Thermoelastic composition of ethylene-hexene or ethylene-butene copolymer and rubber

Abstract: Thermoplastic compositions are prepared by blending an ethylene-hexene and/or an ethylene-butene copolymer resin, with rubber and dynamically vulcanizing the rubber to form a heat-shrinkable dynamically vulcanized alloy to exceptionally low hardness, and great flexibility and elasticity. The preferred rubber is halogenated butyl rubber. Uncured rubber can be included in the composition.

Description: Background of the Invention 1. Field of the Invention This invention relates to thermoplastic elastomeric compositions which, while having the reprocessibility of thermoplastic resins, are yet heat shrinkable, elastomeric in nature, and of low hardness. The result of this invention is accomplished by blending in or as a thermoplastic resin a plastomeric ethylene copolymer resin with a rubber and vulcanizing the rubber by dynamic vulcanization techniques. 2. Background Polymer blends which have a combination of both elastic and thermoplastic properties are of significant commercial interest. Such thermoelastic compositions are generally obtained by blending an elastomeric polymer with a thermoplastic resin in a way such that the elastomer is intimately and uniformly dispersed as a discrete phase within a continuous phase of the thermoplastic resin. These polymer blends have been given the generic designation of Thermoplastic Olefins ("TPO"). They exhibit some of the properties of a cured elastomer as well as the reprocessibility of a thermoplastic resin. The elastomeric characteristics are enhanced if one component of the blend is a vulcanizable elastomer which is wholly or partially cross-linked. The earliest work in the curing of a TPO composition was by Gessler and Haslett; see U.S. Patent No. 3,037,954. That patent teaches the concept of "dynamic curing" wherein a vulcanizable elastomer is dispersed into a resinous thermoplastic polymer and the elastomer cured while continuously mixing and shearing the polymer blend. The blend resulting is a micro-gel dispersion of cured elastomer in an uncured matrix of resinous thermoplastic polymer. Gessler, '954 discloses compositions comprising polypropylene and a rubber such as, inter alia, butyl rubber; chlorinated butyl rubber, polybutadiene, polychloroprene and polyisobutene. Compositions of 50 to 95 parts polypropylene and 5 to 50 parts of rubber are disclosed. U.S. Patent Nos. 3,758,643 and 3,806,558 disclose TPO type polymer blends comprising an olefin thermoplastic resin and and olefin copolymer rubber wherein the rubber is dynamically cured to a partial cure state. The compositions are reprocessible and result in molded products having good surface appearance. However, the potential applications of such blends are limited by their high compression set and/or low softening temperature resulting from only a partial cure of the rubber. Furthermore, the partial peroxide cure utilized in such blends is difficult to control from the standpoint of completeness of reaction, resulting in batch to batch variations in product properties. U.S. Patent No. 4,104,210 discloses TPO blends which comprise 25 to 45 parts of a polyolefin resin and from 55 to 75 parts of a diene rubber which is a homopolymer or copolymer of a diolefin. U.S. Patent No. 4,130,534 discloses TPO blends which comprise up to 60 wt% of a polyolefin resin and 40 wt% or more of a butyl rubber. The butyl rubbers utilized include butyl rubber per se as well as chlorinated or brominated butyl rubber. In each of the TPO blends described by the '210 and '534 patents the rubber component is said to be fully cured, the cure being a dynamic vulcanization. The preferred polyolefin thermoplastic phase for each is stated to be polyethylene or polypropylene, with polypropylene the most preferred. TPO systems wherein the rubber is fully cured have the disadvantage that, as a result of poor flow characteristics, injection molded components made from such TPO's exhibit "flow line" imperfections. As a consequence, special mold designs are required to minimize the problem, especially for large parts. Applications are further limited because of the high Shore A hardness of such compositions. U.S. Patent No. 3,081,279 discloses compositions wherein a rubber, such as butyl rubber, is combined with a sulfochlorinated polyolefin resin and cured. The uncured blend is said to have improved processing characteristics. U.S. Patent No. 2,369,471 discloses blends of ethylene polymers with various hydrocarbon rubbers and halogenated rubbers. The compositions are either uncured or compression molded vulcanizates. U.S. Patent No. 3,326,833 discloses compositions of a copolymer of ethylene with an alkyl ester of an alpha-beta-monethylenically unsaturated monocarboxylic acid, e.g., ethylene-ethylacrylate copolymer, and a halogenated olefin polymer. The rubber can be halogenated butyl rubber or chlorinated polyethylene. The compositions when uncured are thermoplastic and when peroxide cross-linked form insoluble non-thermoplastic resins. U.S. Patent No. 4,639,487 discloses a TPO blend which utilizes as the thermoplastic continuous phase an ethylene vinyl ester or ethylene-alkylacrylate copolymer with a rubber component which may be a butyl rubber, halogenated butyl rubber, polyisoprene, polychloroprene, styrene-butadiene rubber, nitrile rubber, chlorosulfonated polyethylene, wherein the rubber component is dynamically vulcanized to disperse the rubber as fully cured fine particles of a "micro-gel" within the thermo-plastic matrix. Such TPO compositions possess exceptional resiliency, high coefficient of friction surfaces and low compression set. Although the TPO blends as disclosed by U.S. Patent No. 4,639,487 have improved properties compared to prior types of TPO blends, it is still desirable to develop a TPO of even further improved properties, as with respect to lower hardness and increased flexibility at comparable degrees of elasticity and, particularly, with respect to improved high temperature processing stability. The TPO compositions of U.S. Patent No. 4,639,487 wherein the vinyl ester content of the thermoplastic component exceeds about 20 wt% tend to become cured or thermoset upon prolonged exposures to injection processing temperatures. EP-A-0190497 relates to a composition of olefin resin (polypropylene or HDPE) and dynamically vulcanized halobutyl rubber and polychloroprene rubber. Even if this composition has good processability and flow characteristics, it is not enough soft and flexible to meet the purposes of the present invention. Summary of the Invention A low hardness heat shrinkable, reprocessible TPO can be prepared by utilizing as or in the thermoplastic resin a plastomeric ethylene copolymer, such as ethylene-hexene and ethylene-butene, and fully curing the rubber component of the TPO by dynamic vulcanization. The subject matter of the present invention is a thermoplastic elastomeric composition, characterized in that it comprises (a) a thermoplastic resin containing at least 25 wt %, based upon the weight of the thermoplastic resin, of a plastomeric copolymer selected from the group consisting of ethylene-hexene copolymer, ethylene-butene copolymer and mixtures thereof, said hexene or butene content of the respective copolymers being at least 20 wt % and said plastomeric copolymer having a density of less than 0.900 and a degree of crystallinity measured as a heat of fusion from 5 to 85 J/g, and (b) a rubber selected from the group consisting of butyl rubber, halogenated butyl rubber, ethylene-propylene-diene rubber (EPDM), polyisoprene, polychloroprene, styrene-butadiene rubber, nitrile rubber, chlorosulfonated polyethylene and mixtures thereof, said rubber having been non-peroxide vulcanized to a fully cured state in the presence of said plastomeric copolymer. Another subject matter of the present invention is a process for preparing a dynamically vulcanized composition comprising a thermoplastic resin and a fully vulcanized rubber, characterized in that is comprises the steps of : (a) blending a thermoplastic resin comprising a plastomeric copolymer selected from the group consisting of ethylene-hexene copolymer, ethylene-butene copolymer and mixtures thereof, said hexene or butene content of the respective copolymers being at least 20 wt %, said plastomeric copolymer having a density of less than 0.900 and a degree of crystallinity measured as a heat of fusion of from 5 to 85 J/g and a rubber at a temperature above the melting point of said resin to produce a blend, said rubber being selected from the group consisting of butyl rubber, halogenated butyl rubber, ethylene-propylene-diene rubber (EPDM), polyisoprene, polychloroprene, styrene-butadiene rubber, nitrile rubber, chlorosulfonated polyethylene, and mixtures thereof; (b) adding a non-peroxide cure system effective for vulcanizing only said rubber in said blend; and (c) vulcanizing said rubber under dynamic vulcanization conditions for a time sufficient to vulcanize fully said rubber and produce a dynamically vulcanized blend. Particular embodiments of the present invention are disclosed in claims 2 to 15 and 17 to 21. The preferred plastomeric ethylene copolymers which may be utilized in or as the thermoplastic resin are those ethylene-hexene and ethylene-butene copolymers having a melt index (MI) of from 0.3 to 50 and a density of 0.870 to less than 0.900. The preferred rubber component of the invention TPO is halogenated butyl rubber. TPO compositions in accordance with the invention possess exceptionally low hardness, flexibility and elasticity. Further, such TPO compositions are completely rheologically stable at the elevated temperatures that are typically employed in processing such compositions by injection, extrusion or compression molding into finished articles. Detailed Description As used in the specification and claims, the term "dynamic vulcanization" means a vulcanization process for a rubber containing TPO composition wherein the rubber is vulcanized under conditions of high shear, as a result of which, the rubber is simultaneously cross-linked and dispersed as fine particles of a "micro-gel" within the thermoplastic resin matrix. Dynamic vulcanization is effected by mixing the TPO ingredients at a temperature which is at or above the curing temperature of the rubber in equipment such as roll mills, Banbury mixers, continuous mixers, kneaders or mixing extruders, e.g., twin screw extruders. The unique characteristic of the dynamically cured compositions is that, notwithstanding the fact that the rubber component is fully cured, the compositions can be processed and reprocessed by conventional rubber processing techniques such as extrusion, injection molding, compression molding. Scrap or flashing can be salvaged and reprocessed. The term "dynamically vulcanized alloy" (DVA) as used in the specification and claims means a composition comprising a thermoplastic resin containing a ethylene-hexene copolymer and a rubber wherein at least a part of the rubber has been dynamically vulcanized to a fully cured state. The DVA compositions are prepared by blending together the ethylene-hexene copolymer containing thermoplastic resin and rubber with curatives and fillers under conditions of dynamic vulcanization. In preparing the heat shrinkable DVA compositions of this invention, the plastomeric ethylene copolymer containing thermoplastic resin is blended with at least one rubber and the rubber is vulcanized by dynamic vulcanization. While blends of polyolefin thermoplastic resins may be utilized in the practice of this invention, the polyolefin thermoplastic resin is or contains a copolymer of ethylene with hexene or butene. The DVA composition of this invention must include a plastomeric ethylene copolymer within the polyolefin thermoplastic resin from which the DVA is prepared. Polyolefin resins which can optionally be included in the compositions of this invention include polybutylene, LDPE and LLDPE as well as copolymers of ethylene with unsaturated esters of lower carboxylic acids. The term "polybutylene" generally refers to thermoplastic resins of both poly(1-butene)homopolymer and the copolymer with, for example, ethylene, propylene, pentene-1. Polybutylene is manufactured via a stereo-specific Ziegler-Natta polymerization of monomer(s). Commercially useful products are of high molecular weight and isotacticity. A variety of commercial grades of both homopolymer and ethylene copolymer are available with melt indices that range from 0.3 to 20 g/10 min. The term "low density polyethylene" or "LDPE" as used in the specification and claims mean both low and medium density polyethylene having densities of 0.910 to 0.940 g/cc. The terms include linear polyethylene as well as copolymers of ethylene which are thermoplastic resins. Linear low density polyethylene (LLDPE) is a class of low density polyethylene characterized by little, if any, long chain branching, in contrast to conventional LDPE. The processes for producing LLDPE are well known in the art and commercial grades of this polyolefin resin are available. Generally, it is produced in gas-phase fluidized bed reactors or liquid-phase solution process reactors; the former process can be carried out at pressures of 689 to 2,068 KPa (100 to 300 psi) and temperatures as low as 100°C. The term "plastomeric ethylene copolymer" as used herein includes both plastomeric ethylene-hexene copolymers and ethylene-butene copolymers. The terms "ethylene-hexene copolymer" and "ethylene-butene copolymer" resin as used herein mean a copolymer of ethylene with 1-hexene or 1-butene respectively wherein the hexene or butene content of the respective copolymers is from 20 wt.% to 50 wt.% preferably from 20 to 45, and most preferably from 20 to 40 wt%. The ethylene-hexene or ethylene-butene copolymers suitable for use in the practice of this invention have a melt index (MI) measured by ASTM Standard D1238 Condition E of from 0.3 to 50 and preferably from 0.5 to 10. The ethylene-hexene or ethylene-butene copolymer has a degree of crystallinity measured as a heat of fusion by DSC of from 5 to 85 J/g. The preferred ethylene-hexene or ethylene-butene copolymers have a density of from 0.870 to less than 0.900. For greatest elasticity or flexibility, the ethylene-hexene or ethylene-butene copolymer has a density of less than to 0.900 and a minimum comonomer content of 20 wt%. Both the ethylene-hexene or ethylene-butene copolymers required for use in the practice of this invention are commercially available in a variety of different grades. The curable rubbers used in the practice of this invention are butyl rubber, halogenated butyl rubber, ethylene-propylene-diene rubber (EPDM), polyisoprene, polychloroprene, styrene-butadiene rubber, nitrile rubbers, chlorosulfonated polyethylene and mixtures thereof. Since the plastomeric ethylene copolymer will peroxide cure and therefore lose its thermoplastic properties, rubbers such as ethylene-propylene copolymers (EPM) which require a peroxide cure should not be used as the curable rubber component in the practice of this invention. The terms EPM and EPDM are used in the sense of their ASTM designations. EPM is an ethylene-propylene copolymer rubber which can be cross-linked by radiation curing or peroxide curing. EPDM is a terpolymer of ethylene, propylene and a non-conjugated diene. Examples of suitable non-conjugated dienes are 5-ethylidene-2-norbornene (ENB); 1,4-hexadiene; 5-methylene-2-norbornene (MNB); 1,6-octadiene; 5-methyl-1,4-hexadiene; 3,7-dimethyl-1,6-octadiene; 1,3-cyclopentadiene; 1,4-cyclohexadiene; tetrahydroindene; methyltetrahydroindene; dicyclopentadiene; 5-isopropylidene-2-norbornene; 5-vinyl-norbornene. The term "nitrile rubber" means an acrylonitrile copolymer rubber. Suitable nitrile rubbers comprise rubbery polymers of 1,3-butadiene or isoprene and acrylonitrile. Preferred nitrile rubbers comprise polymers of 1,3-butadiene and 20-50 wt% acrylonitrile. Any nitrile rubber which is a "solid" rubber having an average molecular weight of at least 50,000, and preferably between 100,000-1,000,000 can be used. Commercially available nitrile rubbers suitable for the practice of the invention are described in Rubber World Blue Book , 1980 Edition, Materials and Compounding Ingredients for Rubber, pages 386-406. Butyl rubber is a copolymer of an isoolefin and a conjugated multiolefin. The useful rubber copolymers comprise a major portion of isoolefin and a minor amount, preferably not more than 30 wt%, of a conjugated multiolefin. The preferred rubber copolymers comprise 85-99.5 wt% (preferably 95-99.5 wt%) of a C₄-C₋₇ isoolefin, such as isobutylene, and 15-0.5 wt% (preferably 5 - 0.5 wt%) of a multiolefin of 4-14 carbon atoms. These copolymers are referred to in the literature as "butyl rubber"; see for example, the textbook Synthetic Rubber by G. S. Whitby (1954 edition by John Wiley and Sons, Inc.), pages 838-891. The term "butyl rubber" as used in the specification and claims includes the aforementioned copolymers of an isoolefin having 4-7 carbon atoms and 0.5 to 20 wt% of a conjugated multiolefin of 4-10 carbon atoms. Preferably these copolymers contain 0.5 to 5% conjugated multiolefin. The preferred isoolefin is isobutylene. Suitable conjugated multiolefins include isoprene, butadiene, dimethyl butadiene, piperylene. Commercial butyl rubber is a copolymer of isobutylene and minor amounts of isoprene. Butyl rubber as above described may be halogenated with from 0.1 to 10, preferably, 0.5 to 3.0 wt% chlorine or bromine. The chlorinated species of butyl rubber is commonly referred to as chlorinated butyl rubber. The plastomeric ethylene copolymer resin component used in the practice of this invention comprises about 25 to 100 wt% of the thermoplastic resin component of the blend; preferably the ethylene copolymer resin component comprises 35 to 100 wt% thermoplastic resin; more preferably 45 to 100 wt%. In its most preferred embodiment, the thermoplastic resin of the DVA of this invention consists solely of the plastomeric ethylene copolymer. When the LDPE, LLDPE or polybutylene, which may optionally be included in the thermoplastic resin component of the composition, is utilized it comprises 0 to 75 wt% of the thermoplastic resin component; preferably 0 to 65 wt%; more preferably 0 to 55 wt%. The thermoplastic resin is blended with at least one rubber and the rubber component of the blend is vulcanized using dynamic vulcanization techniques. The thermoplastic resin comprises 20 to 90 wt% based on the resin plus rubber in the DVA; preferably 30 to 80 wt%; more preferably 40 to 60 wt%. The rubber component of the DVA compositions comprises 80 to 10 wt% of the composition, based on resin plus rubber; preferably 70 to 20 wt%; more preferably 60 to 40 wt% rubber, based on the resin plus rubber component of the blend. Where it is desired to prepare a DVA for use in blown film with good heat shrink properties, the curable rubber preferably comprises 10 to 40 wt% of the total composition, i.e., resin, plus rubber and additives; preferably at least 12 wt%; more preferably at least 15 wt%. In addition to its polymer component, the DVA composition of this invention can include reinforcing and non-reinforcing fillers, antioxidants, stabilizers, rubber processing oils, lubricants (e.g., oleamide), antiblocking agents, antistatic agents, waxes, coupling agents for the fillers, foaming agents, pigments, flame retardants, and other processing aids known to the rubber compounding art. The pigments and fillers can comprise up to 50 wt% of the total DVA composition based on polymer component plus additives; preferably pigments and fillers comprise 0 to 30 wt% of the total composition. Fillers can be inorganic fillers such as calcium carbonate, clays, silicas, talc, titanium dioxide or carbon black. Any type of carbon black can be used, such as channel blacks, furnace blacks, thermal blacks, acetylene black and lamp black. Rubber process oils have particular ASTM designations depending on whether they fall into the class of paraffinic, naphthenic or aromatic process oils. They are derived from petroleum fractions. The type of process oil utilized will be that customarily used in conjunction with the rubber component. The ordinarily skilled rubber chemist will recognize which type of oil should be utilized with a particular rubber. The quantity of rubber process oil utilized is based on the total rubber content, both cured and uncured, and can be defined as the ratio, by weight, of process oil to the total rubber in the DVA. This ratio can vary from 0 to 1.5/1; preferably 0.2/1 to 1.00/1; more preferably 0.3/1 to 0.8/1. Larger amounts of process oil can be used, the deficit being reduced physical strength of the composition. Oils other than petroleum based oils, such as oils derived from coal tar and pine tar, can also be utilized. In addition to the petroleum derived rubber process oils, organic esters and other synthetic plasticizers can be used. Antioxidants can be utilized in the composition of this invention - the particular antioxidant utilized will depend on the rubbers utilized and more than one type may be required. Their proper selection is well within the ordinary skill of the rubber processing chemist. Antioxidants will generally fall into the class of chemical protectors or physical protectants. Physical protectants are used where there is to be little movement in the part to be manufactured from the composition. These are generally waxy materials which impart a "bloom" to the surface of the rubber part and form a protective coating to shield the part from oxygen, ozone. The chemical protectors generally fall into three chemical groups; secondary amines, phenolics and phosphites. Examples of types of antioxidants useful in the practice of this invention are hindered phenols, amino phenols, hydroquinones, alkyldiamines, amine condensation products. Examples of these and other types of antioxidants are styrenated phenol; 2,2′-methylene-bis(4-methyl-6-1, butylphenol); 2,6′-di-t-butyl-o-dimethylamino-p-cresol; hydroquinone monobenzyl ether; octylated diphenyl amine; phenyl-beta-naphthylamine; N,N′-diphenylethylene diamine; aldol-alpha-naphthylamine; N,N′-diphenyl-p-phenylene diamine. The physical antioxidants include mixed petroleum waxes and microcrystalline waxes. Any conventional cure system for the rubber to be dynamically vulcanized can be used except that peroxide cures are specifically excluded from the practice of this invention. Under conditions which would result in a fully cured rubber using peroxide, the plastomeric ethylene copolymer in the thermoplastic resin would vulcanize, thereby resulting in a fully cured non-thermoplastic composition. Otherwise, any particular curatives known in the art for the vulcanization of rubbers are suitable for the blends incorporating the plastomeric ethylene copolymer. These include sulfur cures as well as non-sulfur cures. For example, halogenated butyl rubber can be cured using zinc oxide. Of course, accelerators such as dithiocarbamates or thiurams and thioureas can be included in these zinc oxide cures. Zinc oxide free cures of halogenated butyl rubber known to the art can also be utilized. For example, such vulcanizing systems comprise litharge, 2-mer-captoimidazoline and diphenyl guanidine. Resin cures can be used for both butyl rubber, halogenated butyl rubber and the EPDM rubbers. The resins useful as curatives are phenolic resins, brominated phenolic resins, urethane resins. The halogenated resin cure systems are generally metal activated where the rubber is an EPDM. While phenolic resin cures are suitable cures, they impart a yellowish or orangish tinge to the rubber part. For halogenated butyl rubber, a preferred cure is one based on ZnO and/or MgO. Such cures permit the use of pigments such as TiO₂ to give bright white compositions. In this system, the MgO acts not as an accelerator but as an acid acceptor to stabilize the rubber from dehydrohalogenation. Illustrative of accelerators which can be used in conjunction with ZnO for curing halobutyl rubber are 2,6-di-tert-butyl-para-cresol; N,N′-diethylthiourea; di-ortho-tolylguanidine; dipentamethylene thuiram tetrasulfide; ethylene trithiocarbonate; 2-mercaptobenzothiazole; benzothiazole disulfide; N-phenyl-betanaphthylamine; tetramethyl thuiram disulfide, zinc diethyldithiocarbamate, zinc dibutyldithiocarbamate, and zinc dimethyldithiocarbamate. Formulations for the ZnO cure of halobutyl rubber are well known in the art. A preferred cure system comprises ZnO and m-phenylene bismaleimide since this system results in a vulcanized rubber with low compression set. It is within the scope of this invention to incorporate an uncured rubber in the composition. In most circumstances, this can be accomplished by selecting as the uncured rubber a rubber which cannot be vulcanized by the vulcanizing agent used to cure the rubber which is to be dynamically vulcanized. For example, where the rubber to be cured is a halogenated rubber and the cure system comprises ZnO, any other rubber which requires sulfur or another curative to vulcanize it or is not vulcanizable can be included. Such rubbers include EPM, EPDM, polyisobutylene, natural rubber. Another means of incorporating the uncured rubber is by utilizing halobutyl rubber as the dynamically vulcanized rubber and butyl rubber as the uncured rubber, where the cure system is ineffective to cure the butyl rubber, e.g. zinc oxide. In another embodiment the DVA can first be prepared from the resin and the rubber by dynamic vulcanization and after vulcanization a second uncured rubber can be blended into the DVA at a temperature above the melting point of the thermoplastic resin. In another embodiment of this invention, two rubbers are blended together and one of them is dynamically vulcanized using a cure system which is not effective for the other rubber, thereby forming a composition comprising a fully vulcanized rubber dispersed within the unvulcanized rubber. This composition can then be let down into the plastomeric ethylene copolymer resin to form the composition of this invention. In a variant of this invention, a first rubber is dynamically vulcanized while in intimate contact with a plastomeric ethylene copolymer utilizing an excess of vulcanizing agent to form the DVA of this invention. Thereafter, additional rubber is added and dynamically vulcanized, the quantity of curative having been preselected to ensure that it is inadequate to fully vulcanize the additional rubber. In another embodiment of this invention the DVA is prepared using a plastomeric ethylene copolymer and one rubber. Subsequently, under conditions of dynamic vulcanization a second rubber is added to the DVA with only sufficient curative to partially cure the second rubber. For example, ethylene copolymer and an EPDM are blended and a sulfur curative added. The EPDM is dynamically vulcanized to form the DVA of this invention. Subsequently, chlorobutyl rubber is added with just sufficient ZnO to only partially cure the chlorinated butyl rubber. Where an uncured rubber is included in the DVA composition of this invention, it comprises 0 to 25 wt% of the total rubber in the composition, preferably 5 to 20 wt%. While any combination of rubbers may be utilized, the preferred rubbers are halogenated rubber which can be ZnO cured; e.g., halogenated butyl rubber and polychloroprene. These rubbers when ZnO cured result in products which have a low odor and have broad FDA compliance in uses such as pharmaceutical enclosures, I.V. solution bag port caps, stoppers, syringes, jar seals, food storage bins. In a preferred embodiment, the rubber to be vulcanized is chlorinated or brominated butyl rubber. Such halogenated butyl rubbers are preferably vulcanized with zinc oxide cures. Sulfur-bearing accelerators can be utilized with the zinc oxide. This accelerator will generally not vulcanize sulfur curable rubbers such as EPDM when used at the low levels necessary to cure a halogenated butyl rubber. Illustrative of accelerators which can be used in conjunction with ZnO for curing halobutyl rubber are 2,6-di-tert-butyl-para-cresol; N,N′-diethylthiourea; di-ortho-tolylguanidine; dipentamethylene thuiram tetrasulfide; ethylene trithiocarbamate; 2-mercaptobenzothiazole; benzothiazole disulfide; N-phenyl-betanaphthylamine; tetramethyl thuiram disulfide, zinc diethyldithiocarbamate, zinc dibutyldithiocarbamate, and zinc dimethyldithiocarbamate. Formulations for the ZnO cure of halobutyl rubber are well known in the art. A preferred cure system comprises MgO, ZnO and zinc diethyl-dithiocarbamate since this system results in a vulcanized rubber with low compression set. In the practice of this invention a thermoplastic resin comprising or containing the plastomeric ethylene copolymer is mixed with a rubber at a temperature sufficient to soften the resin or, more commonly, at a temperature above its melting point where the resin is crystalline at room temperature. After the resin and rubbers are intimately mixed, the curative is added. Heating and masticating at vulcanization temperatures are generally adequate to complete vulcanization in 0.5 to 10 minutes. The vulcanization time can be reduced by elevating the temperature of vulcanization. A suitable range of vulcanization temperatures is from about the peak melting point of the resin (35 to 125°C in the case of ethylene-hexene or ethylene-butene copolymer) to 250°C; more typically, the temperature range is 150°C to 225°C. Preferably the vulcanization is carried out at a temperature of 160°C to 200°C. It is preferred that the mixing process be continued until vulcanization is complete. If vulcanization is permitted to continue after mixing has stopped, the composition will not be reprocessible as a thermoplastic. However, the dynamic vulcanization can be carried out in stages. For example, vulcanization can be commenced at high temperatures in a twin screw extruder and before vulcanization is complete pellets can be formed of the partially prepared DVA using an underwater pelletizer, thereby quenching the curing step. At a later time vulcanization can be completed under dynamic vulcanization conditions. Those ordinarily skilled in the art will appreciate the appropriate quantities, types of curatives and extent of mixing time required to carry out the vulcanization of the rubber. Where necessary the rubber can be vulcanized using varying amounts of curative to determine the optimum cure system to be utilized and the appropriate cure conditions to obtain a full cure. While it is preferred that all components be present in the mix prior to carrying out the dynamic vulcanization process of this invention, this is not a necessary condition. For example, only the rubbers need be mixed thoroughly, followed by dynamic vulcanization in the absence of thermoplastic resin. After vulcanization is complete, the dynamically vulcanized blend of rubbers can be let down into a plastomeric ethylene copolymer resin to prepare the compositions of this invention. The term "fully vulcanized" as used in the specifications and claims with respect to the dynamically vulcanized rubber component of this invention means that the rubber component to be vulcanized has been cured to a state in which the physical properties of the rubber are developed to impart elastomeric properties to the rubber generally associated with the rubber in its conventional vulcanized state. The degree of cure of the vulcanized rubber can be described in terms of gel content or conversely extractable components. Alternatively, the degree of cure can be expressed in terms of cross-link density. Where the determination of extractable is an appropriate measure of the state of cure, the improved thermoplastic elastomeric compositions are produced by vulcanizing the curable rubber component of the blends to the extent that the composition contains no more than about four percent by weight of the cured rubber component extractable at room temperature by a solvent which dissolves the rubber which is intended to be vulcanized, and preferably to the extent that the composition contains less than two percent by weight extractable. In general, the less extractables of the cured rubber component, the better are the properties and still more preferable are compositions comprising essentially no extractable rubber from the cured rubber phase (less than 0.5 wt%). Gel content reported as percent gel is determined by a procedure which comprises determining the amount of insoluble polymer by soaking the specimen for 48 hours in organic solvent at room temperature and weighing the dried residue and making suitable corrections based upon knowledge of the composition. Thus, corrected initial and final weights are obtained by subtracting from the initial weight, the weight of 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 DVA which it is not intended to cure. Any insoluble pigments, fillers, are subtracted from both the initial and final weights. To employ cross-link density as the measure of the state of cure which characterizes the improved thermoplastic elastomeric compositions, the blends are vulcanized to the extent which corresponds to vulcanizing the same rubber as in the blend statically cured under pressure in a mold with such amounts of the same curatives as in the blend and under such conditions of time and temperature to give an effective cross-link density greater than about 3 x 10⁻⁵ moles per milliliter of rubber and preferably greater than about 5 x 10⁻⁵ or even more preferably 1 x 10⁻⁴ moles per milliliter of rubber. The blend is then dynamically vulcanized under similar conditions with the same amount of curative based on the rubber content of the blend as was required for the rubber alone. The cross-link density so determined may be regarded as a measure of the amount of vulcanization which gives the improved thermoplastics. However, it should not be assumed, from the fact that the amount of curative is based on the rubber content of the blend and is that amount which gives the rubber alone the aforesaid cross-link density, that the curative does not react with the resin or that there is no reaction between the resin and rubber. There may be highly significant reactions involved but of limited extent. However, the assumption that the cross-link density determined as described provides a useful approximation of the cross-link density of the thermoplastic elastomeric compositions is consistent with the thermoplastic properties and with the fact that the large proportion of the resin can be removed from the composition by high temperature solvent extraction, for example, by boiling decalin extraction. The cross-link density of the rubber is determined by equilibrium solvent swelling using the Flory-Rehner equation. J. Rubber Chem. and Tech. 30, p. 929. The appropriate Huggins solubility parameters for rubber-solvent pairs used in the calculation were obtained from the review article by Sheehan and Bisio, J. Rubber Chem. & Tech. , 39, 149. If the extracted gel content of the vulcanized rubber is low, it is necessary to use the correction of Bueche wherein the term "v" is multiplied by the gel fraction (% gel/100). The cross-link density is half the effective network chain density "v" determined in the absence of resin. The cross-link density of the vulcanized blends should therefore be understood to refer to the value determined on the same rubber as in the blend in the manner described. Still more preferred compositions meet both of the aforedescribed measures of state of cure, namely, by estimation of cross-link density and percent of rubber extractable. In the practice of this invention resins such as LDPE, LLDPE and polybutylene can be utilized in conjunction with the ethylene copolymer resin. Generally, any resin with a crystalline melting point of less than 126°C can be used in conjunction with the ethylene copolymer resin. In order to produce a heat shrink composition from the DVA composition of this invention, the DVA compositions are prepared in accordance with procedures well-known in the art. The DVA composition is oriented at a temperature slightly below the softening point of the thermoplastic resin and "frozen" into the oriented configuration, i.e., film, tubing, tape. The forming of a product and its orientation can be continuous, e.g., blown film, or can be accomplished in a separate operation. Upon subsequent heating to a temperature above the softening point of the thermoplastic resin, the composition will shrink. The advantages of the instant invention will be more readily appreciated by reference to the following examples. Ingredients used in making compositions as reported in the examples are identified in Table 1. EXAMPLES 1 - 10 Comparative and inventive compositions as described in Table 2 were mixed in a 1.36 kg (3 lb.) Banbury mixer using a 7 to 8.5 minute cycle. The blend compositions were dynamically vulcanised in the mixer by prolonging the mix for 3.5 minutes at an elevated temperature of 204 to 221°C (400 to 430°F) after the addition of the cure system. The compositions containing ethylene-hexene, Examples 2, 4, 6, 8, and 10, were more viscous than the comparative blend compositions and this produced a faster temperature rise and correspondingly shorter cycle for dynamic vulcanization. After completion of dynamic vulcanization each blend was sheeted out on a cool mill and then ground for feed to a 15-ton Boy injection molding machine. Dumbbells were injection molded from each blend and compared in properties. The properties measured for each are reported in Table 3. The test procedures employed in making the property measurements are identified in Table 4. Examples utilizing ethylene-butene in place of ethylene-hexene are prepared as exemplified. EXAMPLE NO. 1 2 3 4 5 6 7 8 9 10 EVA (LD 722.62; 20% VA) 27 --- 18 --- --- --- --- --- --- --- EVA (XR-70.36; 28% VA) --- --- --- --- 40 --- 18.5 --- --- --- Gulf EMA (20% MA) --- --- --- --- --- --- --- --- 18.5 --- Chlorobutyl 1066 27 27 36 36 35 35 18.5 18.5 18.5 18.5 Neoprene W --- --- --- --- --- --- 18.5 18.5 18.5 18.5 Ethylene-Hexene (30% 1-Hexene) --- 27 --- 18 --- 40 --- 18.5 --- 18.5 Circosol 4240 Oil 20 20 20 20 15 15 15 15 29 29 Atomite 19 19 19 19 6 6 22.5 22.5 8.4 8.4 Maglite D 1.8 1.8 1.8 1.8 0.5 0.5 1.8 1.8 1.8 1.8 Irganox B-215 0.2 0.2 0.2 0.2 --- --- --- --- --- --- Irganox 1010 --- --- --- --- 0.2 0.2 0.2 0.2 0.1 0.1 Stearic Acid 0.5 0.5 0.5 0.5 --- --- 0.5 0.5 0.5 0.5 DLTDP --- --- --- --- --- --- --- --- 0.1 0.1 Protox 169 Zinc Oxide 3.6 3.6 3.6 3.6 2.5 2.5 3.6 3.6 3.6 3.6 Permalux 0.9 0.9 0.9 0.9 --- --- 0.9 0.9 0.9 0.9 ZDEDC --- --- --- --- 0.8 0.8 --- --- --- --- Shore A Hardness, Instantaneous ASTM D2240 Shore D Hardness, Instantaneous ASTM D2240 100% Modulus, psi ASTM D412 Tensile Strength, psi ASTM D412 Flexural Modulus, psi ASTM D790 Ultimate Elongation, % ASTM D412 Set at Break, % ASTM D412 Tension Set, % ASTM D412 Compression Set B, Piled ASTM D395 22 Hrs. @ RT, % 22 Hrs. @ 50°C, % Spiral Flow, cm @ 800 psi Length of filled portion of a spiral-shaped mold having mold pathway of 0.3 cm diameter at 260°C Examples 1, 2, 3, 4, 5 and 6 are binary DVA blends (i.e. a thermoplastic resin and a single rubber component) and Examples 7, 8, 9 and 10 are ternary DVA blends (i.e. a thermoplastic resin and two rubber components). Examples 1, 3 and 5 are comparative binary DVA blends made in accordance with U.S. Patent No. 4,639,487 utilizing ethylene-vinyl acetate copolymer as the thermoplastic resin. Examples 2, 4 and 6 are binary DVA blends which are identical in composition to the comparative blends except for the use, in accordance with this invention, of a plastomeric ethylene-hexene copolymer as the thermoplastic resin rather than an ethylene-vinyl acetate (EVA) copolymer. As shown by the measured shore hardness values, the DVA blends of the invention, Examples 2, 4 and 6, are in each case softer that their counterpart DVA blends utilizing EVA. Likewise the DVA blends of the invention exhibit greater elasticity than their counterpart comparative DVA blends as measured by a lower set at break value. Each DVA blend of the invention exhibits a comparable or higher resiliency as shown by its comparable or lower compression set value than the comparative blends. The highly oil extended DVA blends of Examples 2 and 4 show a moderately lower strength based on measured tensile strength and elongation, than their comparative counterparts whereas the DVA blend of Example 6 possesses comparable strength compared to its counterpart. Examples 7, 8, 9 and 10 are ternary DVA blends utilizing two different rubber components namely chlorinated butyl rubber and neoprene. The DVA blends of Examples 7 and 9 are comparative blends made in accordance with U.S. Patent No. 4,639,487 utilizing as the thermoplastic resin either an ethylene-vinyl acetate copolymer (Example 7) or an ethylene-methylacrylate copolymer (Example 9). Examples 8 and 10 are DVA blends made in accordance with this invention utilizing a plastomeric ethylene-hexene copolymer as the thermoplastic resin, but otherwise are identical in composition to their respective comparative counterpart DVA blends. Each DVA blend of the invention, Examples 8 and 10, exhibits greater flexibility and softness as shown by their lower values for flexural modulus and shore hardness than their counterpart comparative DVA blends. Each DVA blend of the invention has comparable or increased elasticity although each has decreased tensile strength in comparison. It is believed that the apparently greater tensile strength of the EVA-based ternary blend DVA of Example 7 is due to the thermal instability of the high vinyl acetate content copolymer thermoplastic resin which, at high processing temperatures, undergoes homolytic cleavage to liberate acetic acid which results in intermolecular cross-linking in the thermoplastic matrix. Dumbbells of the DVA composition of Examples 7 and 8 were molded at 240°C with sequentially longer residence times in the injection press. As the residence time increased it became impossible to mold a complete dumbbell of the Example 7 DVA composition whereas complete dumbbells were always molded with the Example 8 DVA composition. Whereas the Example 7 DVA composition was rheologically unstable at the 240°C processing temperature and would undergo a cure to a thermoset state rendering it impossible to complete the molding of a dumbbell, the Example 8 DVA composition was completely rheologically stable under identical condition. Although the invention has been described with reference to its preferred embodiments, those of ordinary skill in the art may, upon reading this disclosure, appreciate changes and modifications which may be made which do not depart from the scope and spirit of the invention as described above or claimed hereafter.

Claims: A thermoplastic elastomeric composition, characterized in that it comprises (a) a thermoplastic resin containing at least 25 wt %, based upon the weight of the thermoplastic resin, of a plastomeric copolymer selected from the group consisting of ethylene-hexene copolymer, ethylene-butene copolymer and mixtures thereof, said hexene or butene content of the respective copolymers being from 20 wt % to 50 wt.% and said plastomeric copolymer having a density of less than 0.900 and a degree of crystallinity measured as a heat of fusion from 5 to 85 J/g, and (b) a rubber selected from the group consisting of butyl rubber, halogenated butyl rubber, ethylene-propylene-diene rubber (EPDM), polyisoprene, polychloroprene, styrene-butadiene rubber, nitrile rubber, chlorosulfonated polyethylene and mixtures thereof, said rubber having been non-peroxide dynamically vulcanized to a fully cured state in the presence of said plastomeric copolymer. Composition according to claim 1, characterized in that the thermoplastic resin component (a) includes from 35 to 100 wt % of ethylene-hexene copolymer, ethylene-butene copolymer or mixtures thereof and from 0 to 65 wt % of a polyolefin resin having a melt point of less than 126°C. Composition according to any one of the preceding claims, characterized in that it further comprises as part of the thermoplastic resin component (a) a polyolefin resin selected from the group consisting of LDPE, LLDPE and polybutylene. Composition according to any one of the preceding claims, characterized in that the thermoplastic resin component (a) comprises from 20 to 90 wt % of the thermoplastic resin plus rubber components (a) + (b) of the composition and the dynamically vulcanized rubber component (b) comprises from 10 to 80 wt % of the thermoplastic resin plus rubber components (a) + (b) of the composition. Composition according to any one of the preceding claims, characterized in that the thermoplastic resin component (a) comprises from 30 to 80 wt % of the thermoplastic resin plus rubber components (a) + (b) of the composition and the dynamically vulcanized rubber component (b) comprises from 20 to 70 wt % of the thermoplastic resin plus rubber components (a) + (b) of the composition. Composition according to any one of the preceding claims, characterized in that the thermoplastic resin component (a) comprises from 40 to 60 wt % of the thermoplastic resin plus rubber components (a) + (b) of the composition and the dynamically vulcanized rubber component (b) comprises from 40 to 60 wt % of the thermoplastic resin plus rubber components (a) + (b) of the composition. Composition according to any one of the preceding claims, characterized in that the dynamically vulcanized rubber is a halogenated butyl rubber. Composition according to claim 7, characterized in that the halogenated butyl rubber is selected from the group consisting of chlorinated butyl rubber and brominated butyl rubber. Composition according to any one of the preceding claims, characterized in that 0 to 25 wt % based on total rubber, of an uncured rubber is incorporated therein. Composition according to claim 9, characterized in that 5 to 20 wt %, based on total rubber, of an uncured rubber is incorporated therein. Composition according to any one of claims 9 and 10, characterized in that the uncured rubber is selected from the group consisting of EPM, EPDM, polyisobutylene, natural rubber and butyl rubber. Composition according to any one of the claims 9 to 11, characterized in that the uncured rubber is an EPM and the dynamically vulcanized rubber is a halogenated rubber. Composition according to claim 12, characterized in that the halogenated rubber is selected from the group consisting of chlorinated butyl rubber and brominated butyl rubber. Composition according to any one of the preceding claims, characterized in that said plastomeric copolymer has a density of from 0.870 to 0.900. Composition according to any one of the preceding claims, characterized in that said plastomeric copolymer has a melt index ranging from 0.3 to 50. A process for preparing a dynamically vulcanized composition comprising a thermoplastic resin and a fully vulcanized rubber, characterized in that it comprises the steps of : (a) blending a thermoplastic resin comprising a plastomeric copolymer selected from the group consisting of ethylene-hexene copolymer, ethylene-butene copolymer and mixtures thereof, said hexene or butene content of the respective copolymers being from 20 wt % to 50 wt %, said plastomeric copolymer having a density of less than 0.900 and a degree of crystallinity measured as a heat of fusion of from 5 to 85 J/g and rubber at a temperature above the melting point of said resin to produce a blend, said rubber being selected from the group consisting of butyl rubber, halogenated butyl rubber, ethylene-propylene-diene rubber (EPDM), polyisoprene, polychloroprene, styrene-butadiene rubber, nitrile rubber, chlorosulfonated polyethylene, and mixtures thereof; (b) adding a non-peroxide cure system effective for dynamically vulcanizing only said rubber in said blend; and (c) vulcanizing said rubber under dynamic vulcanization conditions for a time sufficient to vulcanize fully said rubber and produce a dynamically vulcanized blend. Process according to claim 16, characterized in that it further comprises incorporating an additional rubber not vulcanizable by the cure system. Process according to claim 17, characterized in that said incorporating of the additional non-vulcanizable rubber is simultaneous with said blending of a thermoplastic resin, plastomeric copolymer and rubber and prior to said vulcanizing. Process according to claim 17, characterized in that said step of incorporating of an additional rubber is after said vulcanizing of the rubber and further comprises shearing mixing until the additional rubber is uniformly dispersed in the dynamically vulcanized blend. Process according to any one of claims 16 to 19, characterized in that it further comprises incorporating an additional rubber after the rubber is fully vulcanized; said additional rubber being vulcanizable by the cure system; provided, however, that the cure system is fully consumed during the vulcanizing step and is unavailable to vulcanize any part of the additional rubber. Process according to any one of claims 16 to 19, characterized in that it further comprises incorporating an additional rubber which is vulcanizable by the cure system to the blend after the rubber is fully vulcanized; said cure system being present in an amount sufficient to at least partially cure the additional rubber, but insufficient to fully vulcanize the additional rubber.

Inventors: HAZELTON DONALD ROSS, PUYDAK ROBERT CHESTER, HAZELTON, DONALD ROSS, PUYDAK, ROBERT CHESTER
Applicants: ADVANCED ELASTOMER SYSTEMS, ADVANCED ELASTOMER SYSTEMS, L.P.
Application year: 1990
Main classification: C08L23
IPC codes: C08L23, C08L21, C08L91, C08L11, C08J3