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
1999-10-19
2002-11-05
Buttner, David J. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S309000, C525S902000
Reexamination Certificate
active
06476126
ABSTRACT:
SUMMARY OF THE INVENTION
A thermoplastic molding composition useful in the preparation of molded articles is disclosed. The composition contains a blend of
(A) a grafted rubber comprising a crosslinked rubber substrate which contains
(A1) a vinylaromatic polymer core and
(A2) an acrylate rubber shell, to which substrate is grafted
(A3) a grafted phase,
(B) a copolymeric matrix, and
(C) (co)polycarbonate resin.
Preferably containing no additional grafted rubber components, the composition is suitable for preparing articles having low haze, high gloss and which are free of corona defect.
BACKGROUND OF THE INVENTION
It has long been known that styrene/acrylonitrile copolymers (SAN) may be imparted improved impact properties by the incorporation of rubbers. In ABS polymers, diene polymers are used as the rubbers for toughening, most notably at low temperatures; however, the relatively poor weathering and aging resistance make these materials less favored in more demanding applications. In some such applications, use has successfully been made of crosslinked acrylic acid ester polymers; these are the well-known ASA copolymers. Such have been described in U.S. Pat. No. 3,055,859 and in German Patents 1,260,135 and 1,911,882 Accordingly, the preferably crosslinked, rubbery acrylic acid ester polymer which serves as the grafting base (substrate) may be prepared by emulsion polymerization and the latex thus prepared may then be grafted, preferably by emulsion, with a mixture of styrene and acrylonitrile. The art thus has long recognized that improved impact strength, notched Izod and greater hardness are associated with such ASA products which have as a grafting base a coarse polyacrylate latex.
The art refers to “hard” and “soft” segments in terms of the relative position of their glass transition temperature vis a vis room temperature. “Hard” means T
g
above room temperature and “soft” means below room temperature, as well as to core/shell structures including structures which contain a multiplicity of shells. Multi-phase structured emulsion copolymers, including hard-soft and hard morphologies have been disclosed in EP 534,212 and in the documents referenced therein. Accordingly, graft copolymers with a hard core of polystyrene, a first butyl acrylate shell and an outer SAN shell have been disclosed in the art.
The relevant art also includes U.S. Pat. No. 4,148,842 which disclosed an impact resistant blend containing polycarbonate resin and an interpolymer modifier comprising a crosslinked (meth)acrylate, crosslinked SAN and uncrosslinked SAN components. Compositions containing polycarbonate and ASA graft polymer and the methods for their preparation were disclosed in U.S. Pat. No. 3,655,824 and in U.S. Pat. No. 3,891,719. Compositions containing polycarbonate, ASA and PMMA were disclosed in U.S. Pat. No. 4,579,909. JP 50154349 disclosed flame retardant compositions containing PC and ASA.
DETAILED DESCRIPTION OF THE INVENTION
The inventive thermoplastic composition is suitable for the preparation of molded articles having low haze, high gloss characterized in the absence of corona surface defects. The composition comprises a blend of 10 to 50 percent by weight (wt. %), preferably 20 to 40 wt. % of grafted rubber (A), 0 to 40, preferably 10 to 30, wt. % of a copolymeric matrix (B), and 10 to 90, preferably 30 to 70, wt. % of (co)polycarbonate resin (C). More specifically, (A) denotes a grafted rubber comprising 30 to 80 percent, preferably 40 to 70 percent, relative to its weight, of a crosslinked rubber substrate which contains
(A1) about 1 to 50%, relative to the weight of the substrate, of a core which contains at least one vinylaromatic polymer, and
(A2) about 50 to 99%, relative to the weight of the substrate of a shell containing at least one polymerized acrylate, to which rubber substrate is grafted
(A3) 70 to 20 percent, preferably 60 to 30 percent, relative to the weight of the grafted rubber, of a grafted phase. The inventive composition may include poly(alkyl)methacrylate, preferably poly(methyl)methacrylate, (PMMA) as an additional component, (D).
The composition, which in a preferred embodiment contains no other grafted rubber components, is characterized in that the particle size, weight average particle size, of the grafted rubber, is about 0.1 to 1.0 microns, preferably 0.1 to 0.6 microns. The grafted rubber may feature a bimodal size distribution of its rubber particles. In relevant embodiments, the particles of the “small mode” would have a weight average particle size in the range of 0.05 to 0.3, preferably 0.1 to 0.25 microns; the particles of the “large mode” would have a weight average particle size of 0.31 to 1.0, preferably 0.35 to 0.6 microns.
The substrate contains 1 to 50, preferably 3 to 40, percent relative to the weight of the substrate, of a core (A1) and 99 to 50, preferably 97 to 60, percent relative to the weight of the substrate of a shell (A2) where
(A1) denotes an optionally crosslinked core polymerized from at least one member selected from the group consisting of styrene, &agr;-methyl styrene, ring-halogenated styrene and ring-alkylated styrene, and where
(A2) denotes a shell enveloping said core comprising crosslinked C
1-18
-alkyl acrylate rubber, preferably C
2-8
-alkyl acrylate rubber, said substrate being present in particulate form having a size (weight average particle size) of about 0.05 to 1.0, preferably 0.1 to 0.6 microns.
The grafted phase (A3) contains a copolymer of at least one monomer selected from a first group consisting of styrene, &agr;-methyl styrene, ring-halogenated styrene and ring-alkylated styrene, such as p-methylstyrene and tert.butylstyrene with at least one monomer selected from a second group consisting of (meth)acrylonitrile, methylmethacrylate and maleic anhydride. The weight ratio between said monomer(s) of said first group to said monomer(s) of said second group of 85:15 to about 65:35.
The inventive composition preferably contains no additional grafted rubber components.
The composition according to the invention may contain conventional additives, in customary and effective amounts, which are known for their utility in thermoplastic elastomeric molding compositions.
The grafted rubber, component (A) of the inventive composition, may be prepared by graft copolymerization of at least one of styrene, &agr;-methyl styrene, ring halogenated styrene, ring-alkylated styrene, such as p-methylstyrene and tert.butylstyrene with at least one of (meth)acrylonitrile, methylmethacrylate and maleic anhydride in the presence of the crosslinked, elastomeric core-shell substrate. Since 100% grafting yield cannot be achieved in the graft copolymerization, the polymerization product from the graft copolymerization always contains a proportion of free, non-grafted copolymer (for convenience, the grafted phase is referred to hereinafter in this text as “SAN”). However, for the purposes of the present invention, the term “graft copolymer” is only applied to the rubber to which SAN have actually been grafted. The proportion of the grafted SAN in the polymerization product from the graft copolymerization can be determined in the conventional manner by extracting the free, non-grafted SAN copolymer from the polymerization product, for example, by methyl ethyl ketone, since the grafting base of the grafted rubber is crosslinked and the grafted copolymer is chemically bound to the graft base. The principles of the method of separation have been described by Moore, Moyer and Frazer, Appl. Polymer Symposia No. 7, page 67, et seq. (1968).
The degree of grafting, in the present context, refers to the percentage proportion, based on the total graft copolymer, of the SAN which is chemically bonded in the grafting branches of the graft copolymer. The degree of grafting may be calculated from the analytically determined composition of the gel which is insoluble in methyl ethyl ketone.
The particle size according to the invention is the weight-average particle size as determined by an ultracentrifuge, such as in accordance with the method of W
Chen Chuan-Ju
Sierodzinski Mitchell J.
Bayer Corporation
Buttner David J.
Gil Joseph C.
Preis Aron
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