Patent Publication Number: US-2006014903-A1

Title: Thermoplastic vulcanizates with enhanced cooling and articles made therefrom

Description:
BACKGROUND  
      1. Field of Inventions  
      Embodiments of the present inventions generally relate to thermoplastic vulcanizates and articles made therefrom.  
      2. Description of Related Art  
      Thermoplastic vulcanizates (TPVs) may be characterized by finely divided rubber particles dispersed within a plastic matrix. These rubber particles are crosslinked to promote elasticity. As such, TPVs exhibit the processing properties of the plastic and the elasticity of the rubber.  
      TPVs are conventionally produced by dynamic vulcanization. Dynamic vulcanization is a process whereby a rubber component is crosslinked or vulcanized within a blend of at least one non-vulcanizing polymer component while undergoing mixing or masticating at some elevated temperature. Preferably, the temperature of this curing step is greater than the melt temperature of the non-vulcanizing polymer component.  
      TPVs are useful for forming extruded articles for use in automotive, industrial, and consumer markets. Some of these uses require extruded articles having thick cross sections of TPV. Such thick sections are slow to cool at extrusion temperatures causing incomplete crystallization through the cross section thereby reducing optimal performance. Therefore, there is a need to enhance cooling of the TPV without sacrificing the flexibility, processability, and mechanical performance of the TPV and the articles extruded therefrom.  
     SUMMARY  
      A thermoplastic vulcanizate (TPV) composition and articles for using the same are provided. In one or more embodiments, the TPV includes a dispersed, at least partially vulcanized rubber component; an unvulcanized, or non-crosslinked, thermoplastic component; and a nucleating agent, wherein the composition has a Shore A Hardness of at least 60 and a Shore D Hardness less than 50. Preferably, the thermoplastic component is unvulcanized or non-crosslinked.  
      An extruded article is also provided. In one or more embodiments, this article comprises the thermoplastic vulcanizate composition that includes the dispersed, at least partially vulcanized rubber component; the thermoplastic component; and the nucleating agent. The thermoplastic vulcanizate composition has a Shore A hardness of at least 60 and a Shore D hardness less than 50. Preferably, the extruded article is elongated and has a wall thickness of at least 5 mm.  
      A flexible conduit, such as cable or pipeline, is also provided. In one or more embodiments, the conduit comprises an inner housing having a channel formed therethrough; at least one tensile layer at least partially disposed about the inner housing; and the thermoplastic vulcanizate composition at least partially disposed about the at least one tensile layer. The thermoplastic vulcanizate composition includes the dispersed, at least partially vulcanized rubber component; the thermoplastic component; and the nucleating agent. The thermoplastic vulcanizate composition has a Shore A hardness of at least 60 and a Shore D hardness less than 50, and also has a wall thickness of at least 5 mm.  
      An underwater conduit, such as marine cable or pipeline, is further provided. In one or more embodiments, the conduit comprises a tubular having an annulus formed therethrough; at least one tensile layer at least partially disposed about the inner housing; and an outer covering at least partially disposed about the at least one tensile layer. The outer covering comprises the dispersed, at least partially vulcanized rubber component; the isotactic polypropylene component; and the nucleating agent, particularly including one comprising sodium 2,2′-methylene-bis-(2,6-di-tert-butylphenyl)phosphate or norbornane (bicyclo(2.2.1)heptane carboxylic acid salt. The outer covering has a Shore A hardness of at least 60 and a Shore D hardness less than 50, and also has a wall thickness of at least 5 mm. 
    
    
     BRIEF DESCRIPTION OF THE FIGURE  
      A specfic embodiment of the invention, and of a use of the invention compounds, is represented in the attached illustration:  
       FIG. 1  is a cross-sectional view of an exemplary pipe or conduit having an outer covering made of the invention composition.  
    
    
     DETAILED DESCRIPTION  
      Definitions and Properties  
      Each of the inventions will now be described in greater detail below, including specific embodiments, versions and examples, but the inventions are not limited to these embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the inventions, when the information in this patent is combined with available information and technology.  
      Various terms as used herein are defined below. To the extent a term used in a claim is not defined below, it should be given the broadest definition persons in the pertinent art have given that term as reflected in one or more printed publications or issued patents.  
      The term “thermoplastic vulcanizate composition” (also referred to as simply thermoplastic vulcanizate or TPV) is broadly defined as any material that includes a dispersed, at least partially vulcanized, rubber component; a thermoplastic component; and an additive oil. A TPV material may further include other ingredients, other additives, or both.  
      The term “vulcanizate” means a composition that includes some component (e.g., rubber component) that has been vulcanized. The term “vulcanized” is defined herein in its broadest sense, as reflected in any issued patent, printed publication, or dictionary, and refers in general to the state of a composition after all or a portion of the composition (e.g., crosslinkable rubber) has been subjected to some degree or amount of vulcanization. Accordingly, the term encompasses both partial and total vulcanization. A preferred type of vulcanization is “dynamic vulcanization,” discussed below, which also produces a “vulcanizate.” Also, in at least one specific embodiment, the term vulcanized refers to more than insubstantial vulcanization, e.g., curing (crosslinking) that results in a measurable change in pertinent properties, e.g., a change in the melt flow index (MFI) of the composition by 10% or more (according to any ASTM-1238 procedure). In at least that context, the term vulcanization encompasses any form of curing (crosslinking), both thermal and chemical, that can be utilized in dynamic vulcanization.  
      The term “dynamic vulcanization” means vulcanization or curing of a curable rubber blended with a thermoplastic resin under conditions of shear at temperatures sufficient to plasticize the mixture. In at least one embodiment, the rubber is simultaneously crosslinked and dispersed as micro-sized particles within the thermoplastic component. Depending on the degree of cure, the rubber to thermoplastic component ratio, compatibility of rubber and thermoplastic component, the kneader type and the intensity of mixing (shear rate), other morphologies, such as co-continuous rubber phases in the plastic matrix, are possible.  
      As the term is used herein, a “partially vulcanized” rubber is one wherein more than 5 weight percent (wt %) of the crosslinkable rubber is extractable in boiling xylene, subsequent to vulcanization (preferably dynamic vulcanization), e.g., crosslinking of the rubber phase of the thermoplastic vulcanizate. For example, less than 5 wt %, or less than 20 wt %, or less than 30 wt %, or less than 50 wt % of the crosslinkable rubber may be extractable from the specimen of the thermoplastic vulcanizate in boiling xylene. The percentage of extractable rubber can be determined by the technique set forth in U.S. Pat. No. 4,311,628, and the portions of that patent referring to that technique are hereby incorporated by reference.  
      Preferably, the percent of soluble rubber in the cured composition is determined by refluxing a specimen in boiling xylene, weighing the dried residue and making suitable corrections for soluble and insoluble components based upon knowledge of the composition. Thus, corrected initial and final weights are obtained by subtracting from the initial weight the weight of the soluble components, other than the rubber to be vulcanized, such as extender oils, plasticizers and components of the compositions soluble in organic solvent, as well as that rubber component of the TPV that it is not intended to cure. Any insoluble pigments, fillers, etc., are subtracted from both the initial and final weights. Any materials in the uncured rubber that are soluble in refluxing xylene or any ethylene-propylene copolymer containing no unsaturation (no termonomer) are regarded as being non-crosslinkable components of the rubber which quantities are subtracted from the rubber when calculating the percent of soluble rubber in a cured composition, up to about 5 weight percent, typically between about 0.5 to about 2.0 weight percent, of EPDM rubber is soluble in refluxing xylene.  
      A “fully vulcanized” (or fully cured or fully crosslinked) rubber is one wherein less than 5 weight percent (wt %) of the crosslinkable rubber is extractable in boiling xylene or cyclohexane, subsequent to vulcanization (preferably dynamic vulcanization), e.g., crosslinking of the rubber phase of the thermoplastic vulcanizate. Preferably, less than 4 wt % or less, or 3 wt % or less, or 2 wt % or less, or 1 wt % or less of the crosslinkable rubber is extractable in boiling xylene or cyclohexane.  
      The term “polypropylene” as used herein broadly means any polymer that is considered a “polypropylene” by persons skilled in the art (as reflected in at least one patent or publication). Preferably, the polypropylene used in the compositions described herein that has a melting point above 110° C. includes at least 90 wt % propylene units and contains isotactic sequences of those units. Alternatively, instead of isotactic polypropylene, a composition may include a syndiotactic polypropylene, which in certain cases can have a melting point above 110° C. The polypropylene can either be derived exclusively from propylene monomers (i.e., having only propylene units) or be derived from mainly propylene (more than 80% propylene) with the remainder derived from olefins, particularly ethylene, and/or C 4 -C 10  α-olefins. As noted elsewhere herein, certain polypropylenes have a high MFI (e.g., from a low of 10, or 15, or 20 g/10 min to a high of 25 to 30 g/10 min. Others have a lower MEI, e.g., “fractional” polypropylenes which have an MFI less than 1.0. Those with high MFI may be preferred for ease of processing or compounding.  
      The term “nucleating agent” means any additive that produces a nucleation site for thermoplastic crystals to grow from a molten state to a solid, cooled structure. In other words, nucleating agents provide sites for growing thermoplastic crystals upon cooling the thermoplastic from its molten state.  
      Specific Embodiments  
      Various specific embodiments are described below, at least some of which are also recited in the claims. For example, at least one specific embodiment is directed to a thermoplastic vulcanizate having an at least partially vulcanized rubber component dispersed within a thermoplastic component, and a nucleating agent for controlling crystallization. The amount of the rubber component and the amount of the thermoplastic component is controlled such that the thermoplastic vulcanizate composition has a Shore A hardness of at least 60 and a Shore D hardness less than 50.  
      For example, in one or more embodiments, the rubber component is present in the amount of from about 5 weight percent (wt %) to about 85 wt % based upon the total weight of rubber and thermoplastic. In one or more embodiments, the rubber component is present in the amount of less than 70 wt % or less than 50 wt % based upon the total weight of rubber and thermoplastic. In one or more embodiments, the thermoplastic component is present in the amount of from about 15 wt % to about 95 wt % based upon the total weight of rubber and thermoplastic. In one or more embodiments, the thermoplastic component is present in the amount of more than 30 wt % or more than 50 wt % based upon the total weight of rubber and thermoplastic. In one or more embodiments, the nucleating agent is present in an amount sufficient to induce crystallization to produce the described TPV compositions. In one or more embodiments, the nucleating agent is present in the amount of from about 0.05 wt % to about 5 wt % based on the total weight of the composition or the total weight of the thermoplastic component. In one or more embodiments, the nucleating agent is present in the amount of from less than 3 wt %, or less than 2 wt %, or less than 1 wt %, or less than 0.5 wt % based on the total weight of the composition or the total weight of the thermoplastic component.  
      In one or more embodiments, these TPV compositions have a Shore-A Hardness of greater than 60, greater than 70, or greater than 80. These TPV compositions also have a Shore-D Hardness of less than 50, less than 40, or less than 30. In one or more embodiments, the Shore-A Hardness may range from a low of 60, 65, or 70 to a high of 75, 80, or 90. In one or more embodiments, the Shore-D Hardness may range from a low of 5, 10, or 15 to a high of 40, 45, or 50. Those Shore Hardness values are measured according to ASTM D-2240.  
      Surprisingly, those hardness values are achieved without sacrificing other important mechanical properties, and also without the need to add amounts of oil that cause oil seepage. Also surprising is that those Shore-A Hardness and Shore-D Hardness values are achieved without sacrificing ease of processability. For examples, those TPV compositions have a Tensile Strength (TS) measured in accordance with ASTM D412 (ISO 37), ranging from 10 to 25 MPa, or more narrowly from 11 to 16 MPa. Those TPV compositions also have an Elongation at break measured in accordance with ASTM D412 (ISO 37), ranging from a low of 50%, 70%, or 100% to a high of 200%, 400% or 700%. Those TPV compositions also have a 100% Modulus, also measured in accordance with ASTM D412 (ISO 37), ranging from a low of 10 MPa to a high of 15 MPa, more narrowly from 11 to 14 MPa, and more narrowly from 12 MPa to 13 MPa.  
      Nucleating Agent  
      The nucleating agent provides a plurality of nucleating sites for the thermoplastic component to crystallize when cooled. Surprisingly, this plurality of nucleating sites promotes even crystallization within the thermoplastic vulcanizate composition, allowing the composition to crystallize throughout an entire cross section in less time and at higher temperature. This plurality of nucleating sites produces a greater amount of smaller crystals within the thermoplastic vulcanizate composition which require less cooling time.  
      This even cooling distribution has many advantages and is extremely beneficial in extruded articles of the TPVs described herein having a thickness greater than 2 mm, such as greater than 5 mm, greater than 10 mm, and even greater than 15 mm. Extruded articles of the TPV described can have thicknesses greater than 20 mm and still exhibit effective cooling (i.e. cooling from an outer surface of the cross section to an inner surface of the cross section) at extrusion temperatures without sacrificing mechanical strength. Such extrusion temperatures typically will be at or above the melting point of the thermoplastic component.  
      Illustrative nucleating agents include, but are not limited to dibenzylidene sorbitol based compounds, sodium benzoate, sodium phosphate salts, as well as lithium phosphate salts. For example, the nucleating agent may include sodium 2,2′-methylene-bis-(2,6-di-tert-butylphenyl)phosphate which is commercially available from Milliken &amp; Company. Another specific nucleating agent is norbornane (bicyclo(2.2.1)heptane carboxylic acid salt, which is commercially available from CIBA Specialty Chemicals.  
      Thermoplastic Component  
      The “thermoplastic component” may be any material that is not a “rubber” (as defined herein) and that is a polymer or polymer blend considered by persons skilled in the art as being thermoplastic in nature, e.g., a polymer that softens when exposed to heat and returns to its original condition when cooled to room temperature. The thermoplastic component may contain one or more polyolefins. Useful polyolefins include thermoplastic, crystalline polyolefin homopolymers and copolymers. Illustrative polyolefins may be prepared from mono-olefin monomers including, but are not limited to, monomers having 2 to 7 carbon atoms, such as ethylene, propylene, 1-butene, isobutylene, 1-pentene, 1-hexene, 1-octene, 3-methyl-1-pentene, 4-methyl-1-pentene, 5-methyl-1-hexene, mixtures thereof and copolymers thereof with (meth)acrylates and/or vinyl acetates. The thermoplastic component may be added to the composition alone, or in a blend of two or more polypropylenes, polyethylenes, other polyolefins, derivatives thereof, or any combination thereof. Preferably, the thermoplastic component is unvulcanized or non cross-linked.  
      In one or more embodiments, the thermoplastic component contains polypropylene. Preferably, the thermoplastic component contains isotactic polypropylene. A preferable isotactic polypropylene has a weight average molecular weight from about 200,000 to about 600,000, and a number average molecular weight from about 80,000 to about 200,000. A more preferable isotactic polypropylene has a weight average molecular weight from about 300,000 to about 500,000, and a number average molecular weight from about 90,000 to about 150,000. In one or more embodiments, the isotactic polypropylene has a molecular weight distribution (Mw/Mn) (MWD), also referred to as “polydispersity index” (PDI), within a range having a low 1.5, 1.8. or 2.0 and a high of 4.5, 5, 10, 20, or 40.  
      The isotactic polypropylene preferably has a melt temperature (T m ) ranging from a low of 150° C., 155° C., or 160° C. to a high of 160° C., 170° C., or 175° C. The isotactic polypropylene preferably has a glass transition temperature (T g ) ranging from a low of −5° C., −3° C., or 0° C. to a high of 2° C., 5° C., or 10° C. The crystallization temperature (T c ) of the isotactic polypropylene component preferably ranges from a low of about 95° C., 100° C., or 105° C. to a high of about 110° C., 120° C. or 130° C., as measured by differential scanning calorimetry (DSC) at 10° C./min. Furthermore, the isotactic polypropylene preferably has a crystallinity of at least 25 percent as measured by differential scanning calorimetry.  
      In one or more embodiments, the isotactic polypropylene has a melt flow rate of less than about 10 dg/min, preferably less than about 2 dg/min, and still more preferably less than about 1.0 dg/min. A preferred isotactic polypropylene has a heat of fusion of greater than 75 J/g, or greater than 80 J/g, or greater than 90 J/g.  
      In one or more embodiments, the isotactic polypropylene has a density of from about 0.85 g/cc to about 0.93 g/cc. In one or more embodiments, the isotactic polypropylene has a density of from about 0.88 to about 0.92 g/cc. In one or more embodiments, the isotactic polypropylene has a density of from about 0.90 to about 0.91 g/cc.  
      Such an isotactic polypropylene may be synthesized using any polymerization technique known in the art such as, but not limited to, the “Phillips catalyzed reactions,” conventional Ziegler-Natta type polymerizations, and single-site organometallic compound catalysis, such as metallocene catalysis, for example. Illustrative metallocene catalyst compounds include, but are not limited to, the reaction products of metallocene-alumoxane and metallocene-ionic activator reagents. Illustrative polymerization methods include, but are not limited to, slurry, bulk phase, solution phase, and any combination thereof. Polymerization may be carried out by a continuous or batch process in a single stage, such as a single reactor, or in two or more stages, such as in two or more reactors arranged in parallel or series.  
      Rubber Component  
      The “rubber component” may be any material that is considered by persons skilled in the art to be a “rubber,” preferably a crosslinkable rubber (e.g., prior to vulcanization) or crosslinked rubber (e.g., after vulcanization). In addition to natural rubber, specific rubber components include, without limitation, any olefin-containing rubber such as ethylene-propylene copolymers (EPM), including particularly saturated compounds that can be vulcanized using free radical generators such as organic peroxides, as noted in U.S. Pat. No. 5,177,147, which is incorporated by reference in pertinent part. Other rubber components are ethylene-propylene-diene (EPDM) rubber, or EPDM-type rubber. An EPDM-type rubber can be a terpolymer derived from the polymerization of at least two different monoolefin monomers having from 2 to 10 carbon atoms, preferably 2 to 4 carbon atoms, and at least one poly-unsaturated olefin having from 5 to 20 carbon atoms. Those monoolefins desirably have the formula CH 2 ≡CH—R where R is H or an alkyl of 1-12 carbon atoms and are preferably ethylene and propylene. Desirably the repeat units from at least two monoolefins (and preferably from ethylene and propylene) are present in the polymer in weight ratios of 25:75 to 75:25 (ethylene:propylene) and constitute from about 90 to about 99.6 weight percent of the polymer. The polyunsaturated olefin can be a straight chained, branched, cyclic, bridged ring, bicyclic, fused ring bicyclic compound etc., and preferably is a nonconjugated diene. Desirably repeat units from the nonconjugated polyunsaturated olefin are from about 0.4 to about 10 weight percent of the rubber.  
      Another type of rubber component is butyl rubber. The term “butyl rubber” includes a polymer that predominantly includes repeat units from isobutylene but also includes a few repeat units of a monomer that provides a site for crosslinking. Monomers providing sites for crosslinking include a polyunsaturated monomer such as a conjugated diene or divinyl benzene. Desirably, from about 90 to about 99.5 weight percent of the butyl rubber are repeat units derived from the polymerization of isobutylene, and from about 0.5 to about 10 weight percent of the repeat units are front at least one polyunsaturated monomer having from 4 to 19 carbon atoms. Preferably the polyunsaturated monomer is isoprene or divinylbenzene. The polymer may be halogenated to further enhance reactivity in crosslinking. Preferably the halogen is present in amounts from about 0.1 to about 10 weight percent, more preferably about 0.5 to about 3.0 weight percent based upon the weight of the halogenated polymer; preferably the halogen is chlorine or bromine. The brominated copolymer of p-alkylstyrene, having from about 9 to 12 carbon atoms, and an isomonoolefin, having from 4 to 7 carbon atoms, desirably has from about 88 to about 99 weight percent isomonoolefin, more desirably from about 92 to about 98 weight percent, and from about 1 to about 12 weight percent p-alkylstyrene, more desirably from about 2 to about 8 weight percent based upon the weight of the copolymer before halogenation. Desirably the alkylstyrene is p-methylstyrene and the isomonoolefin is isobutylene. Desirably the percent bromine is from about 0.2 to about 8, more desirably from about 0.2 to about 3 weight percent based on the weight of the halogenated copolymer. The copolymer is a complementary amount, i.e., from about 92 to about 99.8, more desirably from about 97 to about 99.8 weight percent. These polymers are commercially available from, for example, ExxonMobil Chemical Co.  
      Except as stated otherwise, the term “copolymer” means polymers derived from two or more monomers (including terpolymers, tetrapolymers, etc.), and the term “polymer” refers to carbon-containing compounds having repeat units from one or more different monomers.  
      EPDM, butyl and halobutyl rubbers are rubbers low in residual unsaturation and are preferred when the vulcanizate needs good thermal stability or oxidative stability. The rubbers low in residual unsaturation desirably have less than 10 weight percent repeat units having unsaturation. Desirably excluded are acrylate rubber and epichlorohydrin rubber.  
      Other non-limiting examples of rubber components are halobutyl rubbers and halogenated (e.g., brominated) rubber copolymers of p-alkylstyrene and an isomonoolefin having from 4 to 7 carbon atoms (e.g. isobutylene). Still other examples are rubber homopolymers of conjugated dienes having from 4 to 8 carbon atoms and rubber copolymers having at least 50 weight percent repeat units from at least one conjugated diene having from 4 to 8 carbon atoms.  
      Rubber components can also be natural rubbers or synthetic homo or copolymers of at least one conjugated diene. Those rubbers are higher in unsaturation than EPDM rubber or butyl rubber. Those rubbers can optionally be partially hydrogenated to increase thermal and oxidative stability. Desirably those rubbers have at least 50 weight percent repeat units from at least one conjugated diene monomer having from 4 to 8 carbon atoms. Comonomers that may be used include vinyl aromatic monomer(s) having from 8 to 12 carbon atoms and acrylonitrile or alkyl-substituted acrylonitrile monomer(s) having from 3 to 8 carbon atoms. Other comonomers desirably include repeat units from monomers having unsaturated carboxylic acids, unsaturated dicarboxylic acids, unsaturated anhydrides of dicarboxylic acids, and include divinylbenzene, alkylacrylates and other monomers having from 3 to 20 carbon atoms.  
      Rubber components can also be synthetic rubber, which can be nonpolar or polar depending on the comonomers. Examples of synthetic rubbers include synthetic polyisoprene, polybutadiene rubber, styrene-butadiene rubber, butadiene-acrylonitrile rubber, etc. Amine-functionalized, carboxy-functionalized or epoxy-functionalized synthetic rubbers may be used, and examples of these include maleated EPDM, and epoxy-functionalized natural rubbers. These materials are commercially available. Non-polar rubbers are preferred; polar rubbers may be used but may require the use of one or more compatibilizers, as is well known to those skilled in the art.  
      A list of preferred rubber components include ethylene-propylene-diene rubber, natural rubber, butyl rubber, halobutyl rubber, halogenated rubber copolymer of p-alkystyrene and at least one isomonoolefin having 4 to 7 carbon atoms, a copolymer of isobutylene and divinyl-benzene, a rubber homopolymer of a conjugated diene having from 4 to 8 carbon atoms, a rubber copolymer having at least 50 weight percent repeat units from at least one conjugated diene having from 4 to 8 carbon atoms and a vinyl aromatic monomer having from 8 to 12 carbon atoms, or acrylonitrile monomer, or an alkyl substituted acrylonitrile monomer having from 3 to 8 carbon atoms, or an unsaturated carboxylic acid monomer, or an unsaturated anhydride of a dicarboxylic acid, or combinations thereon.  
      Rubber Curing Agents  
      Any curative that is capable of curing or crosslinking the rubber component may be used. Illustrative curatives include, but are not limited to, phenolic resins, peroxides, maleimides, and silicon-containing curatives. Depending on the rubber employed, certain curatives may be preferred. For example, where elastomeric copolymers containing units deriving from vinyl norbornene are employed, a peroxide curative may be preferred because the required quantity of peroxide will not have a deleterious impact on the engineering properties of the thermoplastic phase of the thermoplastic vulcanizate. In other situations, however, it may be preferred not to employ peroxide curatives because they may, at certain levels, degrade the thermoplastic components of the thermoplastic vulcanizate.  
      Phenolic resins are described U.S. Pat. Nos. 2,972,600; 3,287,440; and 6,433,090, which are incorporated herein in this regard. The preferred phenolic resin curatives can be referred to as resole resins and are made by condensation of alkyl substituted phenols or unsubstituted phenols with aldehydes, preferably formaldehydes, in an alkaline medium or by condensation of bi-functional phenoldialcohols. The alkyl substituents of the alkyl substituted phenols typically contain 1 to about 10 carbon atoms. Dimethylol phenols or phenolic resins, substituted in para-positions with alkyl groups containing 1 to about 10 carbon atoms are preferred. These phenolic curatives are typically thermosetting resins and may be referred to as phenolic resin curatives or phenolic resins. These phenolic resins are ideally used in conjunction with a catalyst system. For example, non-halogenated phenol curing resins are preferably used in conjunction with halogen donors and, optionally, a hydrogen halide scavenger. Where the phenolic curing resin is halogenated, a halogen donor is not required but the use of a hydrogen halide scavenger, such as ZnO, is preferred. For a further discussion of phenolic resin curing of thermoplastic vulcanizates, reference can be made to U.S. Pat. No. 4,311,628, which is incorporated herein by reference.  
      Useful silicon-containing curatives generally include silicon hydride compounds having at least two SiH groups. These compounds react with carbon-carbon double bonds of unsaturated polymers in the presence of a hydrosilation catalyst. Silicon hydride compounds that are useful in practicing the present invention include, but are not limited to, methylhydrogen polysiloxanes, methylhydrogen dimethyl-siloxane copolymers, alkyl methyl polysiloxanes, bis(dimethylsilyl)alkanes, bis(dimethylsilyl)benzene, and mixtures thereof.  
      Peroxide curatives are generally selected from organic peroxides. Examples of organic peroxides include, but are not limited to, di-tert-butyl peroxide, dicumyl peroxide, t-butylcumyl peroxide, alpha,alpha-bis(tert-butylperoxy)diisopropyl benzene, 2,5 dimethyl 2,5-di(t-butylperoxy)hexane, 1,1-di(t-butylperoxy)-3,3,5-trimethyl cyclohexane, -butyl-4,4-bis(tert-butylperoxy)valerate, benzoyl peroxide, lauroyl peroxide, dilauroyl peroxide, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexene-3, and mixtures thereof. Also, diaryl peroxides, ketone peroxides, peroxydicarbonates, peroxyesters, dialkyl peroxides, hydroperoxides, peroxyketals and mixtures thereof may be used. For a further discussion of peroxide curatives and their use for preparing thermoplastic vulcanizates, reference can be made to U.S. Pat. No. 5,656,693, which is incorporated herein by reference.  
      Additive Oil  
      The term “additive oil” includes both “process oils” and “extender oils.” For example, “additive oil” may include hydrocarbon oils and plasticizers, such as organic esters and synthetic plasticizers. Many additive oils are derived from petroleum fractions, and have particular ASTM designations depending on whether they fall into the class of paraffinic, naphthenic, or aromatic oils. Other types of additive oils include alpha olefinic synthetic oils, such as liquid polybutylene, e.g., products sold under the trademark Parapol®. Additive oils other than petroleum based oils can also be used, such as oils derived from coal tar and pine tar, as well as synthetic oils, e.g., polyolefin materials (e.g., Nexbase™, supplied by Fortum Oil and Gas Oy). Certain rubber components (e.g., EPDMs, such as Vistalon 3666) include additive oil that is preblended before the rubber component is combined with the thermoplastic. The type of additive oil utilized will be that customarily used in conjunction with a particular rubber component.  
      The ordinarily skilled chemist will recognize which type of oil should be used with a particular rubber, and also be able to determine the amount (quantity) of oil. The additive oil can be present in amounts from about 5 to about 300 parts by weight per 100 parts by weight of the blend of the rubber and isotactic polypropylene components. The amount of additive oil may also be expressed as from about 30 to 250 parts, and more desirably from about 70 to 200 parts by weight per 100 parts by weight of the rubber component. Alternatively, the quantity of additive oil can be based on the total rubber content, and defined as the ratio, by weight, of additive oil to total rubber in the TPV, and that amount may in certain cases be the combined amount of process oil (typically added during processing) and extender oil (typically added after processing). The ratio may range, for example, from about 0 to about 4.0/1. Other ranges, having any of the following lower and upper limits, may also be utilized: a lower limit of 0.4/1, or 0.6/1, or 0.8/1, or 1.0/1, or 1.2/1, or 1.5/1, or 1.8/1, or 2.0/1, or 2.5/1; and an upper limit (which may be combined with any of the foregoing lower limits) of 4.0/1, or 3.8/1, or 3.5/1, or 3.2/1, or 3.0/1, or 2.8/1. Larger amounts of additive oil can be used, although the deficit is often reduced physical strength of the composition, or oil weeping, or both.  
      Other Additives  
      The thermoplastic vulcanizate composition may further include one or more additives. Illustrative additives include, but are not limited, to particulate fillers, lubricants, antioxidants, antiblocking agents, stabilizers, anti-degradants, anti-static agents, waxes, foaming agents, pigments, flame retardants, processing aids, adhesives, tackifiers, plasticizers, wax, and discontinuous fibers (such as world cellulose fibers). Exemplary particulate fillers are carbon black, silica, titanium dioxide, calcium carbonate, colored pigments, clay, and combinations thereof. When non-black fillers are used, it may be desirable to include a coupling agent to compatibilize the interface between the non-black fillers and polymers. Desirable amounts of carbon black, or other colorants, when present, are from about 5 to about 250 parts by weight per 100 parts by weight of rubber.  
      Process Description  
      In one or more embodiments, the TPV is prepared by melt-mixing in any order, the thermoplastic component, the rubber component, and any additive in a mixer heated to above the melting temperature of the polypropylene component. The mixing equipment can include Banbury™ mixers, Brabender™ mixers, multiroll mills and melt mixing extruders, for example.  
      After sufficient molten-state mixing to form a well mixed blend, one or more curatives are added. In one or more embodiments, it is preferred to add the one or more curatives in solution with a liquid, such as a rubber processing oil or in a masterbatch, for example, which is compatible with the other components. It is convenient to follow the progress of crosslinking (vulcanization) by monitoring mixing torque or mixing energy requirements during mixing. The mixing torque or mixing energy curve generally goes through a maximum after which mixing can be continued somewhat longer to improve the fabricability of the blend.  
      Crosslinking (vulcanization) of the rubber can occur in a few minutes or less depending on the mix temperature, shear rate, and activators present for the curative. Suitable curing temperatures include from about 120° C. or 150° C. to about 250° C., more preferred temperatures are from about 150° C. or 170° C. to about 425° C. or 250° C. The one or more nucleating agents can be added before, during, or after vulcanization. After discharge from the mixer, the blend containing the at least partially vulcanized rubber dispersed in the polypropylene component along with the one or more nucleating agents can be milled, chopped, extruded, pelletized, injection-molded, or processed by any other desirable technique.  
      Articles  
      The thermoplastic vulcanizate composition is useful for making a variety of articles including, but not limited to, conduits, pipes, tubing, hoses, tires, belts, gaskets, moldings and molded parts, for example. The thermoplastic vulcanizate composition is useful for making articles by extrusion, injection molding, blow molding, and compression molding techniques. Preferably, the thermoplastic vulcanizate composition is useful for making articles by extrusion, and more preferably elongated, extruded articles having lengths greater than 1 meter, such as greater than 50 meters, greater than 100 meters, or greater than 1,000 meters, for example. In one particular embodiment, the thermoplastic vulcanizate composition may be useful as a covering or sheath (i.e. jacket) disposed about an elongated conduit for transporting fluids, such as oil and gas related fluids for example. The thermoplastic vulcanizate composition may also be useful as a covering or jacket disposed about cables containing electrical power cables, electrical conductors, fiber optics, data lines, or other communication lines, and combinations or bundles thereof. The thermoplastic vulcanizate composition may further be useful for securing wires, ropes, etc.  
       FIG. 1  shows a cross-sectional view of an exemplary pipe or conduit  100  having an outer covering made of the TPV described above. The conduit  100  includes an inner tube  110  having a channel or bore  105  formed therethrough. The tube  110  is made of a flexible material and includes a helically wound flat or profiled metallic strips to provide collapse resistance. A polymeric sheath  120  is at least partially disposed or wrapped around the tube  110  for containing the fluid in the pipe. The sheath  120  is preferably made of an impervious polymeric material. A layer  130  is at least partially disposed or wrapped around the layer  120  and provides resistance to internal pressure, hydrostatic collapse and crush. The layer  130  can be formed by helically wrapping a continuous metallic strip, preferably formed of carbon steel, with adjacent windings being interlocked, to form a flexible layer that provides significant hoop and axial strength, such as FLEXLOK™, commercially available from Wellstream, Inc.  
      An inner tensile layer  140  is at least partially disposed or wrapped around the layer  130 , and an outer tensile layer  150  is at least partially disposed or wrapped around the layer  140 . Each layer  140  and  150  includes at least one tensile reinforcement element that is wound to resist the hoop stress, the axial component of the internal pressure, and the axial load due to the weight of the suspended pipe and exterior effects. Although not shown in the drawings, one or more adhesive layers may be provided between any of the layers  110 ,  120 ,  130 ,  140 , and  150 .  
      An outer covering or sheath  160  is then at least partially disposed or otherwise formed over the outer tensile layer  150 . The sheath  160  is fabricated from the TPV described herein. The TPV sheath  160  provides low temperature flexibility, improved thermal insulation characteristics, lighter weight and resistance to degradation. The TPV sheath  160  also has a very good resistance to chemical elements and fatigue when in contact with drilling fluids and seawater. Moreover, the TPV sheath  160  exhibits good fatigue properties, low environmental stress-cracking resistance, and good temperature resistance. More importantly, the TPV sheath  160  is capable of having a cross sectional thickness greater than 5 mm, such as greater than 6 mm, greater than 10 mm, and greater than 16 mm, because of the enhanced cooling afforded by the one or more nucleating agents.  
      As mentioned above, it is believed that the addition of the one or more nucleating agents provides a plurality of nucleating sites for the polypropylene component to crystallize. As such, a greater amount of smaller crystals are formed in contrast to fewer, larger crystals that form without the addition of the nucleating agents described herein. As a result, the smaller crystals require less cooling time, thereby setting the entire cross section of the TPV material as opposed to just the outer portions.  
     EXAMPLES  
      The following examples illustrate the reduced cooling times of extruded TPV samples. As seen below, faster cooling times have been observed even in samples having a thickness of greater than 5 mm without a sacrifice in performance or strength of the TPV materials.  
      For purposes of convenience, various specific test procedures are identified for determining properties such as elongation break, peak stress, break strain, modulus, Shore A Hardness and Shore D Hardness. However, when a person of ordinary skill reads this patent and wishes to determine whether a composition or polymer has a particular property identified in a claim, then any published or well-recognized method or test procedure can be followed to determine that property, although the specifically identified procedure is preferred. Each claim should be construed to cover the results of any of such procedures, even to the extent different procedures may yield different results or measurements. Thus, a person of ordinary skill in the art is to expect experimental variations in measured properties that are reflected in the claims. All numerical values can be considered to be “about” or “approximately” the stated value, in view of the nature of testing in general.  
      Comparative Samples 1-5 (CS 1-5) are compositions of a TPV with no nucleating agent. Comparative Samples 1-5 were extruded samples of Santoprene® 203-50 (Advanced Elastomer Systems, L.P.) and polypropylene in the weight percentages shown in Table 1.  
      Samples 1-6 (S1-6) are compositions of a TPV blended with one or more nucleating agents as described. Samples 1-6 were extruded samples of Santoprene® 203-50 (Advanced Elastomer Systems, L.P.), polypropylene, and the one or more nucleating agents in the weight percentages shown in Table 1.  
      Each extruded strip was 46 mm wide and 2 mm thick, and was extruded on a MAPRE 38 mm single-screw extruder. The extruded strip of Comparative Sample 1 (CS-1) was cooled at rapid cooling conditions using tap-water. The extruded strip of Comparative Sample 2 (CS-2) was cooled at slower cooling conditions with air. The extruded strips of Comparative Samples 3-5 (CS 3-5) were cooled in a drying oven at 120° C. for 10 minutes, 20 minutes, or 30 minutes, as recited in Table 1. Each of the extruded strips of Samples 1-6 (S 1-6) were cooled in a drying oven at 120° C. for 20 minutes. The drying oven was placed in close proximity to the extrusion line to prevent a premature cooling of the extruded strip samples.  
      The tensile properties were evaluated using method TPE 0153, on a dumbbell ISO type 1, at 50 mm/min speed. The reported result is a median value of 5 measurements each taken at room temperature. As shown in Table 1, the mechanical characteristics of Comparative Samples 1-5 (CS 1-5) substantially decreased after an aging of 10, 20 and 30 minutes in the oven at 120° C. Conversely, the use of nucleating agents showed a positive effect in comparison with the decreased properties observed for the Comparative Samples. Particularly, Samples 1-3 and 5-6 each exhibited at least a 10% increase in Peak Stress, more than twice the Break Strain, and a roughly a 10% increase in 100% Modulus compared to the Comparative Sample 4 which was also cooled in the oven for 20 minutes at 120° C. Furthermore, Samples 1-6 showed the most favorable results compared to TPV samples (Comparative Sample 1) cooled with the more desirable, timely method of water cooling.  
                                                   TABLE 1                                                       TENSILE   ULTIMATE   100%               POLY-   IRGASTAB   HPN   COOLING   STRENGTH   ELONGATION   MODULUS           TPV   PROPYLENE   NA 11   68L   CONDITIONS   (MPa)   (%)   (MPa)                                                                        Comparative 1   95   5   —   —   Water   24.27   623   12.93       Comparative 2   95   5   —   —   Air   16.29   383   13.28       Comparative 3   95   5   —   —   10 min @ 120° C.   10.91   55   12.08       Comparative 4   95   5   —   —   20 min @ 120° C.   11.75   74   11.96       Comparative 5   95   5   —   —   30 min @ 120° C.   10.86   57   —       Sample 1   94.9   5   0.1   —   20 min @ 120° C.   13.6   162   12.87       Sample 2   94.8   5   0.2   —   20 min @ 120° C.   13.21   140   12.85       Sample 3   94.5   5   0.5   1   20 min @ 120° C.   14.06   206   12.7       Sample 4   94.9   5   —   0.1   20 min @ 120° C.   11.64   91   —       Sample 5   94.8   5   —   0.2   20 min @ 120° C.   13.33   175   12.34       Sample 6   94.5   5       0.5   20 min @ 120° C.   12.46   171   11.63