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
1998-03-03
2001-05-29
Mullis, Jeffrey C. (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...
C525S206000, C525S227000, C525S233000, C525S238000, C525S241000
Reexamination Certificate
active
06239221
ABSTRACT:
BACKGROUND OF THE INVENTION
Grafted rubber compositions are well known in the art. Poly(acrylonitrile butadiene styrene) or ABS is widely known and used as a molding and extrusion composition. In ABS, polybutadiene is grafted with acrylonitrile and styrene. For outdoor applications where the polymer composition is exposed to sunlight and weather, a saturated rubber such as polybutyl acrylate (PBA) polyethylene propylene (EP) or polyethylene propylene diene monomer (EPDM) is used in place of the butadiene used in ABS. Blends of these grafted saturated rubbers are also known.
1. Field of the Invention
The present invention is directed to a polymer composition which is a blend of (a) an olefin rubber such as ethylene propylene diene monomer rubber grafted with styrene and acrylonitrile (EPDM-g-SAN); (b) an ungrafted olefin rubber such as ethylene propylene diene monomer rubber (EPDM); (c) a poly(acrylonitrile styrene) matrix; and (d) optionally a butyl acrylate rubber grafted with styrene and acrylonitrile. These polymer compositions have a desirable balance of low gloss and impact strength which makes them especially suitable as molding and extrusion compounds for certain outdoor applications.
2. Description of Related Art
Butyl acrylate rubber and EPDM rubbers grafted with styrene and acrylonitrile are well known in the art. Such compositions are taught in U.S. Pat. No. 3,489,822 (Witt et al); U.S. Pat. No. 4,127,617 (Arrighetti et al); U.S. Pat. No. 4,145,378 (Arrighetti et al); and U.S. Pat. No. 4,912,162 (Kishida et al). Blends of a butyl acrylate rubber grafted with styrene and acrylonitrile (BA-g-SAN) and an EP or EPDM rubber grafted with styrene and acrylonitrile (EP-g-SAN or EPDM-g-SAN) are also well known and are taught in U.S. Pat. No. 4,877,826 (Beyer); U.S. Pat. No. 4,946,894 (Henton et al) and U.S. Pat. No. 5,112,895 (C. J. Chen and F. M. Peng).
SUMMARY OF THE INVENTION
The present invention is directed to molding and extrusion compositions which have low sheet gloss (less than 50 preferably less than 40 at a 60° angle) and good Izod impact (greater than 50 J/m). The compositions comprise (a) an olefin rubber grafted with a vinyl aromatic monomer and an unsaturated nitrile monomer and optionally one or more compatible comonomers; (b) an ungrafted olefin rubber; (c) an SAN matrix polymer; and (d) optionally an acrylate rubber grafted with vinyl aromatic monomer and an unsaturated nitrile monomer and optionally one or more compatible comonomers;
The EP and EPDM rubbers used in the present invention are well known in the art. Their description and a means for the preparation thereof have been disclosed in U.S. Pat. No. 3,489,821 and U.S. Pat. No. 4,202,948, both of which teachings are incorporated herein by reference. While a variety of alpha mono-olefins may be used in preparing EPDM rubbers, most desirably are those elastomers comprising a terpolymer of ethylene and propylene with an ethylenically unsaturated copolymerizable non-conjugated diene monomer. Illustrative non-limiting examples of suitable diene which may be used include dicyclopentadiene, ethylidene norbornene and 1,4-hexadiene.
Methods of preparing EPDM graft copolymers are also well known in the art. The graft copolymer is polymerized in the presence of the rubbery EPDM polymer utilizing either emulsion, suspension or solution polymerization techniques. Examples of EPDM graft copolymers are taught in U.S. Pat. Nos. 3,489,821, 3,489,822, 3,642,950 and 4,314,041 all of which are incorporated herein by reference. Preferred grafted EPDM rubbers have a weight average particle size from 0.1 &mgr; to 1.0 &mgr;. Most preferred are those rubbers prepared by grafting the rubber spine in a solution or suspension process having a particle size of from 0.3 &mgr; to 0.6 &mgr;.
Acrylate rubbers for use in the present invention are well known in the art and described, for example, in U.S. Pat. Nos. 3,830,878; 4,341,883; 3,944,631; 3691,260 and 4,224,419, the teachings of which are incorporated herein by reference. Preferred acrylate rubbers are crosslinked homopolymers of C
1-8
alkyl acrylates, especially butyl acrylate or 2-ethylhexyl acrylate, and crosslinked copolymers thereof with up to about 25 weight percent, preferably up to about 10 percent, of a copolymerizable comonomer. Suitable copolymerizable comonomers include monovinylidene aromatic monomers, e.g. styrene, alpha-methyl styrene, etc., acrylonitrile and alkyl methylacrylates such as methyl methacrylate. A preferred acrylate rubber comprises butyl acrylate optionally containing various di-and tri-vinyl substituted crosslinking and graft enhancing agents present in an amount up to about 5 percent by weight based on total rubber weight.
Preferably the acrylate rubber is prepared by an emulsion process. Emulsion polymerized acrylate rubbers may be partially agglomerated as is known in the art in order to provide a greater variety of particle size distribution in the resulting acrylate rubber product thereby controlling gloss and impact properties of the polymer. The rubber particles can also be grown to various sizes by varying the polymerization conditions and/or a mixture of previously prepared large and small seed particles may be employed to form the grafted rubber. The grafted acrylate rubber's weight average particle diameter is preferably from about 0.05 &mgr; to about 0.5 &mgr;, most preferably from 0.1 &mgr; to 0.25 &mgr;. Particle diameters are measured in the latex form of the rubber before grafting using techniques of transmission Electron Microscopy or hydrodynamic chromatography as disclosed in U.S. Pat. No. 4,419,496. Grafting of acrylate rubbers is also well known in the art and is disclosed, for example, in the above cited U.S. Pat. Nos. 3,830,878; 4,341,893; 3,944,631; 3,691,260 and 4,224,419. Preferably the crosslinked acrylate rubber is grafted by means of an emulsion process.
The amount of grafting in both the EPDM and acrylate rubbers may vary over a wide range. As defined by percent grafting (attached rigid phase weight/rubber weight×100) the percent graft may be from about 5 to about 150. Preferred percent grafting limits are from about 10 to 100. Desirable grafting levels are dependent on particle sizes. Large rubber particles generally possess lesser amounts of graft copolymer on a percentage basis. While it is preferred that each rubber substrate be grafted with a graft copolymer which is similar to the matrix resin, different copolymers may be employed for the various graft copolymers and matrix copolymer provided that these different copolymers are mutually compatible.
The matrix copolymer is typically prepared during the polymerization processes used to graft the EPDM and acrylate elastomers. Preferred are matrix copolymers comprising from 60 to 90% vinyl aromatic monomer, 10 to 40% nitrile monomer and 0 to 20 percent by weight of an acrylate, e.g. methylmethacrylate. More preferred matrix copolymers comprise 65 to 80% by weight styrene, 20 to 35% by weight acrylonitrile and 0 to 20% by weight of methylmethacrylate.
In addition to the matrix polymer formed during the grafting process, additional separately prepared compatible matrix polymer may be added to the compositions of this invention. Separately prepared matrix may be the same or different from the above described matrix formed during the grafting step.
The total amount of rubber in the blends is in the range of from 5 to 30% by weight based on the total weight of components (a), (b), (c) and (d). Preferably, when component (d) is not included, the total amount of rubber in the blend is in the range of from about 20 to about 30% by weight based on the total weight of components (a), (b) and (c). When all four components are present, the preferred amount of rubber is in the range of from about 10 to about 30% by weight.
By means of an appropriate selection of the rubber particle size, amount of crosslinking and the total amount of EPDM and acrylate rubber used in the polyblend, compositions having a wide variety of product properties may be prepared.
Stabilizers
Bayer Antwerpen S.A./N.V.
Gil Joseph C.
Mullis Jeffrey C.
Preis Aron
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