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
2002-02-28
2004-04-13
Mullis, Jeffrey (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...
C525S087000
Reexamination Certificate
active
06720386
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to weatherable styrenics with improved translucency. More particularly, the invention relates to modified acrylate-styrene-acrylonitrile (ASA) plastics with improved translucency for better colorability.
2. Description of the Related Art
ASA polymers (also known as AAS), which are rubber and thermoplastic composites, have long been known and used in various outdoor applications which take advantage of the weatherability of such resins. ASA polymers are in general terpolymers of acrylate, styrene, and acrylonitrile having an excellent combination of impact and weatherability properties. These ASA resins typically contain a grafted crosslinked alkylacrylate rubber phase. Most ASA products consist of a two phase system of a grafted elastomeric terpolymer, acrylate-styrene-acrylonitrile, dispersed in a glassy continuous matrix of styrene-acrylonitrile (SAN) copolymer. The graft typically consists of a polyalkylacrylate rubber core and grafted SAN shell, small amounts of styrene and acrylonitrile being grafted onto the rubber particles to compatibilize the two phases.
In the ASA manufacturing process, three distinct polymerization reactions or stages are involved. First the elastomeric component, typically a polyalkyl acrylate rubber or polyalkyl alkylacrylate rubber, is produced. This phase can be carried out either in a water-based emulsion or in a solution polymerization process. In the second stage, the styrene and acrylonitrile are copolymerized optionally with other monomers and grafted onto the elastomeric phase to achieve the desired compatibility. This stage can be performed either in emulsion, bulk/mass or via suspension and/or the emulsion-suspension process route. In the third stage, styrene and acrylonitrile (and, optionally, other monomers) are copolymerized, either simultaneously with the second (grafting) stage or separately in an independent operation, to form the rigid matrix. Again, this step may involve one or more of the following processes: emulsion, bulk or suspension.
In addition, the ASA materials may be produced by other process techniques such as batch, semibatch and continuous polymerization for reasons of either manufacturing economics or product performance or both.
To alter specific properties of the resulting polymers, other acrylate, monovinylidene aromatic, and ethylenically unsaturated nitrile monomers may be incorporated, either in addition to or in place of the various acrylate-styrene-acrylonitrile components. The physical properties of ASA plastics vary somewhat with their method of manufacture but more so with their composition. Specific performance requirements and extensive material differentiation are achieved by manipulation of monomer composition, microstructure, morphology and/or additives.
However, due to a high level of opacity, weatherable ASA materials are difficult to color match in bright colors and may lack depth of color. In addition, coloring costs are usually high when matches are possible. There remains a need for improved ASA materials which maintain desirable properties which allow matching of bright colors at reduced pigment cost or production of intense colors with better depth of color.
There is a particular need for weatherable ASA plastics which allow matching of bright colors at reduced pigment cost or production of bright intense colors with better depth of color with reduced pigment usage while maintaining other desirable properties. Weatherable ASA materials with improved translucency that reduces opacity, resulting in better colorability can be prepared from SAN copolymer grafted alkyl acrylate rubber, preferably butyl acrylate rubber, with a matrix rigid phase prepared from polymethyl methacrylate (PMMA) and methyl methacrylate-styrene-acrylonitrile (MMASAN) terpolymer.
SUMMARY OF THE INVENTION
In one embodiment the present invention generally provides for an acrylate-styrene-acrylonitrile type (ASA) composition comprising:
a) a matrix phase comprising (i) a terpolymer of a vinyl carboxylic acid ester monomer, a vinyl aromatic monomer and a vinyl cyanide monomer and (ii) a polymethylmethacrylate (PMMA); and
b) a graft copolymer comprising (i) a substrate rubber and (ii) a superstrate copolymer, wherein the substrate rubber comprises a rubber derived from a vinyl carboxylic acid ester monomer and wherein the superstrate copolymer comprises a copolymer derived from both a vinyl aromatic monomer and a vinyl cyanide monomer,
wherein the matrix phase is present at a weight percent level of from about 75 to about 25 weight percent of the total weight of the composition; and
wherein the graft copolymer is present at a level of from about 25 to about 75 weight percent of the total weight of the composition, and the substrate rubber is present at a level of from about 5 to about 55 weight percent of the total weight of the composition.
In another embodiment the present invention generally provides for an acrylate-styrene-acrylonitrile type (ASA) composition comprising:
a) a continuous phase or matrix, frequently denoted a “rigid matrix phase,” comprising a mixture of:
1) MMASAN, a terpolymer of methyl methacrylate and styrene acrylonitrile ranging in weight percent composition of the continuous rigid phase of from about 90 weight percent to about 10 weight percent; and
2) PMMA, a homopolymer of methylmethacrylate, polymethylmethacrylate, ranging in weight percent composition of the continuous phase of from about 10 weight percent to about 90 weight percent; and
b) a discontinuous phase, dispersed in the continuous phase, comprising:
1) a core graft rubber where the core is butyl acrylate rubber comprising from about 15 to about 90 weight percent of the total core graft disperse phase and
2) a graft or superstrate polymer of styrene acrylonitrile (SAN) comprising from about 85 to about 10 weight percent of the total core graft disperse phase;
wherein the continuous or matrix phase comprises from about 90 to about 10 weight percent of the total composition; and
wherein the dispersed or discontinuous phase comprises from about 10 to about 90 weight percent of the total composition.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Weatherable ASA polymers with improved translucency, better colorability and color matching, reduced pigment costs and other desirable physical properties are prepared from poly (alkyl acrylate) rubber based ASA graft phase in combination with a vinyl aromatic/vinyl cyanide/vinyl carboxylic acid ester matrix phase.
As used herein, the terms “weatherable” and “weatherability” refer to the ability or property of a material to effectively withstand the conditions of an outdoor environment over a long period of time (years) with substantially no degradation or decomposition, that is, resistance to UV radiation and to exposure to cyclic variations in temperature and humidity.
The ASA polymers of the present invention comprise a two phase system. The two phase system comprises an acrylate rubber substrate, preferably poly (butyl acrylate) rubber, with a superstrate (or graft) copolymer of styrene-acrylonitrile (SAN) attached to it. This phase is commonly referred to as the “rubber graft phase” because the SAN is physically attached or grafted to the rubber through chemical reaction. A “rigid matrix phase” or continuous phase of PMMA/MMASAN is utilized. The rubber graft phase (or dispersed phase) is dispersed throughout the matrix phase PMMA/MMASAN which forms the polymer continuum. The rubber interface is the surface forming the boundaries between the graft and matrix phases. The grafted SAN acts as a compatibilizer between the rubber and the matrix phase PMMA/MMASAN at this interface and prevents the separation of these two otherwise immiscible phases.
It has been found that there is a synergistic effect in reducing opacity of the blend when PMMA/MMASAN mixture is used as compared to using PMMA or MMASAN alone. Weatherable ASA blends with bright intense colors, reduced usage of color pigments and/or achievement of better depth o
Gaggar Satish Kumar
Hongladarom Kwan
General Electric Company
Mullis Jeffrey
LandOfFree
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