Thermoplastic vulcanizate compositions
In methods for forming thermoplastic vulcanizates, and thermoplastic vulcanizates formed by such methods, a masterbatch comprising one or more additives in a carrier resin comprising propylene- or ethylene-based copolymer is added to the thermoplastic vulcanizate formulation. The resulting thermoplastic vulcanizate may additionally be passed through a 200 mesh or finer screen and thereafter extruded. The thermoplastic vulcanizates may exhibit increased extrusion throughput rates and enhanced surface smoothness.
1. A method for preparing a thermoplastic vulcanizate, the method comprising:
dynamically vulcanizing at least a portion of an elastomer component in the presence of a thermoplastic resin and a curing agent so as to form a thermoplastic vulcanizate wherein the elastomer component is at least partially vulcanized and is dispersed in a continuous phase comprising the thermoplastic resin; and
introducing a carbon black masterbatch into the thermoplastic vulcanizate, wherein the carbon black masterbatch comprises carbon black particulates dispersed in a carrier resin comprising a propylene-α-olefin copolymer, the propylene-α-olefin copolymer comprising about 50 wt % to about 99 wt % propylene-derived units and about 1 wt % to about 35 wt % comonomer units derived from one of ethylene and a C 4 -C 10 alpha-olefin, and having a heat of fusion of about 75 J/g or less.
2. The method of claim 1 , wherein introducing the carbon black masterbatch into the thermoplastic vulcanizate comprises blending the carbon black masterbatch with the thermoplastic vulcanizate while the thermoplastic vulcanizate remains in a molten state following the dynamic vulcanization.
3. The method of claim 1 , further comprising pelletizing the thermoplastic vulcanizate so as to form a plurality of thermoplastic vulcanizate pellets prior to introducing the carbon black masterbatch to the thermoplastic vulcanizate.
4. The method of claim 3 , wherein introducing the carbon black masterbatch with the thermoplastic vulcanizate comprises melt-mixing the thermoplastic vulcanizate pellets with the carbon black masterbatch.
5. The method of claim 1 , further comprising melt-mixing the propylene-α-olefin copolymer and the carbon black, and forming a plurality of masterbatch pellets comprising the carbon black dispersed in the propylene-α-olefin copolymer carrier resin, such that the masterbatch pellets are used as the carbon black masterbatch that is introduced to the thermoplastic vulcanizate.
6. The method of claim 1 , further comprising passing the thermoplastic vulcanizate through a 200 U.S. Mesh (74 micron) or finer screen after introducing the carbon black masterbatch.
7. The method of claim 1 , wherein the thermoplastic vulcanizate comprises less than or equal to 4 wt % of the propylene-α-olefin copolymer, by weight of the thermoplastic vulcanizate, after introducing the carbon black masterbatch.
8. The method of claim 1 , wherein the thermoplastic vulcanizate has a surface spot count less than or equal to 9 blemishes in a 1 in.×18 in. (2.54 cm×45.72 cm) extruded strip of the thermoplastic vulcanizate.
9. The method of claim 1 , wherein the thermoplastic vulcanizate has an extrusion throughput rate that is about 2% to about 15% faster as compared to an otherwise identical thermoplastic vulcanizate in which all carrier resin comprising the propylene-α-olefin copolymer is instead a homopolypropylene carrier resin.
10. A thermoplastic vulcanizate formed according to the method of claim 1 .