Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2002-01-25
2003-05-27
Seidleck, James J. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S201000, C525S221000, C525S072000, C525S078000, C525S360000, C525S361000
Reexamination Certificate
active
06569947
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a maleic anhydride modified ethylene polymer/ionomer/high density polyethylene blend having improved impact resistance. More specifically but not by way of limitation, the present invention relates to the incorporation of a maleic anhydride modified ethylene polymer (e.g., maleic anhydride grafted high density polyethylene, MAN-g-HDPE; maleic anhydride grafted very low density polyethylene, MAN-g-VLDPE; maleic anhydride grafted ethylene propylene rubber, MAN-g-EPR; or maleic anhydride grafted ethylene propylene diene monomer rubber, MAN-g-EPDM), into an ionomer/high density polyethylene blend in order to improve low temperature Izod impact.
2. Description of the Related Art
It is generally known in the art to employ a thermoplastic alloy based on a blend of ionomer and high density polyethylene or polyamide for injection molding exterior automotive molded-in-color fascia, bumper covers, side moldings and other decorative trim. These types of polymer blends are disclosed, for example, in U.S. Pat. Nos. 4,387,188 and 5,866,658, respectively. Each involve a copolymer of an &agr;-olefin, typically ethylene, copolymerized with an &agr;, &bgr;-ethenically unsaturated carboxylic acid, typically acrylic acid, methacrylic acid or mixtures thereof, wherein the acid copolymer has preferably from 5 to 80 percent of the acid groups neutralized with metal ions such as zinc, sodium or the like. Such ionomers are commercially available under the tradename Surlyn® from E. I. du Pont de Nemours and Company. In the '188 patent, the partially neutralized acid copolymer is blended with a linear polymer of &agr;-olefins and glass fiber to produce a molding resin. In the '658 patent, the highly neutralized acid copolymer is blended with one or more polyamides which constitute a continuous or co-continuous phase of the resulting blend. One difficulty with such blends is the achieving and sustaining of low temperature impact resistance, particularly in the absence of reinforcing fiber.
BRIEF SUMMARY OF THE INVENTION
In view of the above-mentioned problem, it has now been discovered that the addition or incorporation of maleic anhydride modified ethylene derived polymer (e.g., a maleic anhydride grafted high density polyethylene, MAN-g-HDPE; maleic anhydride grafted very low density polyethylene, MAN-g-VLDPE; maleic anhydride grafted ethylene propylene rubber, MAN-g-EPR; or maleic anhydride grafted ethylene propylene diene monomer rubber, MAN-g-EPDM) into an ionomer/high density polyethylene blend improves low temperature Izod impact. More specifically, the low temperature Izod impact for non-fiber reinforced blends of ionomer/HDPE is essentially doubled by the addition of MAN-g-HDPE.
Thus the present invention provides a maleic anhydride modified ethylene polymer/ionomer/high density polyethylene blend having improved impact resistance comprising for every one hundred parts by weight of ionomer/high density polyethylene blend from one to twenty parts by weight ethylene polymer modified with from 0.2 to 5.0 weight percent maleic anhydride. Preferably the ethylene polymer modified with maleic anhydride is selected from the group consisting of a maleic anhydride grafted high density polyethylene (MAN-g-HDPE), a maleic anhydride grafted very low density polyethylene (MAN-g-VLDPE), a maleic anhydride grafted ethylene propylene rubber (MAN-g-EPR), a maleic anhydride grafted ethylene propylene diene monomer rubber (MAN-g-EPDM), and mixtures thereof.
The present invention further provides a method of improving impact resistance of an ionomer/high density polyethylene blend to comprising the steps of:
(i) adding for every one hundred parts by weight cumulative of ionomer and high density polyethylene from one to twenty parts by weight maleic anhydride modified ethylene polymer; and
(ii) mixing the maleic anhydride modified ethylene polymer, ionomer and high density polyethylene at elevated temperature and high shear rate.
Most preferably the polyethylene modified with maleic anhydride is a maleic anhydride grafted high density polyethylene (MAN-g-HDPE).
DETAILED DESCRIPTION OF THE INVENTION
The present invention involves the addition of maleic anhydride modified ethylene polymer to an ionomer/high density polyethylene blend in order to sustain or improve impact resistance of the resulting blend. For purposes of describing this invention the term “copolymer”, unless otherwise specified, refers to a polymer derived from the polymerization of two or more different monomers that are alternative reactants during the polymerization. As such, the term copolymer is intended to include both “terpolymer” as well as polymers produced from more than three comonomers yet also includes “bipolymer”. The term “blend” is intended to refer to a combination, admixture and/or plurality of polymers with or without additives that collectively function or result in a thermoplastic matrix or polymer alloy, albeit, micro-analysis may reveal dispersed, continuous, and/or discontinuous phases. Also, the phrase “consisting of” means that the recited components are essential, while smaller amounts of other components may be present to the extent that they do not detract from the operability of the present invention. In contrast, the term “comprising” is intended to acknowledge that significant amount of other components may be present provide that some of the benefit and/or advantages of the instant invention are still being realized (e.g., improved or sustained impact characteristics, and the like).
The ionomer/high density polyethylene blends useful according to the instant invention broadly includes any such thermoplastic alloy based on combining or mixing a neutralized or partially neutralized ethylene/&agr;,&bgr;-unsaturated carboxylic acid copolymer (referred to herein as acid copolymer) with a thermoplastic linear polyethylene. Such blends may and frequently are reinforced with various fibers. These types of polymer blends with reinforcing fibers are disclosed, for example, in U.S. Pat. No. 4,387,188, incorporated herein by reference. As taught in this reference, the acid copolymer content of the blend was typically from 38 to 90 weight percent of the blend; however, it is now contemplated that 20 to 80 weight percent acid copolymer is a more preferred range. Such acid copolymers from which the ionomer is derived are further described in U. S. Pat. Nos. 3,520,861; 4,026,967; 4,252,924; and 4,248,990, incorporated herein by reference. The neutralized and partially neutralized ionic copolymers (ionomers) are described in U.S. Pat. No. 3,264,272, also incorporated herein by reference.
The high density polyethylene of the ionomer/HDPE blend according to the present invention can be any such thermoplastic linear polyolefin as generally known in the art. The density of the polyethylene will range from about 0.91 to 0.97, preferably 0.935 to about 0.970, and most preferably 0.95 to about 0.97. The HDPE will typically be characterized by a melt index generally within the broad range of 0.1 to 100, but preferably is from about 0.3 to about 10, most preferably from about 2 to about 6 for injection molded grade and less than 2 for film and blow molding grades. As such, the HDPE will be a relatively high molecular weight polymer of predominantly ethylene; with or without small amounts of other copolymerized &agr;-olefins resulting in a linearity typically characterized by about eight or less branch points per thousand carbon atoms as generally known in the art. The HDPE content of the blend is typically from 20 to 80 weight percent of the blend, preferably from 50 to 75 percent and most preferably from 60 to 70 weight percent.
The maleic anhydride modified ethylene polymer impact additive will preferably have from 0.2 to 5.0 weight percent maleic anhydride comonomer or an equivalent acid content incorporated into the ethylene polymer. For purposes of the present invention, it is contemplated that other unsaturated dicarboxylic acid such as fumaric
Asinovsky Olga
E. I. du Pont de Nemours and Company
Seidleck James J.
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