Thermoplastic elastomers based upon chlorinated polyethylene and a crystalline polypropylene

Abstract: Thermoplastic vulcanizates are prepared by curing, at least partially by dynamic vulcanization, blends of chlorinated polyethylene and crystalline thermoplastic polymers especially polyethylene or polypropylene. Inclusion of a plasticizing material or extender oil, e.g. trioctyl trimellitate, enhances softness and oil resistance of the blends. Vulcanizing materials include a basic material, normally added with the chlorinated polyethylene, and a derivative of 2,5-dimercapto-1,3,4-thiadiazole or a combination of 2,5-dimercapto-1,3,4-thiadiazole and an activator material such as an amine having a boiling point of 110°C or higher and a pK value less than 4.5.

Description: The present invention generally concerns thermoplastic elastomer compositions comprising blends of chlorinated polyethylene (CPE) and a crystalline thermoplastic polypropylene. The present invention also concerns preparation of said compositions by dynamic vulcanization or by a sequential combination of dynamic vulcanization and static curing. Static curing may occur, for example, in a heated oven. The present invention further concerns the use of a nonperoxide cure package to accomplish said dynamic vulcanization. Thermoplastic elastomers which can be processed and fabricated by methods used for thermoplastics and do not require vulcanization to develop elastomeric properties are known (see, for example, US-A-No. 3,265,765, as well as Hartman et al, "Butyl Grafted to Polyethylene Yields Thermoplastic Elastomer," Rubber World , October 1970, pp. 59-64). Dynamic vulcanization is a process whereby a blend of plastic, rubber and rubber curative is masticated while curing the rubber. The term "dynamic" indicates the mixture is subjected to shear forces during the vulcanisation step as contrasted with "static" vulcanization wherein the vulcanizable composition is immobile (in fixed relative space) during vulcanization. One advantage of dynamic vulcanization is that elastoplastic (thermoplastic elastomeric) compositions may be obtained when the blend contains the proper proportions of plastic and rubber. Dynamic vulcanization processes are described in US-A-3,037,954; US-A-3,806,558; US-A-4,104,210; US-A-4,116,914; US-A-4,130,535; US-A-4,141,863; US-A-4,141,878; US-A-4,173,556; US-A-4,207,404; US-A-4,271,049; US-A-4,287,324; US-A-4,288,570; US-A-4,299,931; US-A-4,311,628 and US-A-4,338,413. Known dynamic vulcanization processes are believed to be somewhat unsuitable for making soft compositions because as the rubber level rises the resulting compositions become less fabricable. In other words, the compositions give poor extrudates and, sometimes, cannot be extruded at all. Accordingly, there is a need for processes for preparing soft, extrusion-fabricable, thermoplastic elastomeric compositions. US-A-4,130,535 discloses thermoplastic vulcanizates or blends of polyolefin resin and mono-olefin copolymer rubber which are processable in the same manner as thermoplastics even though the rubber is fully cured. The thermoset state is avoided by simultaneously masticating and curing the blends. The blends comprise from 25 to 95 percent by weight of the resin and from 75 to 5 percent by weight of the rubber. Oil extended vulcanizates have a ratio of from 35 to 65 percent of the resin and from 65 to 35 percent of the rubber. Peroxide, azide and sulfur vulcanizing agents may be used to effect curing of the rubber. Typical monoolefin copolymer rubbers include saturated EPM (ethylene-propylene rubbers) or unsaturated EPDM (ethylene-propylene-diene terpolymer rubbers). US-A-4,594,390 teaches that improved thermoplastic elastomer materials are obtained when a composition comprising polypropylene, an EPDM rubber, an extender oil and a curative is masticated at a shear rate of at least 2000 sec⁻¹. Suitable results are obtained with shear rates of from 2500 to 7500 sec⁻¹. US-A-4,207,404 discloses thermoplastic elastomer compositions prepared by dynamic vulcanization of blends of CPE and nylon in the presence of a peroxide vulcanizing agent. US-A-3,806,558 discloses partially cured blends of a monoolefin copolymer rubber, such as those disclosed in US-A-4,130,535, and a polyolefin plastic, usually polyethylene or polypropylene. The blend is mixed with a small amount of curative, and subjected to curing conditions while working the mixture dynamically. A. Y. Coran, R. P. Patel and D. Williams, in an article entitled "Rubber-Thermoplastic Compositions, Part V, Selecting Polymers for Thermoplastic Vulcanizates," Rubber Chemistry and Technology , Vol. 55, 116 (1982), describe approximately 100 thermoplastic vulcanizate compositions, based on 9 kinds of thermoplastic resins and 11 kinds of rubber. All compositions contain 60 parts of rubber and 40 parts of plastic. They prepare these compositions by melt mixing the plastic, rubber and other components in a Brabender or Haake mixer. Generally, the plastic, rubber and other components of the composition, except for curatives, are mixed at controlled elevated temperatures (Table I) for from 2 to 6 minutes during which time the plastic melts and a blend is formed with the rubber. After blend formation, curatives are added to cross-link the rubber, and mixing is continued until a maximum consistency or mixing torque is observed. Each composition is removed from the mixer and then remixed for an additional minute in the molten state to insure uniformity of the mixture. One of the rubber materials is CPE. The plastic materials, listed in Table I on page 117, include polypropylene (PP), polyethylene (PE), polystyrene (PS), an acrylonitrile-butadiene-styrene polymer (ABS), a styrene-acrylonitrile copolymer (SAN), polymethyl methacrylate (PMMA), polytetramethylene terephthalate (PTMT), Nylon-6,9 (PA) and polycarbonate (PC). One of the mechanical properties, tension set (ASTM D412-66), is determined by stretching 51 mm long specimens to 102 mm for 10 minutes then by measuring set after 10 minutes relaxation. CPE compositions are cured by peroxides, specifically 2,5-dimethyl-2,5-bis(t-butyl peroxy)hexane. Tension set values abstracted from Table IX at page 125 are as follows: (a) CPE/PP - 55 percent; (b) CPE/PE - 58 percent; (c) CPE/ABS - 65 percent; (d) CPE/ABS - 91 percent; (e) CPE/PMMA - 82 percent; (f) CPE/PTMT - 40 percent; (g) CPE/PA - 59 percent; and (h) CPE/PC - 85 percent. They note that the 40 percent value may not be accurate because the CPE is insufficiently stable to withstand processing at the high melt temperatures for PTMT. FR-A-2356687 (corresponding to US-A-4128510) discloses the cross-linking of halogen-containing polymers with 2,5-dimercapto-1,3,4-thiadiazole derivatives and a basic material. Reference is made to cross-linking CPE (see, for example, FR page 6, lines 15/16; page 7, lines 11 and 23/24; Example 14 and Examples 36 and 37). Although reference is made to the cross-linking of halogen-containing polymers blended with non-halogen-containing polymers, there is no teaching specifically relevant to the preparation of thermoplastic vulcanizates. Further, there is no teaching indicating the effect on elastomeric properties of the use of dimercaptothiadiazole derivatives compared with other cross-linking agents. One aspect of the present invention is a process for preparing a thermoplastic elastomer material from a blend of an amorphous chlorinated polyethylene (CPE) and a crystalline thermoplastic polypropylene, the process comprising: a. forming a heat-plastified, substantially uniform admixture comprising 100 parts by weight (pbw) of an amorphous CPE, 5 to 150 pbw of a plasticizing material compatible with the CPE, 12 to 150 pbw of a crystalline thermoplastic polypropylene, and a basic material present in an amount sufficient to heat stabilize the CPE, said basic material being selected from basic metal oxides and hydroxides and their salts with weak acids; and b. dispersing a vulcanizing material for the CPE throughout the admixture while mixing said admixture at a temperature sufficient to activate the vulcanizing material without substantially degrading any component of the composition and for a period of time sufficient to cure partially or substantially all of the CPE, the vulcanizing material comprising a vulcanizing derivative of 2,5-dimercapto-1,3,4-thiadiazole or a combination of 2,5-dimercapto-1,3,4-thiadiazole and an activator material. Where partial curing of the CPE has taken place, completing vulcanization of the CPE is conducted via static curing. The present invention also relates to the thermoplastic elastomer composition obtainable by the process of the invention and comprising a blend of 100 parts by weight (pbw) of an amorphous CPE, from 12 to 150 pbw of a crystalline thermoplastic polypropylene resin, and a plasticizing material in an amount of from 5 to 150 pbw, the composition being processable in an internal mixer to provide a product which forms an essentially continuous sheet following transfer, with the resin components in a heat-plastified state, to the rotating rolls of a rubber mill. These materials have a tension set value, at 100 percent elongation (ASTM D 412), of less than 50 percent. Materials having tension set values of greater than 50 percent are believed to be unsuitable for use as elastomers. The crystalline thermoplastic polymer is a polypropylene. Crystalline block copolymers of ethylene and propylene (which are plastics distinguished from amorphous, random ethylene-propylene elastomers) can also be used. Included among the polypropylene resins are the higher alpha-olefin modified polypropylenes (see, "Polyolefins," N. V. Boenig, Elsevier Publishing Co., N.Y. 1966). Materials other than crystalline thermoplastic polypropylene may be used in conjunction with the amorphous CPE provided such materials are mechanically compatible with the CPE. "Mechanically compatible", as used herein, means that the polymers form a two-phase mixture that does not undergo substantial delamination. Illustrative materials believed to meet this criterion include glassy polymers such as polycarbonates, styrene-acrylonitrile copolymers and terpolymers of acrylonitrile, butadiene and styrene. CPE starting materials suitable for purposes of the present invention preferably are finely-divided particles which meet four physical property criteria. First, the materials have a weight average molecular weight of from 40,000 to 300,000. Second, the materials have a chemically combined chlorine content of from 20 to 48 percent by weight of polymer. Third, the materials have a 100 percent modulus, measured in accordance with ASTM Test D-412, from 0.5 to 4.8 MPa. Fourth, the materials have a relative crystallinity of from 0 to 15 percent, preferably from 0 to 2 percent. CPE meeting the aforementioned physical property criteria can be prepared by a chlorination process of the type disclosed in US-A-3,454,544. Satisfactory CPE is readily obtained by practice of a chlorination process which comprehends suspension chlorination, in an inert medium, of a finely divided, essentially linear polyethylene or olefin interpolymer. The interpolymer contains at least 90 mole percent ethylene with the remainder being one or more ethylenically unsaturated monomers polymerizable therewith. The polymer is first chlorinated at a temperature below its agglomeration temperature for a period of time sufficient to provide a partially chlorinated polymer having a chlorine content of from 2 to 23 percent chlorine, based on the total weight of polymer. This is followed by sequential suspension chlorination of the partially chlorinated polymer, in a particulate form, at a particular temperature. The particular temperature is, with respect to the olefin interpolymer, above its agglomeration temperature but at least 2°C below its crystalline melting point. Sequential chlorination is continued for a period of time sufficient to provide a chemically combined chlorine content of up to 48 percent by weight of polymer. Useful ethylenically unsaturated monomers include nonaromatic hydrocarbon olefins having three or more carbon atoms such as propylene, butene-1, 1,4-hexadiene, 1,5-hexadiene, octene-1, 1,7-octadiene, and 1,9-decadiene; substituted olefins such as acrylic acid, and acrylic acid esters; alkenyl aromatic compounds such as styrene and its derivatives, and other known polymerizable materials. The temperature at which chlorination normally leads to agglomeration of polymer particles depends to a large extent on the nature and molecular weight of the polymer to be chlorinated. In the case of crystalline and predominantly straight chain polyethylenes having a branching of the chains of less than one methyl group per 100 carbon atoms and a density of at least 0.94 g/cm³, the temperature is above 95°C, in particular above 100°C or even above 110°C. In the case of polyethylenes having a relatively marked branching of the chains and a lower density, the temperature is lower, about 65°C. The temperature employed in the sequential chlorination should be greater than that employed in the initial chlorination in order to prevent retention of excessive undesirable crystallinity and formation of nonuniformly chlorinated polymer. The temperature employed in the sequential chlorination should also be below the crystalline melting point of the polymer being chlorinated in order to prevent accelerated particle size growth and development of undesirable agglomeration of polymer particles. After a polyolefinic material has been suspension chlorinated to a desired degree, it may easily be filtered from suspension in the inert suspending liquid, washed and dried to prepare it for subsequent use. The present invention is not restricted to CPE prepared by suspension or slurry chlorination procedures. Solution chlorination and bulk, or fluidized bed, chlorination procedures may also be used provided the polymers produced thereby meet the aforementioned requirements with regard to chlorine content and residual crystallinity. The thermoplastic elastomers or vulcanizates of the present invention are cured with a cure package comprising a basic material and 2,5-dimercapto-1,3,4-thiadiazole or a derivative thereof. These cure packages are disclosed in US-A-4,128,510 and US-A-4,288,576. Peroxide cure packages are believed to be unsuitable for use in curing blends as disclosed herein. Physical properties and handling characteristics of the blends indicate either a lack of sufficient crosslinking or at least partial degradation of the polypropylene. Illustrative derivatives of 2,5-dimercapto-1,3,4-thiadiazole include: wherein X is a substituent selected from hydrogen, ―CRR'OH, ―(CH₂―CH―O) n H, wherein m is an integer of from 2 to 10; n is an integer from 1 to 5; R and R' are selected from hydrogen, alkyl groups containing from 1 to 8 carbon atoms, and aryl, alkaryl or aralkyl groups containing 6 to 8 carbon atoms; R² is an alkyl group containing from 1 to 17 carbon atoms, an aryl group containing 1 or 2 rings, an alkaryl group containing from 7 to 14 carbon atoms, an aralkyl group containing from 7 to 8 carbon atoms or a cyclohexyl group; and R³ is an alkyl group containing from 1 to 8 carbon atoms. X' can be the same as X with the exception of hydrogen and Y is zinc, lead, ―CRR'― , ―S― , ―SO₂― , ―SS― , wherein R⁴ is an alkylene or alkenylene group containing from 1 to 8 carbon atoms, or a cycloalkylene, arylene or a alkarylene group containing from 6 to 8 carbon atoms; z is 0 or 1; and R⁵ is an alkylene group containing from 2 to 8 carbon atoms or a phenylene, methylphenylene or methylenediphenylene group. Basic materials suitable for use in conjunction with derivatives of 2,5-dimercapto-1,3,4-thiadiazole include inorganic materials such as basic metal oxides and hydroxides and their salts with weak acids, such as, for example, magnesium hydroxide, magnesium oxide, calcium oxide, calcium hydroxide, barium oxide, barium carbonate, sodium phenoxide and sodium acetate. These basic materials also serve as heat stabilizers for CPE. Thus, they are beneficially admixed with the CPE before the polymer blend is converted to a heat-plastified admixture rather than in conjunction with the thiadiazole derivative. Additional basic material may, if desired, be added together with the thiadiazole derivative. Other basic materials may also be used so long as they do not promote degradation of one of the components of the blend or deactivate the vulcanizing materials. The basic material is preferably magnesium oxide or magnesium hydroxide. Basic or activator materials suitable for use in conjunction with 2,5-dimercapto-1,3,4-thiadiazole include amines having a boiling point above 110°C and a pK value below 4.5, salts of amines having pK values below 4.5 with acids having pK values above 2.0, quaternary ammonium hydroxides and their salts with acids having pK values above 2.0, diphenyl- and ditolyl-guanidines, and the condensation product of aniline and at least one mono-aldehyde containing 1 to 7 carbon atoms, in combination with at least an equal amount of an inorganic base. The term "pK value" refers to the dissociation constants of bases and acids in aqueous solution. Representative values are shown in the Handbook of Chemistry and Physics , 45th Edition, The Chemical Rubber Co., page D-76 (1964). As noted in the preceding paragraph, a certain amount of a basic material such as magnesium oxide or magnesium hydroxide must also be present to heat stabilize the CPE. The plasticizing material is suitably selected from trimellitate esters, phthalate esters, aromatic oils or polyesters of dlcarboxylic acids containing from 2 to 10 carbon atoms. The plasticizing material is desirably trioctyl trimellitate. The ingredients, save for the vulcanizing material, are mixed at a temperature (eg 120° to 220°C) sufficient to soften the crystalline thermoplastic polypropylene or, more commonly, at a temperature above its melting point if the polypropylene is crystalline at ordinary temperatures. Blending is carried out for a time sufficient to form a generally uniform blend of the components. It is accomplished by any one of a number of conventional techniques, for example, in an internal mixer, two-roll mill or extruder. In the preferred embodiment the heat-plastified substantially uniform admixture is formed in at least two sequential steps comprising: (i) forming a heat-plastified, substantially uniform admixture by mixing the CPE, the plasticizing material and the basic material at a temperature (eg 25°C to 150°C) sufficiently high to heat plastify the CPE with substantially no degradation thereof; and (ii) dispersing the thermoplastic polypropylene throughout the admixture while heating said admixture to a temperature (eg 175°C to 220°C) above the polypropylene's crystalline melting point but below a temperature at which substantial degradation of the CPE occurs. After the resin and rubber are intimately mixed, the vulcanizing material is added. Heating and masticating the blend components at vulcanization temperatures are generally adequate to complete curing in a few minutes. If shorter vulcanization times are desired, higher temperatures may be used, provided they are low enough to preclude substantial degradation of the CPE. Suitable vulcanization temperatures range from about the melting temperature of the crystalline thermoplastic polymer (about 175°C in the case of polypropylene) to 250°C or more. A preferred range of vulcanization temperatures is from 180°C to 200°C. Thermoplastic vulcanizates are beneficially prepared by continuously mixing the compositions, after the vulcanizing material is added, until vulcanization is complete. If desired from an economic point of view, completion of vulcanization may be accomplished by static vulcanization provided sufficient curing by dynamic vulcanization has occurred before static vulcanization begins. If insufficient dynamic vulcanization occurs, an unprocessable thermoset vulcanizate may be obtained. Physical property values from a hybrid of dynamic vulcanization and static vulcanization, where adequate dynamic vulcanization has occurred, do not differ appreciably from those obtained from blends cured solely by dynamic vulcanization. By way of illustration, sufficient dynamic vulcanization occurs in as little as 1 minute in a heated mixer operating at a temperature of 204°C if the components of the blend are premixed. Without premixing, 5 minutes or even longer may be required to achieve sufficient dynamic vulcanization in such a heated mixer. If appreciable static curing occurs before the rubber is dispersed and the thermoplastic becomes a continuous phase, an unprocessable thermoset vulcanizate may be obtained. A convenient measure of the state of cure of the thermoplastic elastomer compositions of the present invention is obtained by comparing the tensile strength of the blend before and after dynamic vulcanization. The dynamically vulcanized blend using a thiadiazole cure package suitably has a tensile strength of about 1.3 megapascals (MPa) and desirably 3.4 MPa or more greater than that of the unvulcanized blend or the peroxide cured blend. The properties of the thermoplastic vulcanizates of this invention may be modified, either before or after vulcanization, by adding ingredients which are conventional in the compounding of CPE elastomers, polyolefin resins and blends thereof. Skilled artisans will recognize, however, that CPE compounding additives generally must be added before vulcanization if they are to have an effect upon the CPE. The timing of addition is not as critical for addition of ingredients to the thermoplastic portion of the materials of the present invention. Examples of suitable ingredients or additives include various carbon blacks, alumina, silica, titanium dioxide, calcium carbonate, colored pigments, clays, zinc oxide, stearic acid, accelerators, vulcanizing agents, sulfur, stabilizers, antioxidants, antidegradants, processing aids, adhesives, tackifiers, plasticizers, processing aids such as lubricants and waxes, prevulcanization inhibitors, discontinuous fibers such as glass fibers and wood cellulose fibers, and extender oils. The amounts used depend, at least in part, upon the quantities of other ingredients in the composition and the properties desired from the composition. Minor amounts of other saturated and unsaturated polymers such as alpha-olefins may be added to reduce the cost or modify the properties of the composition. The addition of carbon black or an extender oil or both is recommended, particularly if accomplished prior to dynamic vulcanization. Carbon black improves the tensile strength, and extender oil can improve the resistance to oil swell, heat stability, hysteresis, cost and permanent set of the thermoplastic vulcanizate. The addition of extender oil can also improve processability. Aromatic, naphthenic and paraffinic extender oils provide satisfactory results so long as they are used in amounts which do not exceed their limits of compatibility with CPE. Suitable extender oils are identified in Rubber World Blue Book, Materials and Compounding Ingredients for Rubber (1975), pages 145-190. The quantity of extender oil added depends upon the properties desired. The upper limit, which depends upon the compatibility of a particular oil and blend ingredients, is exceeded when excessive exudation of extender oil occurs. Typically, from 5 to 150 parts by weight (pbw) extender oil are added per 100 pbw of CPE. Commonly, from 30 to 125 pbw of extender oil are added per 100 pbw of CPE present in the blend with quantities of from 70 to 100 pbw of extender oil per 100 pbw of CPE being preferred. Typical additions of carbon black comprise from 20 to 250 pbw of carbon black per 100 pbw of CPE and usually from 20 to 100 pbw carbon black per 100 pbw of CPE. The amount of carbon black which can be used depends, at least in part, upon the type of carbon black and upon the amount of extender oil to be used. Thermoplastic elastomeric vulcanizates prepared as described herein are useful for making a variety of articles such as tyres, hoses, belts, gaskets, moldings and molded parts. They are particularly useful for making articles by extrusion, injection molding and compression molding techniques. They also are useful for modifying thermoplastic resins in general and polyolefin resins in particular. The vulcanizates are suitably blended with thermoplastic resins using conventional mixing equipment. The properties of the modified resin depend upon the amount of vulcanizate blended. Generally, the amount of vulcanizate is sufficient to provide from 5 to 25 pbw of CPE per 100 pbw of the modified resin. In the following examples, all parts and percentages are by weight unless otherwise specified. Arabic numerals are used to identify examples representing the present invention whereas alphabetic characters are used to designate comparative examples. Sample Preparation A 1450 cubic centimeter (cm³) capacity Banbury mixer is used to provide initial melt compounding of all blends and, when appropriate curative components are added and activated, at least partial curing of said blends. Further mixing and, if needed, completion of curing takes place when the contents of the Banbury mixer are placed on a heated two-roll mill. Curing may also be completed in a static cure oven. A. Multiple Step Banbury Mix Procedure 1. Prepare a rubber masterbatch by adding CPE, stabilizers, fillers, plasticizers and other additives to the Banbury mixer while it is operating at low speed (about 77 revolutions per minute (rpm)) and cooling water is circulating through the front and rear rotors, right and left sides and fixed sections of the Banbury mixer. As noted hereinabove, the base to be used in conjunction with the vulcanizing material may also function as the stabilizer. The amounts of masterbatch components are sufficient to fill the mixing cavity. Mixing continues for about 4 minutes at which time the temperature of the contents reaches approximately 163°C. 2. Remove part of the masterbatch, replace it with an amount of crystalline thermoplastic polypropylene and continue mixing for about 5 minutes at a temperature of about 176°C. The temperature of the contents is controlled by varying the mixer speed. 3. Remove the blend from the Banbury mixer and place it on a two-roll rubber compounding mill operating at a set temperature of about 21°C with a gap between the rolls of about 5 mm. 4. After cooling the blend on the two-roll mill for a period of about 2 minutes, add components to be used in vulcanizing the blend (also known as the "cure package") and continue mixing for a period of about 2 minutes. 5. Remove the roll milled blend (also known as "the blanket") from the two-roll mill, cut it into strips and add the strips to the Banbury mixer which is operating at a set temperature of from 176°C to 188°C. Mixing and curing of the CPE continues for about 7 minutes with temperature control as in Step 2. This period of time is generally sufficient to completely cure the CPE component of the blend. 6. Remove the contents of the Banbury mixer and mix for 2 minutes on a hot two-roll mill, heated with 150 psi steam (1050 kPa) with a gap between the rolls of about 5 mm. This final mixing on the roll mill is done to assure that uniform samples are used to prepare compression molded samples for testing. Remove the contents from the mill in the form of a sheet having a thickness of about 1.7 mm. 7. Compression mold the sheets to a thickness of about 1.5 mm using a heated (about 189°C) press. The press and its contents are first preheated with no applied force for 2 minutes. The contents are then pressed for 3 minutes with an applied force of 20 tons, cooled for 4 minutes with an applied force of 20 tons and then removed from the press after the force is relieved. The compression molded sheets are used for physical property characterization. B. Single Load Banbury Mix Procedure 1. Same as Step 1 of the Multiple Step Banbury Mix Procedure except that the mixer is not completely filled with rubber masterbatch components. In other words, there is sufficient room to add the crystalline thermoplastic polypropylene without the necessity of removing a portion of the masterbatch. 2. Add an amount of crystalline thermoplastic polymer and continue mixing for about 5 minutes at a temperature of about 176°C. The amount is generally sufficient to fill the mixer. The temperature of the contents is controlled by varying the mixer speed. 3. Add the vulcanizing material to the blend while continuing mixing. The vulcanizing material is placed in a small bag formed from an ethylene/acrylic acid copolymer commercially available from The Dow Chemical Company under the trade designation PRIMACOR™. The bag is used to minimize, if not eliminate, loss of vulcanizing material to the wall of the mixer. Mixing and curing continues for about 7 minutes at a temperature of from 176°C to 188°C. As noted herein, at Step 5 of the Multiple Step Procedure, this period of time is generally sufficient to completely cure the CPE component of the blend. 4. Same as Step 6 of the Multiple Step Banbury Mix Procedure. 5. Same as Step 7 of the Multiple Step Banbury Mix Procedure. Test Procedures The following American Society for Testing and Materials (ASTM) Tests are used to characterize the physical properties of materials prepared in accordance with Procedures A and B above: Specific Gravity ASTM Method D792 Hardness ASTM Method D2240 Tensile Strength ASTM Method D412 Elongation ASTM Method D412 Modulus ASTM Method D412 Tension Set ASTM Method D412 Compression Set ASTM Method D395B Oil Resistance ASTM Method D471 Heat Resistance ASTM Method D573 Examples 1-3 - CPE/PP Thermoplastic Elastomer Using the Multiple Step Banbury Mix Procedure (Procedure A) or the Single Load Banbury Mix Procedure (Procedure B), sample sheets are prepared from the composition shown in Table I. In Example 1, the amount of trioctyl trimellitate is 85 parts and the amount of polypropylene is 56.0 parts. In Examples 2 and 3, the amount of trioctyl trimellitate is 100 parts and the amount of polypropylene is 59.9 parts. EXAMPLE 1 COMPOSITION Parts/Hundred Parts of CPE Component Description/Source-Purpose 30 carbon black N330 - filler material 5.2 hydrated amorphous silica, commercially available from PPG Industries, Inc. under the trade designation HISIL™ 223 - filler material 5.2 magnesium oxide, commercially available from Elastochem Inc. under the trade designation MAGLITE#TRM# D - activator 85 or 100 trioctyltrimellitate - oil extender 100 chlorinated polyethylene, commercially available from The Dow Chemical Company under the trade designation TYRIN™ CMO136 - rubber 56.0 or 59.9 polypropylene, commercially available from Himont, Inc. under the trade designation PRO-FAX™ 6723 - thermoplastic 3.0 5-mercapto-1,3,4-thiadiazole-2-thiobenzoate, commercially available from Hercules Inc. under the trade designation ECHO-S™ - curative Physical property test values obtained from said sample sheets are summarized in Table II. PHYSICAL PROPERTY DATA FOR EXAMPLES 1-3 Process/Physical Property (Unit of Measure) Physical Property Measured Value Ex. 1 Ex. 2 Ex. 3 Process A A B Specific Gravity 1.12 1.11 1.11 Hardness, Shore A 80 78 82 Ultimate Tensile (psi/MPa) 1128/7.78 1087/7.49 1192/8.22 Elongation (%) 258 292 256 100% Modulus (psi/MPa) 608/4.19 548/3.78 670/4.62 200% Modulus (psi/MPa) 946/6.52 836/5.76 997/6.87 Tension Set @ 100% Elong 16 15 15 Compression Set 100°C/70 Hours 60 63 65 ASTM Oil #2, 132°C/70 Hours Volume Swell (%) 8 5 4 % Tensile Retained 66 62 79 % Elongation Retained 80 57 69 % 100% Modulus Retained 86 99 91 ASTM Oil #3, 132°C/70 Hours Volume Swell (%) 24 20 19 % Tensile Retained 54 57 61 % Elongation Retained 66 64 70 % 100% Modulus Retained 62 74 77 The data presented in Table II demonstrate that similar results are obtained by the single step and multi-step processes. The data also demonstrate that satisfactory results are obtained with two different levels of trioctyl trimellitate. Similar results are expected with other compositions and process variations which fall within the scope of the present invention. Example 4 and Comparative Examples A-B - Cure System Comparison Using the Single Load Banbury Mix Procedure (Procedure B), sample sheets are prepared from compositions similar to that shown in Table I. In Example 4 and Comparative Examples A and B, the amount of trioctyl trimellitate is 100 parts and the amount of polypropylene is 59.9 parts. In Example 4, the amount of accelerator is increased to 1.0 part. In Comparative Example A, no cure package is used and in Comparative Example B, curing is accomplished with a peroxide cure package. The peroxide cure package includes 6.0 parts of α-α'-bis(t-butylperoxy)diisopropylbenzene on Burgess KE Clay, commercially available from Hercules Inc. under the trade designation VUL-CUP™ 40KE and 2.0 parts of triallyl trimellitate (commercially available from C. P. Hall). Physical property test values obtained from said sample sheets are summarized in Table III. The tension set in all three cases was well below 50. CURE SYSTEM COMPARISON Process/Physical Property (Unit of Measure) Physical Property Measured Value Ex. 4 Comp Ex. A Comp Ex. B Process B B B Specific Gravity 1.11 1.10 1.12 Hardness, Shore A 80 78 75 Ultimate Tensile (psi/MPa) 1137/7.84 937/6.46 471/3.25 Elongation (%) 257 533 197 100% Modulus (psi/MPa) 665/4.59 518/3.57 372/2.56 200% Modulus (psi/MPa) 963/6.64 601/4.14 -- Compression Set 100°C/70 Hours 56 87 90 ASTM Oil #2, 132°C/70 Hours Volume Swell (%) 5 13 21 % Tensile Retained 69 51 51 % Elongation Retained 65 24 21 % 100% Modulus Retained 96 84 -- ASTM Oil #3, 132°C/70 Hours Volume Swell (%) 20 47 42 % Tensile Retained 60 34 18 % Elongation Retained 60 18 17 % 100% Modulus Retained 81 -- -- -- not measured The data presented in Table III demonstrate that physical properties are improved when the CPE/PP blends are cured with a thiadiazole cure. The data also demonstrate that physical properties are degraded when the blends are cured with a conventional peroxide cure package. Similar results are obtained with other compositions within the scope of the present invention. Comparison Examples C-F Commercial Thermoplastic Elastomer Physical Properties In order to evaluate the potential suitability of the thermoplastic elastomers of the present invention, four commercially available thermoplastic elastomers are subjected to the same tests as Examples 1 and 2. Comparative Example C is SANTOPRENE™ 201(73), commercially available from Monsanto Co. Comparative Example D is SANTOPRENE™ 201(80), commercially available from Monsanto Co. Comparative Example E is ALCRYN™ 1201B, an oil resistant thermoplastic elastomer commercially available from E. I. DuPont de Nemours & Co. Comparative Example F is GEOLAST™ 701, an oil resistant thermoplastic elastomer commercially available from Monsanto Co. The test results are presented in Table IV which follows. Example 1 is included in Table IV for ease of comparison. PHYSICAL PROPERTY COMPARISON Process/Physical Property (Unit of Measure) Physical Property Measured Value Ex 1 Comp Ex C Comp Ex D Comp Ex E Comp Ex F Specific Gravity 1.12 .968 .966 1.23 1.09 Hardness, Shore A 80 76 80 65 80 Ultimate Tensile (psi/MPa) 1123/7.74 1451/10.00 1494/10.30 1796/12.38 1339/9.23 Elongation (%) 258 513 415 280 200 309 294 100% Modulus (psi/MPa) 608/4.19 472/3.25 598/4.12 608/4.19 548/3.78 200% Modulus (psi/MPa) 946/6.52 607/4.18 813/5.61 1162/8.01 1246/8.59 Tension Set at 100% Elong 16 15 10 6 12 Compression Set 100°C/70 hrs 60 40 40 59 50 Low Temp Britt °C -36 -60 -60 -35 -38 ASTM Oil #2, 121°C/70 Hrs Vol Swell % 8 46 40 4 2 % Tens Ret 66 68 77 103 97 % Elong Ret 80 64 76 93 79 % 100% Mod Ret 86 86 101 94 109 ASTM Oil #3, 121°C/70 Hrs Vol Swell % 24 65 59 17 13 % Tens Ret 54 61 74 82 71 % Elong Ret 66 58 74 78 61 % 100% Mod Ret 62 75 95 85 90 The data presented in Table IV demonstrate that the thermoplastic elastomers of the present invention compare favorably with commercially available materials in terms of physical properties such as tension set at 100 percent elongation, tensile, elongation, oil resistance and low temperature impact resistance. Examples 5-9 - Effect of Different Polypropylene on Properties Using the Single Mix Procedure (Procedure B), sample sheets were prepared from a composition similar to that shown in Table I. The type and amount of filler materials, chlorinated polyethylene, curative and curative co-agent are the same. The amount of trioctyltrimellitate is 100 parts. The following polypropylenes are used in amount of 59.9 parts: PP-A is PRO-FAX™ 6723, 0.8 g/10 min. melt index; PP-B is PRO-FAX™ 6524, 4.0 g/10 min. melt index; PP-C is PRO-FAX™ 6324, 12.0 g/10 min. melt index; PP-D is PRO-FAX™ 6301, 12.0 g/10 min. melt index - unstabilized; and PP-E is PRO-FAX™ 6224, 35.0 g/10 min. melt index. Physical property test values together with the type of polypropylene are shown in Table V. The data presented in Table V demonstrate that high molecular weight polypropylenes (e.g. Ex. 5) produce thermoplastic elastomer materials with higher tensile strength and elongation than lower molecular weight polypropylenes (Ex. 9). The higher molecular weight polypropylenes also have greater tensile strength and elongation values after exposure to oils even though percent property retention does not vary significantly. Similar results are obtained when samples are exposed to air oven aging as well as with other polymer blend compositions within the scope of the present invention. Examples 10-15 - Effect of Extender Oil Type Upon Physical Properties Using the Single Load Banbury Mix Procedure (Procedure B) and, with two exceptions, the composition of Example 4, sample sheets are prepared for physical property testing. One exception is that, for Examples 10 through 15, the magnesium oxide is changed to a magnesium hydroxide commercially available under the trade designation MARINCO™ H from Calgon. The second exception is in the type of extender oil. The extender oils are as follows: Example 10 - TOTM; Example 11 - a high boiling aromatic oil commercially available from R. E. Carroll under the trade designation POLYFLO™ 1172 (hereinafter "AR-1"); Example 12 - a high boiling aromatic oil commercially available from R. E. Carroll under the trade designation SUNDEX™ 8600T (hereinafter "AR-2"); Example 13 - a high boiling aromatic oil commercially available under the trade designation SUNDEX™ 8125 (hereinafter "AR-3); Example 14 - an aromatic oil commercially available from R.E. Carroll under the trade designation SUNDEX™ 790 (hereinafter "AR-4"); and Example 15 - dioctyl phthalate (hereinafter "DOP"). Physical property test results are summarized in Table VI. The data presented in Table VI show that physical property values are generally acceptable for all types of extender oils. The aromatic oils are not as compatible as TOTM with the blends. As such, some bleeding to the surface is observed when aromatic oils are used. The aromatic oils also have less resistance to physical property degradation following thermal aging than TOTM. In addition, low temperature properties are poorer when aromatic oils are used rather than TOTM or DOP or other ester plasticizers. DOP suffers from a similar loss of physical properties following thermal aging. The loss of physical properties following thermal aging, while rendering such compounds unsuitable for high temperature applications such as are experienced in an automobile engine compartment, are not important if the compounds are subjected only to comparatively low temperatures. Similar results are expected with other compounds which are representative of the present invention. Examples 16 - 34 Cure Program Variability Using the composition of Example 4 except that the amount of polypropylene is 60 parts, a variety of cure programs using only dynamic curing (in the Banbury mixer) or a combination of dynamic curing and static curing (in a heated oven) are evaluated. Results of the evaluation are shown in Table VII. The data presented in Table VII demonstrate that a combination of dynamic curing and static curing provides results in terms of physical properties which are generally equivalent to those obtained with dynamic curing, e.g. Example 18 versus Example 25. The reduction in mixer time corresponds to a reduction in cost of the resulting cured blend. Examples 35 - 38 - Effect of CPE Feedstock Melt Index Upon Physical Properties By duplicating the composition of Example 5 save for the type of CPE, samples are prepared for physical property testing. All of the CPE's have a chemically combined chlorine content of 36 percent by weight of polymer and a heat of fusion of 0.2 calories per gram. They differ primarily in terms of the melt index of the feedstock from which they are prepared. Melt index is determined in accordance with ASTM D-1238, condition 190/2.16. In Example 35, the CPE is prepared from a 0.1 decigram per minute feedstock and is commercially available from The Dow Chemical Company under the trade designation TYRIN™ 3615. In Example 36, the CPE is prepared from a 0.3 decigram per minute feedstock and is commercially available from The Dow Chemical Company under the trade designation TYRIN™ CMO136. In Example 37, the CPE is prepared from a 1.0 decigram per minute feedstock and is commercially available from The Dow Chemical Company under the trade designation TYRIN™ CM552. In Example 38, the CPE is prepared from a 6.0 decigram per minute feedstock and is commercially available from The Dow Chemical Company under the trade designation TYRIN™ CMO636. The physical property data are summarized in Table VIII. The data presented in Table VIII highlight three benefits from decreasing the feedstock melt index. First, the tensile strength of the vulcanized blend increases. Second, the tensile set and compression set of the vulcanized blend decrease. Finally, the resistance to oils increases. Similar results are obtained with other compounds which are representative of the present invention. Examples 39 - 42 and Comparative Example G - Effect of Thermoplastic Polymer Amount Upon Physical Properties Using the composition of Example 5, save for the amount of polypropylene, samples are prepared for physical property testing. Table IX includes the amount of polypropylene in parts per 100 parts of CPE as well as in terms of percent by weight of composition. Table IX also displays data from the physical property testing. A review of the data presented in Table IX show that thermoplastic elastomer materials result when polypropylene comprises from 5 to 35 percent of the composition weight (12 to 126 parts per 100 parts of CPE). When the polypropylene fraction increases to about 44 percent of the composition weight (191 parts per 100 parts of CPE), the tension set at 100 percent elongation reaches 50. As noted herein, a value of 50 or greater generally indicates a material unsuitable for use as an elastomer. As such, an upper limit on the amount of this type of polypropylene falls within the range of 126 to 191 parts per hundred parts of chlorinated polyethylene. When the polypropylene fraction falls below about 5 percent (about 12 parts per 100 parts of CPE), the dynamically vulcanized composition exhibits characteristics of a thermoplastic elastomer notwithstanding some mold shrinkage when compression molded samples are prepared. Similar results are expected from other compositions representative of the present invention. Although upper and lower limits on the amount of thermoplastic polymer may vary with the type of polymer, satisfactory results are readily attainable without undue experimentation.

Claims: A process for preparing a thermoplastic elastomer material having a tension set value at 100 percent elongation (ASTM D 412) less than 50 percent comprising: a. forming a heat-plastified, substantially uniform admixture comprising 100 parts by weight (pbw) of an amorphous chlorinated polyethylene (CPE), 5 to 150 pbw of a plasticizing material compatible with the CPE, 12 to 150 pbw of a crystalline thermoplastic polypropylene, and a basic material present in an amount sufficient to heat stabilize the CPE, said basic material being selected from basic metal oxides and hydroxides and their salts with weak acids; and b. dispersing a vulcanizing material for the CPE throughout the admixture while mixing said admixture at a temperature sufficient to activate the vulcanizing material without substantially degrading any component of the composition and for a period of time sufficient to cure partially or substantially all of the CPE, the vulcanizing material comprising a vulcanizing derivative of 2,5-dimercapto-1,3,4-thiadiazole or a combination of 2,5-dimercapto-1,3,4-thiadiazole and an activator material. A process as claimed in claim 1, including the step of completing vulcanization of the partially cured chlorinated polyethylene via static curing. A process as claimed in Claim 1 or claim 2, wherein the heat-plastified admixture includes carbon black in an amount of from 20 to 250 pbw. A process as claimed in any one of the preceding claims, wherein the basic material is selected from magnesium oxide, magnesium hydroxide, barium carbonate, barium oxide, calcium oxide, or calcium hydroxide. A process as claimed in any one of the preceding claims, wherein the temperature of the mixture is from 120°C to 220°C. A process as claimed in any one of the preceding claims, wherein the heat-plastified, substantially uniform admixture is formed in at least two sequential steps comprising: (i) forming a heat-plastified, substantially uniform admixture by mixing the CPE, the plasticizing material and the basic material at a temperature sufficiently high to heat plastify the CPE with substantially no degradation thereof; and (ii) dispersing the thermoplastic polypropylene throughout the admixture while heating said admixture to a temperature above the polypropylene's crystalline melting point but below a temperature at which substantial degradation of the CPE occurs. A process as claimed in Claim 6, wherein the temperature in Step (i) is from 25°C to 150°C, and the temperature in Step (ii) is from 175°C to 220°C. A process as claimed in any one of the preceding claims, wherein the vulcanizing material comprises 2,5-dimercapto-1,3,4-thiadiazole and said activator material is selected from amines having a boiling point above 110°C and a pK value below 4.5; salts of amines having pK values below 4.5 with acids having pK values above 2.0; quaternary ammonium hydroxides and their salts with acids having pK values above 2.0; diphenyl- and ditolyl-guanidines; and the condensation products of aniline and at least one mono-aldehyde containing 1 to 7 carbon atoms in combination with at least an equal amount of an inorganic base. A process as claimed in any one of Claims 1 to 7, wherein the vulcanizing material is a derivative of 2,5-dimercapto-1,3,4-thiadiazole selected from: wherein X is a substituent selected from hydrogen, ―CRR'OH, ―(CH₂―CH―O) n H, wherein m is an integer of from 2 to 10; n is an integer from 1 to 5; R and R' are selected from hydrogen, alkyl groups containing from 1 to 8 carbon atoms, and aryl, alkaryl or aralkyl groups containing 6 to 8 carbon atoms; R² is an alkyl group containing from 1 to 17 carbon atoms, an aryl group containing 1 or 2 rings, an alkaryl group containing from 7 to 14 carbon atoms, an aralkyl group containing from 7 to 8 carbon atoms or a cyclohexyl group; and R³ is an alkyl group containing from 1 to 8 carbon atoms. X' can be the same as X with the exception of hydrogen and Y is zinc, lead, ―CRR'― , ―S― , ―SO₂― , ―SS― , wherein R⁴ is an alkylene or alkenylene group containing from 1 to 8 carbon atoms, or a cycloalkylene, arylene or alkarylene group containing from 6 to 8 carbon atoms; z is 0 or 1; and R⁵ is an alkylene group containing from 2 to 8 carbon atoms or a phenylene, methylphenylene or methylenediphenylene group. A process as claimed in any one of the preceding claims, wherein the plasticizing material is selected from trimellitate esters, phthalate esters, aromatic oils, or polyesters of dicarboxylic acid. A process as claimed in any one of the preceding claims, wherein the CPE has a weight average molecular weight of from 40,000 to 300,000, a chemically combined chlorine content of from 20 to 48 percent by weight of polymer, a 100 percent modulus (ASTM D 412) from 0.5 to 4.8 MPa, and a relative crystallinity of 0 to 15 percent. A thermoplastic elastomeric composition having a tension set value at 100 percent elongation (ASTM D 412) less than 50 percent, said composition being obtainable by the process of Claim 1 and comprising a blend of 100 pbw of an amorphous CPE, from 12 to 150 pbw of a crystalline thermoplastic polypropylene resin, and plasticizing material in an amount of from 5 to 150 pbw, the composition being processable in an internal mixer to provide a product which forms an essentially continuous sheet following transfer, with the resin components in a heat-plastified state, to the rotating rolls of a rubber mill. A composition as claimed in Claim 12, wherein the plasticizing material is selected from trimellitate esters, phthalate esters, aromatic oils, or polyesters of dicarboxylic acid. A composition as claimed in Claim 12 or Claim 13, wherein the composition includes carbon black in an amount of from 20 to 250 pbw. A composition as claimed in any one of Claims 12 to 14, wherein the amount of plasticizing material is from 30 to 250 pbw per 100 pbw of CPE present in the blend. A composition as claimed in any one of Claims 12 to 15, wherein the CPE has a molecular weight of from 40,000 to 300,000, a chemically combined chlorine content of from 20 to 48 percent by weight of polymer, a 100 percent modulus (ASTM D 412) from 0.5 to 4.8 MPa, and a relative crystallinity of 0 to 15 percent.

Inventors: AINSWORTH OLIVER C, BLANCHARD ROBERT R, FLYNN JAMES H, AINSWORTH, OLIVER C., BLANCHARD, ROBERT R., FLYNN, JAMES H.
Applicants: DOW CHEMICAL CO, THE DOW CHEMICAL COMPANY
Application year: 1989
Main classification: C08J3
IPC codes: C08K5, C08J5, C08J3, C08K3, C08L23