Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
1998-10-19
2001-02-13
Niland, Patrick D. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S086000, C524S094000, C524S098000, C524S099000, C524S589000
Reexamination Certificate
active
06187859
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates generally to the production of thermoplastic polyurethane elastomers and, more specifically, to the production of an improved light stable polyether/polyol aliphatic urethane elastomer.
BACKGROUND OF THE INVENTION
The use of low unsaturation level polyols made from double metal cyanide catalysts in combination with chain extenders in the preparation of thermoplastic elastomers is disclosed in U.S. Pat. Nos. 5,096,993 and 5,185,420 both to Smith et al., incorporated herein by reference. Prior to the use of double metal cyanide catalysts for the preparation of high molecular weight polyols, the thermoplastic polyurethane elastomers produced had poor physical properties such as being too hard due to high levels of terminal unsaturation in the polyols used in their production.
The thermoplastic polyurethane elastomers of the '993 and '420 patents to Smith et al. describe the preparation of thermoplastic elastomers made with polyols have less than 0.04 meq/g of end group unsaturation, particularly, thermoplastic elastomers characterized by enhanced softness.
Because of their softness, thermoplastic elastomers are frequently used in the construction of automotive interior trim components. Automotive manufacturers frequently specify that the elastomers used to produce interior trim components have adequate long-term stability and resistance to degradation by ultra violet light and that the elastomers must also meet specific manufacturing specifications for resistance to ultra violet light exposure.
Commonly, in order to achieve the manufacturing specifications for resistance to ultra violet exposure, antioxidants, ultra violet light stabilizing agent(s), and pigment(s) are added to elastomers.
However, to date, soft thermoplastic polyurethane elastomers have not been produced which are able to meet or exceed manufacturers requirements for withstanding prolonged levels of artificial weathering which simulates exposure to the heat and ultra violet radiation and sunlight. Additionally, due to the previous presence of end group unsaturation of polyols with molecular weights greater than 2,000, soft (low durometer) aliphatic thermoplastic urethane elastomers were not available in a dry castable powder or spheroidal particle forms.
SUMMARY OF THE INVENTION AND ADVANTAGES
The present invention provides a light stable polyether/polyol based aliphatic thermoplastic urethane elastomer and is comprised of the reaction product of a polyol, chain extender, organic diisocyanate, ultra violet stabilizing agent, an antioxidant, pigment, and a urethane catalyst.
More particularly, the present invention provides a light stable polyether/polyol based aliphatic urethane thermoplastic elastomer wherein the ultra violet stabilizing agents include hindered amine light stabilizers (HALS) and a hydroxyphenyl benzotriazole are present in a ratio in a range of 1:1 to 2:1 at a total concentration in a range of 0.1% to 2.0%, the antioxidant being present at a total concentration in a range of 0.1% to 1.0% and the pigment being present at a total concentration in a range 1.0% to 2.0%, whereby the elastomer produced thereby can withstand Xenon arc artificial weathering with a DE≦53.00 after 2450 kilojoules of exposure.
The present invention also provides a method for preparing light stable automotive components from a polyether/polyol based aliphatic urethane thermoplastic elastomer, and a method for preparing the subject thermoplastic elastomer into a castable powder.
DETAILED DESCRIPTION IN THE INVENTION
The present invention provides an improved light stable polyether/polyol based aliphatic urethane thermoplastic elastomer in that it can withstand Xenon arc artificial weathering with a DE≦3.00 after 2450 kilojoules of exposure. Furthermore, the light stable elastomer of the present invention is prepared using critical ratios of ultra violet stabilizing agent, antioxidant, and pigment. This advance in the art comes at a time which is particularly timely given the current trend towards the increased use of thermoplastic elastomers for automotive interior trim components and at a time where automotive manufacturer s are demanding components which can last longer and remain light and heat stable over time.
Certain aspects of the p resent invention are conventional, employing reactants known in the art as will be seen from the disclosure set forth below. The unique and critical combination of ultra violet stabilizing agents, antioxidant and pigment employed in the present invention results in an improved light stable urethane thermoplastic elastomer.
The prior art, in particular, as represented by U.S. Pat. Nos. 5,096,993 and 5,185,420 to Smith et al. teach how to achieve a soft, thermally stable elastomer utilizing low unsaturation level polyols prepared by double metal cyanide complex catalysis. These references teach the use of certain compounding ingredients such as antioxidants, plasticizers, ultra violet stabilizers, adhesion promoters, fillers, and pigments employed in an amount between zero and about 75% based upon the total weight of the composition. These references are silent as to any criticality involving the ratios of ultra violet stabilizing agents, antioxidants, and pigment and the effect these critical ratios and amounts have on the ability of the elastomers to withstand artificial weathering, i.e., Xenon arc exposure.
The present invention uses conventional urethane chemistry along with critical amounts of ultra violet stabilizers, antioxidant(s), and pigment(s) to give the desired light stability and weathering properties demanded by automobile manufacturers.
The thermoplastic elastomers of the present invention may be made by a “one-shot” reaction process. The “one-shot” technique involves mixing, in a suitable container, polyol, chain extender, organic diisocyanate, ultra violet stabilizing agent(s), antioxidant, pigment(s), and urethane catalyst and, then, agitating the mixture for approximately 20 to 30 seconds. These elastomers can also be made by preblending a portion of the polyol, the antioxidant, catalyst and UV/heat stabilizers. The blend is added to an agitated, heated tank of a urethane casting machine; isocyanate is placed into a separate agitated, heated tank; chain extender/crosslinker is placed into a third tank; and pigment masterbatch with the additional polyol is added at the mixhead. The components are metered individually using gear pumps or other pumps with the required metering accuracy, with suitable flow control devices, to a low pressure mixhead for blending. This mixture may be cast onto a temperature and speed controlled belt for completion of the reaction. Various temperatures could be maintained in different areas of the chamber.
The mixture from the mixing head of the urethane casting machine could also be used as the feed for a twin screw extruder. Various screw sections could be set up to convey the liquid to continue polymerization, melt and blend the elastomer, and the final unpigmented elastomer could be fed to a strand die for pelletizing. The extruder output could also be used to make spheroidal beads of the desired size for dry casting.
The extrusion operation could also be used to melt blend dry pigment for coloring/pigmenting the elastomer. The dry blended pigment would be fed into the extruder using a side feeder which would meter the proper amount into a clear melt mixture. The output of the side feeder would be synchronized with the output of the extruder.
Finally, loss in weight belt feeders could be used to replace the metering machine and the ingredients would be fed directly into the throat of the twin screw extruder which would perform the blending, polymerization, melting, and pigmentation operations.
In preparing the improved light stable polyether/polyol based aliphatic urethane thermoplastic elastomer of the present invention, the polyether/polyol, diisocyanate, chain extender, and other components are typically reacted under conditions of elevated temperature. A pre
Gerard Victor E.
Humphrey William M.
Davidson Textron Inc.
Hayes, Soloway, Hennessey Grossman & Hage, P.C.
Niland Patrick D.
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