.
to about 85.degree. C. For the same reason, the PE/TPV extruder 50
is preferably maintained at about 130.degree. C. to about
210.degree. C. The extrusion die 56 is preferably maintained at
about 110.degree. C. on an EPDM side 58 and from about 200.degree.
C. to about 260.degree. C. on an PE/TPV side 60. Insulation (not
shown) between the two sides of the extrusion die allows for this
disparity in temperatures to be more easily achieved. For a dense
EPDM, the EPDM is extruded at a pressure of from about 2000 to
about 5000 psi, and most preferably about 4000 psi. For a sponge
EPDM, the EPDM is extruded at a pressure of about 1000 psi to about
3000 psi, most preferably about 2500 psi. The PE/TPV and EPDM are
co-extruded such that the PE/TPV layer mechanically bonds with the
EPDM through molecular chain inter-diffusion and entanglement. The
thickness of the resulting PE/TPV layer is preferably from about
0.1 to about 1.5 mm, and typically about 0.5 mm.
[0051] Referring further to FIG. 2, the composite extrusion (not
shown) comprising the extruded EPDM and PE/TPV is then passed
through a steam bath 62 to effect crosslinking of the polyethylene
in the PE/TPV layer. The steam bath 62 is preferably maintained at
a temperature of from about 100.degree. C. to about 110.degree. C.
To cure the EPDM, the composite extrusion is then passed through an
oven 64 or other curing device at a temperature of from about
180.degree. C. to about 270.degree. C., depending on the grade of
EPDM used in the main body member 2. In a particularly preferred
embodiment, the composite extrusion is passed through a number of
temperature zones in the oven 64 starting at about 200.degree. C.
for about 15 to about 50 seconds, ramping up to about 220.degree.
C. for about 45 seconds to about 2.4 minutes, and then ramping down
to about 210.degree. C. for about 15 to about 50 seconds, prior to
exiting the oven 64. Preferably, the total oven cure time is
between about 1 minute and about 4 minutes. The composite extrusion
is then cooled in a water or air cooling tank 66 at about
30.degree. C. to 90.degree. C., and most preferably about
60.degree. C., before removing the composite extrusion from the
manufacturing line.
[0052] In a second preferred technique in accordance with the
present invention, the uncured PE/TPV is extruded onto the main
body member after the EPDM has been at least partially cured. With
reference to FIG. 6, a schematic diagram is shown outlining the
processing steps in this third preferred technique. Briefly, an
EPDM rubber and crosslinkable PE/TPV are provided 600, 602. The
EPDM rubber is extruded 604 into a main body member and the main
body member is subsequently at least partially cured 606. The
PE/TPV is extruded 608 as an abrasion resistant decorative layer
onto the main body member. The PE of the PE/TPV abrasion resistant
layer is crosslinked 610 prior to removal 612 of the assembly from
the processing line.
[0053] With additional detail and with further reference to FIG. 3,
an extruder 52 for sponge EPDM and an extruder 54 for dense EPDM
are placed in communication with a first extrusion die 70. For ease
of description, the production process will be described using only
the dense extruder 54, although in actual practice both are
typically used concurrently to make different sections of the same
part. EPDM is extruded from the rubber extruder 54 through the
first die 70 to form a main body member (not shown). The main body
member is then passed through an oven 64 to cure the EPDM. Upon
emerging from the oven 64, an abrasion resistant layer (not shown)
comprising the above described PE/TPV is extruded from a second die
72 that is fed by a plastic extruder 50 onto the cured main body
member to form a composite extrusion. The residual heat of the EPDM
main body member mechanically bonds the PE/TPV therewith through
diffusion. An embossing wheel 74 assists in bonding the EPDM to the
PE/TPV by pressing the two layers together. In addition, the
embossing wheel 74 may be used to print surface patterns on the
composite extrusion (such as a "leather-like" texture). The
composite extrusion is passed through a water cooling bath 62 to
cool the composite and to crosslink the polyethylene of the PE/TPV
prior to removal 76 from the manufacturing line. The temperatures
and pressures for the second technique are preferably similar to
those used for the first technique in all respects except that the
first die 70 is at a temperature from about 100.degree. C. to about
120.degree. C., and the second die 72 is at a temperature from
about 200.degree. C. to about 220.degree. C. In addition, although
not typically independently heated, the embossing wheel 74 may be
at a temperature from about 170.degree. C. to about 210.degree. C.,
and typically about 195.degree. C., due to the residual heat from
the extrudate and the adjacent extruder(s).
[0054] In a third technique, an uncured PE and TPV blend is
extruded into a sheet and then laminated onto a cured EPDM main
body member. With reference to FIG. 7, a schematic diagram is shown
outlining the processing steps in this third preferred technique.
Briefly, a thermoset elastomer rubber and the above described
PE/TPV are provided 700, 702. The EPDM rubber is extruded 704 into
a main body member and the PE/TPV is extruded 706 into an abrasion
resistant decorative sheet layer. The main body member is at least
partially cured 708 and the sheet layer then laminated 710 onto the
main body member. The PE of the sheet layer is then at least
partially crosslinked 712 before the resultant assembly is cooled
and removed 714 from the processing line.
[0055] With additional detail and with further reference to FIG. 4,
an extruder 52 for sponge EPDM and an extruder 54 for dense EPDM
are placed in communication with a first extrusion die 70. As
stated earlier, for ease of description, the production process
will be described using the dense extruder 54, although in actual
practice both are typically used concurrently. EPDM from the rubber
extruder 54 is extruded through the first die 70 into a main body
member (not shown). The main body member is passed through an oven
64 to cure it. PE/TPV is extruded from a second extruder 50 through
a second die 82 to form an abrasion resistant layer in the form of
a sheet 80. An embossing wheel 74 then bonds the uncured PE/TPV
sheet 80 to the main body member to form a composite extrusion (not
shown). The composite extrusion is then passed through a water bath
62 to crosslink the polyethylene component of the PE/TPV blend and
to cool the composite prior to removal from the line 76. The
temperatures and pressures for the third technique are preferably
similar to those used for the first technique in all respects
except that the first die 70 temperature is from about 100.degree.
C. to about 120.degree. C., the second die 82 temperature is from
about 200.degree. C. to about 220.degree. C. and the lamination
wheel is at a temperature from about 170.degree. C. to about
210.degree. C., and preferably about 185.degree. C.
[0056] While various changes and adaptations may be made to the
above methods without departing from the scope of the invention,
with regard to the first preferred technique described, it is
preferable that the polyethylene of the PE/TPV blend is crosslinked
prior to passing the composite extrusion through the oven.
EXAMPLES
[0057] The following examples are provided to better illustrate
certain preferred embodiments. They should in no way be considered
limiting of the scope of the invention. Various samples were
prepared according to the above embodiments. The formulation of the
abrasion resistant decorative layer for these samples are listed in
table 1.
1 TABLE 1 Parts Material Sample 1 Sample 2 Santoprene
8211-35.sup.(1) 0.805 0.775 Syncure S1054.sup.(2) 0.126 0.106
MarkScreen 1413.sup.(3) 0.0051 0.0051 Colorant 0.03 0.05 Siloxane
additive 0.0 0.05 Crosslink accelerator 0.0339 0.0339 Total 1.000
1.000 .sup.(1)An EPDM/PP TPV available from Advanced Elastomer
Systems .sup.(2)A moisture crosslinkable silane grafted
polyethylene available from PolyOne Corp., Cleveland .sup.(3)A UV
stabilizer available from Crompton Corp., Hahnville, La.
[0058] The materials were blended in a Werner Pfleiderer 25 mm twin
screw at 145.degree. C. and processed in pelletized form. The
material was then extruded as a one inch wide continuous strip
through an extrusion die at 204.degree. C. (400.degree. F.). The
properties of the material of sample 1 were as follows.
2 TABLE 2 Hardness (Shore A) 66 Tensile at break (MPa) 5.9
Elongation at break (%) 385 100% modulus (MPa) 2.4 Compression set
28 Tear Strength (kN/m) 34 Low temp brittleness (.degree. C.) -50
Specific gravity 0.91 Ash (%) 0 Fogging 88 Oil swell (%) 18.4 72
hrs at 90.degree. C. No tackiness, no oil migration
[0059] In addition, the coefficient of friction of the present
decorative layer is much lower than prior coatings used in such
applications. As such, while prior automobile composites required a
spray on slip-coating added to the finished part to reduce the
coefficient of friction ("COF") to the desired range, the present
decorative layers can achieve acceptable COF values without the
addition of a separate slip-coating by the addition of siloxane to
the formulation. To demonstrate, six formulations (formulations
A-F) were prepared. A and B were conventional formulations
containing a thermoplastic elastomer conventionally used as show
layers for automobile weather strips with the addition of a
colorant. They differ only in the fact that a spray on slip coating
was added to B. Formulations C-E are embodiments of the present
invention containing varying amounts of siloxane. The formulations
of each sample are set forth below.
3TABLE 3 Formulations A + B Component Weight % Uncured styrenic
block copolymer 96.00 TPE (Kraton G7431) Colorant 4.00
[0060] A spray on slip coat was added to the finished part of
formulation B. The composition of the present embodiments is set
forth in Table 4 with values in wt. %.
4 TABLE 4 Component C D E F Sarlink X6145 77.96 74.37 68.22 71.20
Syncure 12.23 11.67 12.06 11.17 S1054A.sup.1 Syncure 3.38 3.23 3.33
3.09 S1006B.sup.2 Colorant 3.28 6.27 3.24 6.00 UV Stabilizer 0.80
0.78 Siloxane 2.35 4.46 12.37 8.54 TOTAL 100.00 100.00 100.00
100.00 .sup.1A moisture curable polyethylene available from PolyOne
Corp. .sup.2A catalyst masterbatch for the moisture curable PE
[0061] Both the static and dynamic COF values were measured for all
the finished parts according to ASTM D1894. The results are set
forth in Table 5.
5TABLE 5 FORMULATION Static Dynamic A 2.949 3.491 B 0.322 0.317 C
1.245 1.973 D 1.285 2.06 E 1.534 2.016 F 1.427 1.834
[0062] As can be seen, the uncoated parts made according to the
present formulations have a much lower COF than the uncoated prior
art parts. Therefore, through the use of a siloxane additive to the
composition of the show layer, static COF values down to about 1.2
or lower and typically between 1.2 and 1.6 may be obtained.
Similarly, dynamic COF values of such layers may range down to
about 1.9 or lower with typical values ranging from about 1.9 to
2.1. Although typically not as low as slip coated parts, the COF
values obtainable for the present embodiments are acceptable for
use in typical automobile applications without the need for an
additional slip coat.
[0063] The invention has been described with reference to various
preferred embodiments. Obviously, modifications and alterations
will occur to others upon a reading and understanding of the
specification. The invention is intended to include all such
modifications and alterations insofar as they come within the scope
of the appended claims and the equivalents thereof. Thus, for
example, composite extrusions for other parts (such as automobile
glass run channels) in addition to vehicle weather strips can be
manufactured by the techniques of the present invention.
* * * * *