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
2002-02-21
2003-06-03
Niland, Patrick D. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C523S201000, C523S206000, C523S209000, C525S534000
Reexamination Certificate
active
06573342
ABSTRACT:
BACKGROUND OF INVENTION
This invention relates to polymer dispersions in solid form and a method for their preparation. More particularly, it relates to the preparation of polymer blends in solid form.
The use of elastomeric (i.e., rubbery) polymers as additives in blends comprising other polymers is known. Various rubbery polymers are useful as impact modifiers, flame retardants and additives conferring other properties on blends in which they are incorporated. While the dispersion of liquid additives in polymeric powders is well known and previously documented by Dahms et al. (U.S. Pat. No. 3,301,813), a uniform and fine dispersion of rubbery polymers in thermoplastics to form dry free-flowing powders has not been reported.
U.S. Pat. Nos. 3,824,208, 5,153,238, 5,391,594 and 5,412,014 describe the incorporation of fillers such as silica in rubbery polymers to form compositions which exist as free-flowing particles. However, it is sometimes highly desirable to exclude inorganic materials such as silica from polymer blends or coat the surface of the silica particles with siloxane elastomers, in which case these compositions are no longer free-flowing. The surface chemistry of the filler in some cases can result in degradation of the matrix polymer.
Conventional approaches for obtaining free-flowing powders with elastomeric components include the use of block copolymers, core-shell copolymers or graft copolymers with thermoplastics. Copolymerization or grafting of glassy/crystalline thermoplastic prevents agglomeration of the rubbery component and enables convenient addition of these impact modifiers as free-flowing powders in extrusion equipment for melt processing. Such approaches however do not provide a cost effective solution for preparing free-flowing polymeric dispersions.
It is difficult, however, to prepare homogeneous blends of rubbery polymers with other resins, owing to the relative intractabilities of said rubbery polymers and the slow progress of dispersion of said polymer in the blend. Examples of some alternative approaches for obtaining free-flowing powders include mixing a dispersion of an organic thermoplastic polymer with an emulsion of a silicone resin as taught by Fuhr et al. in U.S. Pat. No. 5,100,958. This method is once again not cost effective since it involves a subsequent adjustment of pH for coagulation followed by isolation and drying of the coagulate. Another method proposed by Vaughn in U.S. Pat. No. 4,153,639 involves mixing the resin and the rubbery additive (in this case silicone gum) in a liquid medium having a component which vaporizes readily. The liquid medium is contacted with flowing live steam in a conduit and the mixture is fed into a closed chamber from which the superheated, vaporized liquid components are removed and a particulate blend is extracted.
Other practical limitations in melt—melt blending of thermoplastics with rubbery polymers include the inability to disperse the rubber phase adequately in the thermoplastic melt using the conventional processing equipment due to excessive shear heating in the extruders and a morphological balance between drop break up (dispersion) and the subsequent coalescence of the dispersed particles.
Some applications like powder coating require the availability of the thermoplastic resin blend in a powdery form. One route for the formation of thermoplastic blend powders involves high temperature melt extrusion of the various melt components followed by grinding of the thermoplastic pellets to obtain a free-flowing powder. The ability to directly form uniform thermoplastic blends with fine morphologies at lower processing temperatures can provide a direct, cost-effective and simpler process.
SUMMARY OF INVENTION
The present invention facilitates the formation of polymer blends as described herein above. In particular, it makes it possible to prepare blends which are solid and free-flowing, said blends comprising high and often major proportions of rubbery materials such as polyorganosiloxanes and synthetic elastomers, said blends also containing another resinous constituent. Among the blends that can be produced are those useful as products in their own right and those useful as master batches suitable for incorporation as additives in other polymer compositions.
In one of its aspects, the present invention provides a method for preparing a blend, said blend comprising: a polyorganosiloxane (A) having at least one of a glass transition temperature (Tg
a
) or a melting temperature (Tm
a
), a polyphenylene ether (B) having at least one of a glass transition temperature (Tg
b
) or melting temperature (Tm
b
), wherein Tg
a
<Tg
b
when polymers A and B are amorphous, Tm
a
<Tm
b
when both polymers A and B are crystalline, Tg
a
<Tm
b
when polymer A is amorphous and polymer B is crystalline, and Tm
a
<Tg
b
when polymer A is crystalline and polymer B is amorphous, which comprises intimately mixing said polymers at a suitable temperature between the lower of Tg
a
and Tm
a
and the value of Tg
b
, for a time and under shear conditions sufficient to convert polymer A to dispersed particles coated with polymer B and produce a free-flowing blend, said blend being free of silica filler and treated silica filler. Also provided is a composition prepared by the aforementioned method.
DETAILED DESCRIPTION
In some embodiments the present invention provides a method wherein Tg
a
is below about 160° C., in other embodiments below about 50° C., and in still other embodiments below about minus 100° C. In some embodiments the present invention provides a method wherein polymer B is crystalline. In still other embodiments the present invention provides a method wherein polymer B is amorphous and Tg
b
is above about 100° C. It is generally known to those skilled in the art that many, but not all, polymers as commonly obtained comprise a mixture of amorphous and crystalline fractions. In some particular polymers an amorphous phase predominates, while in other particular polymers a crystalline phase may provide a significant fraction of the total polymer. In other particular embodiments polymer A and polymer B are typically immiscible and incompatible with each other.
In various embodiments the present invention provides a method wherein polymer A is a polyorganosiloxane, an ethylene-propylene rubber, polybutadiene, polyisoprene, neoprene, an acrylic rubber, or copolymers thereof, and polymer B is an olefin polymer, a polycarbonate, poly(vinyl chloride), a linear polyester, a vinyl aromatic polymer, a polyphenylene ether, a polyimide, a polyethersulfone, a polyetherketone, a polyarylene sulfide, or copolymers thereof. In particular embodiments the present invention provides a method wherein polymer B is poly(2,6-dimethyl-1,4-phenylene ether), poly(butylene terephthalate), or polyetherimide.
Provided in yet another embodiment is a method wherein polymers A and B are mixed in a rotary blade mixer at a blade tip velocity in the range of about 1,000-15,000 cm/sec.
In another embodiment the instant invention provides a composition comprising a blend of polymer A having glass transition temperature (Tg
a
) and/or a melting temperature (Tm
a
), polymer B having glass transition temperature (Tg
b
) or melting temperature (Tm
b
), wherein Tg
a
<Tg
b
when polymers A and B are amorphous, Tm
a
<Tm
b
when both polymers A and B are crystalline, Tg
a
<Tm
b
when polymer A is amorphous and polymer B is crystalline, and Tm
a
<Tg
b
when polymer A is crystalline and polymer B is amorphous, said composition being produced by the process of intimately mixing said polymers at a suitable temperature between the lower of Tg
a
and Tm
a
and the higher of Tg
b
and Tm
b
, for a time and under shear conditions sufficient to convert polymer A to dispersed particles coated with polymer B and produce a free-flowing blend in the form of a powder. In still another embodiment the instant invention provides a composition comprising a blend of polymer A having glass transition temperature (Tg
a
) and/or a melting temperature (Tm
Anostario Joseph Michael
Singh Navjot
Cabou Christian G.
General Electric Company
Johnson Noreen C.
Niland Patrick D.
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