High temperature stable, low solvent swelling thermoplastic elastomer compositions

Abstract: Thermoplastic elastomer compositions comprise a blend of polyamide resin and a covalently-crosslinked acrylate rubber. Such compositions can be prepared by dynamic vulcanization of the rubber in admixture with the polyamide and can exhibit high temperature dimen­ sional stability and low oil swell.

Description: Disclosed herein are inventions of thermoplastic elastomer compositions which exhibit low solvent swelling at high temperatures. Particularly disclosed are inventions of thermoplastic elastomer compositions comprising polyamide and crosslinked acrylic ester copolymer rubber. BACKGROUND Unless indicated otherwise all temperatures herein are in degrees Celsius. Thermoplastics are compositions which can be molded or otherwise shaped and reprocessed at temperatures above their melting or softening point. Thermoplastic elastomers are materials which exhibit both thermoplastic and elastomeric properties, i.e. the materials can be processed as thermoplastics but have physical properties common to elastomers. Shaped articles may be formed from thermoplastic elastomers by extrusion, injection molding or compression molding without the time-consuming cure step required with conventional vulcanizates. Elimination of the time required to effect vulcanization provides significant manufacturing advantages. Further, thermoplastic elastomers can be reprocessed without the need for reclaiming and, in addition, many thermoplastic elastomers can be thermally welded. Non-polar rubbers, e.g. polybutadiene, random, graft and block copolymers of styrene and butadiene, EPDM rubber, natural rubber and polyisoprene are readily mixable with non-polar thermoplastics such as polypropylene, polyethylene and polystyrene. Non-polar, highly unsaturated rubbers are generally not used at temperatures above about 125°; and non-polar thermoplastics have low melting points, e.g. about 120° for crystalline polyethylene, about 170° for crystalline polypropylene and about 105° for polystyrene. Thermoplastic elastomers based on non-polar, unsaturated rubbers and thermoplastics generally comprise stabilizers to achieve desired properties in high temperature applications. For instance, known thermoplastic elastomers, e.g. as disclosed in U.S. Patents 4,104,210; 4,130,535 and 4,311,628, based on blends of diene or EPDM rubber and polyolefins are generally used at temperatures below about 120°. Non-polar rubbers are generally used in applications free from extended exposure to solvent-like fluids such as automotive transmission fluid, motor oil, antifreeze to avoid swelling and the possible resulting reduction in performance properties. Resistance to such swelling, especially for application temperatures below about 125°, can be achieved by use of polar rubbers, e.g. nitrile rubber, chlorinated polyethylene rubber and neoprene. Because polar rubbers are not generally miscible with non-polar thermoplastic polymers such as polypropylene, it is commonly necessary to provide compatibilization. See, for instance, U.S. Patent 4,555,546 which discloses blends of polyolefins, cured acrylic ester copolymer rubber and graft copolymer having polyolefin compatibilizing segments and rubber compatibilizing segments. Alternatively, as disclosed in U.S. Patent 4,141,863 polar rubbers can be blended with polar thermoplastics, e.g. polyamides, polyesters, polyarylates, polycarbonates. Many of the more desired polar thermoplastic polymers melt at high temperature, for instance nylon 6 melts at about 225°. Since many preferred polar rubbers may tend to degrade when melt blended for extended periods with high melt temperature polar thermoplastic, resulting thermoplastic elastomer compositions may not have optimal properties. Fortunately, certain polar acrylate rubbers are exceptionally heat stable and can be useful in blends with thermoplastics. Such rubbers include acrylic ester copolymer rubbers, including ethylene/alkyl acrylate ester copolymer rubbers and functionalized, e.g. acid-modified, derivatives thereof. See, for instance, U.S. Patents 4,310,638; 4,327,199; and 4,473,683 which disclose blends of polar thermoplastic polymers, i.e. polyamides, polyesters and styrenic polymers, respectively, with acid-containing acrylic ester copolymer rubber that is neutralized, i.e. ionically crosslinked with magnesium or zinc oxide. While such blends exhibit enhanced thermal stability, they are susceptible to solvent swelling, especially at higher temperatures where the ionic crosslink bonding becomes labile. SUMMARY OF THE INVENTION This invention provides thermoplastic elastomer compositions comprising blends of polyamide resin and covalently-crosslinked acrylate rubber. Such blends are preferably in a weight ratio of rubber to polyamide of 9:1 to 4:6. Such thermoplastic elastomer compositions exhibit excellent high temperature dimensional stability and exceptional resistance to solvent swelling. In preferred embodiments such rubber is advantageously a functionalized olefin/acrylic ester copolymer rubber that is dynamically vulcanized, e.g. by a polyfunctional, covalently crosslinking agent. In preferred embodiments the polyamide is advantageously a polycaprolactam (NYLON 6), polyhexamethyleneadipamide (NYLON 66),or mixtures or copoylmers thereof. As used herein the term "elastomeric" refers to thermoplastic compositions which exhibit rubber-like elasticity, i.e. have a tension set of less than 50 percent. DESCRIPTION OF PREFERRED EMBODIMENTS POLYAMIDE RESIN: Suitable thermoplastic polyamide resin comprises thermoplastic crystalline or amorphous high molecular weight solid polymers including homopolymers, copolymers and terpolymers having recurring amide units within the polymer chain. Both fiber forming and molding grade nylons are suitable polyamide resins. Commercially available nylons having a softening point or melting point above 100° may be advantageously used in the practice of this invention; such nylons having a softening or melting point between 160° and 280° are preferred. Examples of suitable polyamides are polylactams such as NYLON 6, polypropiolactam (NYLON 3), polyenantholactam (NYLON 7), polycapryllactam (NYLON 8) and polylauryllactam (NYLON 12); homopolymers of aminoacids such as polyaminoundecanoic acid (NYLON 11); polypyrrolidinone (NYLON 4); copolyamides of dicarboxylic acid and diamine such as NYLON 6,6, polytetramethyleneadipamide (NYLON 4,6), polytetramethyleneoxalamide (NYLON 4,2), polyhexamethyleneazelamide (NYLON 6,9), polyhexamethylenesebacamide (NYLON 6,10), polyhexamethyleneisophthalamide (NYLON 6,I) and polyhexamethylenedodecanoic acid (NYLON 6,12); aromatic and partially aromatic polyamides; copolamides such as of caprolactam and hexamethyleneadipamide (NYLON 6/6,6), or a terpolyamide, e.g. NYLON 6/6,6/6,10; block copolymers such as polyether polyamides; or mixtures thereof. Additional examples of suitable polyamides are described in the Encyclopedia of Polymer Science and Technology, Second Edition, Vol. 11, pages 315-476, incorporated herein by reference. Preferred polyamides employed in this invention are NYLON 6, NYLON 11, NYLON 12, NYLON 6,6, NYLON 6,9, NYLON 6,10, and NYLON 6/6,6. ACRYLATE RUBBER: Acrylate rubbers advantageously useful in the thermoplastic elastomer compositions of this invention comprise vulcanizable, i.e. crosslinkable, acrylate rubbers such as polyacrylate rubbers and acrylic ester copolymer rubbers. Suitable polyacrylate rubbers are described in Rubber World Blue Book, 1987 Edition, at pages 393-394, and can have functional groups, e.g. acid, hydroxy, epoxy or other functional groups, as crosslinking sites; alternatively, acid group crosslinking sites can be generated in the rubber, e.g. by partial hydrolysis of ester groups. In many embodiments olefin/acrylic ester copolymer rubbers are preferred. Such rubbers can be copolymers produced by polymerizing at least one alpha olefin with at least one C₁-C₁₈ alkyl (meth)acrylate and, optionally, a minor amount of an unsaturated functionalized monomer which can provide crosslinking sites. Such functionalized monomer can comprise acid, hydroxy, epoxy, isocyanate, amine, oxazoline, diene or other reactive groups. In the absence of such functionalized monomer, crosslinking sites can be generated, e.g. by partial hydrolysis of ester groups of the rubber. Suitable alpha olefins for polymerization of such copolymer rubbers include ethylene, propylene, butene-1, isobutylene, pentenes, heptenes and octenes or mixtures thereof; C₁-C₄ alpha olefins are preferred and ethylene is often most preferred. Suitable alkyl (meth)acrylates for copolymerizing with the alkene include methyl acrylate, ethyl acrylate, t-butyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate and n-butyl methacrylate or a mixture thereof; C₁-C₁₂ alkyl (meth)acrylates are often preferred, and C₁-C₄ alkyly (meth)acrylates are most often preferred. In many cases a preferred olefin/acrylic ester copolymer rubber comprises unsaturated carboxylic acid monomer units, e.g. derived from (meth)acrylic acid or maleic acid, anhydride units, e.g. derived from maleic anhydride or partial ester units, e.g. derived from mono ethyl maleate. In many cases a preferred olefin/acrylic ester copolymer rubber is a terpolymer of ethylene, C₁-C₄ alkyl acrylate and an acidic monomer unit; more preferably such terpolymer comprises at least about 30 mole percent of ethylene, 10 to 69.5 mole percent of methyl acrylate and 0.5 to 10 mole percent mono ethyl maleate. The acrylate rubber is essentially non-crystalline and has a glass transition temperature (T g ) below room temperature, i.e. below 23°. CROSSLINKING AGENTS: Crosslinking agents employed in the thermoplastic elastomer compositions of this invention are polyfunctional, i.e. at least difunctional, compounds selected to cure the acrylate rubber, i.e. crosslink the rubber, by covalently bonding with the reactive functional groups of the rubber. When the rubber has carboxy functional groups, e.g. derived from acrylic or maleic acid units, the covalent crosslinking agent is advantageously a compound with an hydroxy, amine, isocyanate, epoxy or other acid reactive functional group. Effective crosslinking agents include diols such as bisphenol-A, polyols such as pentaerythritol, amines such as methylene dianiline and diphenyl guanidine, isocyanates such as toluene di-isocyanate and isocyanate-terminated polyester prepolymer, epoxides such diglycidyl ether of bisphenol-A and compounds comprising more than one type of acid reactive functional group such as tris hydroxymethyl amino methane. Other covalent crosslinking agents include organic ligand complexed metals such as neoalkoxy tri[N-ethylaminoethylamino] titanite. Preferred crosslinking agents, e.g. amines, do not strongly interact with the polyamide resin. Generally, the amount of crosslinking agent does not exceed about 15 percent by weight of the acrylate rubber, depending on the molecular weight of the rubber and crosslinking agent. Preferred amounts of crosslinking agent are readily determined by routine experimentation to optimize desired properties of the thermoplastic elastomer compositions of this invention. In the case of crosslinking agents, such as isocyanates and epoxies, which can interact with the polyamide resin, it is generally desirable to use low amounts of crosslinking agent to avoid excessive crosslinking of the polyamide resin. The amount of crosslinking agent and the degree of crosslinking can be characterized in terms of the amount of rubber that is extractable from a thermoplastic elastomer composition. As used herein the term "extractable" refers to rubber that is extractable from a thermoplastic elastomer composition comprising a blend of a thermoplastic polyamide resin and a covalently-crosslinked acrylate rubber. Rubber can be extractable,e.g. because of a low level of crosslinking agent and/or because it comprises a non-crosslinkable fraction. Extractable rubber is conveniently determined by the weight loss from thin (about 0.2 mm) pressed films of thermoplastic elastomer compositions after immersion for 48 hours in a solvent (at 23°). Such solvent is selected as one in which the rubber is substantially soluble and in which the polyamide is substantially insoluble. Such solvents can include dichloromethane, toluene and tetrahydrofuran. Some preferred thermoplastic elastomer compositions will comprise sufficient crosslinking agent so that, after crosslinking, e.g. by dynamic vulcanization, no more than about 50 percent of the rubber is extractable. In other compositions, more desirable properties are achieved when not more than about 30 percent of the rubber is extractable. In still other compositions desirable properties are achieved when not more than about 20 percent of the rubber is extractable. PLASTICIZER: In certain aspects of this invention thermoplastic elastomer compositions also comprise plasticizer which extends the range of proportions of polyamide to rubber in the composition while still retaining elastomeric properties. For example, without plasticizer the weight ratio of rubber to polyamide generally cannot be less than about 4:6 without losing rubber-like elasticity; whereas, with plasticizer the weight of polyamide can be increased. Moreover, in certain preferred aspects of this invention the incorporation of plasticizers can improve the composition's resistance to oil swelling, its heat stability, and reduce hysteresis, cost and permanent set. Generally, the quantity of plasticizer, when present, is between 10 and 50 parts by weight of the composition. Suitable plasticizers are non-reactive with the polyamide resin and include phthalate esters such as dicyclohexyl phthalate, dimethyl phthalate, dioctyl phthalate, butyl benzyl phthalate and benzyl phthalate; phosphates such as tributoxyethyl phosphate, tributyl phosphate, tricresyl phosphate, cresyl diphenyl phosphate, 2-ethylhexyl diphenyl phosphate, isodecyl diphenyl phosphate and triphenyl phosphate; trimellitate esters such as C1-C9 alkyl trimellitate; sulfonamides such as N-cyclohexyl-p-toluenesulfonamide, N-ethyl-o,p-toluenesulfonamide and o-toluenesulfonamide, and liquid oligomeric plasticizers. Preferred plasticizers are liquids with low volatility to avoid emissions of plasticizer at the common melt temperatures of polyamides. The trimellitates are examples of commonly preferred plasticizers having low volatility. FILLERS: The properties of the thermoplastic elastomer compositions of this invention can be modified, by addition of fillers such as clay, silica, talc, which improve resistance to oil swelling. Such fillers are desirably incorporated into the rubber phase, especially when the polyamide is highly crystalline, to avoid imparting undue rigidity to the composition. Other ingredients can include those commonly employed in the compounding of thermoplastics and rubbers such as carbon black, titanium dioxide, pigments, zinc oxide, stearic acid, accelerators, stabilizers, antidegradants, processing aids prevulcanization inhibitors, fire retardants and coupling agents. Properties can be affected depending on when the filler is added, e.g. before or after vulcanization of the acrylate rubber. Carbon black, which can improve tensile strength, is desirably added prior to dynamic vulcanization, for instance in a masterbatch with the acrylate rubber. Stabilizers are often desirably added after dynamic vulcanization to provide lower oil swell. Desirable amounts and methods of addition of fillers, e.g. at up to about the parts by weight of rubber and polyamide, and other ingredients can be readily ascertained through routine experimentation by one skilled in the art of compounding aided by the illustrative teachings in the following examples. PREPARATION OF THERMOPLASTIC ELASTOMER COMPOSITIONS: Vulcanizable rubbers, although thermoplastic in the unvulcanized state, are often classified as thermosets because they can be cured to an unprocessable state. The improved thermoplastic elastomer compositions of this invention are processable as thermoplastics and are preferably prepared from blends of polyamide resin and vulcanizable acrylate rubber which are treated under time and temperature conditions to crosslink the rubber. Simultaneously masticating and curing such blends advantageously provides the thermoplastic compositions of this invention and avoids the production of thermosets. Thus, the thermoplastic elastomer compositions of this invention are preferably prepared by blending a mixture of vulcanizable acrylate rubber and a polyamide resin at a temperature above the melting point of the polyamide, adding crosslinking agent while continuously masticating the blend at a temperature sufficient to effect crosslink formation, using conventional masticating equipment, for example, a rubber mill, Brabender Mixer, Banbury Mixer, or a mixing extruder such as a twin screw continuous mixing extruder. The polyamide resin and vulcanizable rubber are mixed at a temperature sufficient to soften the resin or, more commonly, at temperature above the melting point of the polyamide resin. In many cases crosslinking agent is added after the molten polyamide resin and vulcanizable rubber are intimately mixed. In other cases, e.g. where a late or delayed acting curative is employed, crosslinking agent can be added prior to intimate melt mixing of the polyamide resin and rubber. Heating and masticating at vulcanization temperatures are generally adequate to complete the crosslink formation in a few minutes or less; if shorter times are desired, higher temperatures may be used. Mastication is preferably continued for a short time after the composition reaches maximum consistency, e.g. as indicated by maximum torque exerted by the mixer. Typically, mixing times of 0.5-30 minutes are satisfactory. A suitable range of temperatures for crosslink formation is from about the melting point of the polyamide resin to the decomposition temperature of the rubber which range is from 100° to 350° with the maximum temperature varying somewhat depending upon the component polyamide and rubber, the presence of antidegredants and the mixing time. Typically, the range is from 150° to 300°. A preferred range is from 180° to 280°. To obtain thermoplastic compositions, it is important that mixing continues without interruption until substantial crosslinking occurs. If appreciable crosslinking is allowed after mixing has stopped, a thermoset unprocessable composition may be obtained. A few simple experiments within the skill of practitioners in the art utilizing available polyamide resins, vulcanizable acrylate rubbers and crosslinking agents will suffice to determine their applicability for the preparation of the improved products of this invention. Methods other than dynamic vulcanization of blends of polyamide and acrylate rubber can be utilized to prepare the thermoplastic elastomer compositions of this invention. For example, the rubber can be fully vulcanized in the absence of the polyamide resin, either dynamically or statically, powdered, and mixed with the resin at a temperature above the melting or softening point of the polyamide resin. Provided that the crosslinked rubber particles are small, e.g. not greater than about 50 micrometers (microns), well dispersed and in an appropriate concentration, the compositions of this invention are attainable by blending crosslinked rubber with polyamide resin. A mixture which is outside the invention because it contains poorly dispersed or too large rubber particles can be comminuted by cold milling to reduce the weight average particle size to below 50 microns, preferably to below 20 microns, more preferably to below 10 microns and even more preferably to below 5 microns. After sufficient comminution or pulverization, a composition of this invention can be obtained. Frequently, a composition of poor dispersion or too large particle size is visibly obvious to the naked eye and observable in a molded sheet, especially in the absence of pigments and fillers; such compositions are outside the scope of this invention. The characteristics of the thermoplastic elastomer compositions containing cured acrylate rubber depend upon the relative proportions of rubber and polyamide and whether the compositions are statically or dynamically cured. Static curing can give thermoset compositions when the blend contains more than 30 parts of cured acrylate rubber per 100 parts by weight of rubber and polyamide; whereas, dynamic curing of blends containing even up to 90 parts by of cured acrylate rubber per 100 parts of rubber and polyamide generally provides thermoplastic compositions. When such high rubber compositions are partially crosslinked the rubber and polyamide can comprise co-continuous phases. Generally, compositions comprising about 40 parts or more of cured acrylate rubber per 100 parts of rubber and polyamide are thermoplastic and elastomeric. Moreover, unplasticized compositions comprising less than about 35 parts of cured acrylate rubber per 100 parts rubber and polyamide can be considered to be toughened thermoplastics. The effect of the relative proportions on blend composition characteristics cannot be defined with precision because the limits vary depending upon a number of factors, such as, the kind of polyamide and acrylate rubber, the presence of fillers, plasticizers and other ingredients, and the extent the rubber is cured. Of course, it is understood that the properties of the compositions of the invention may be modified by the addition of ingredients which are conventional in the compounding of polyamides, acrylate rubbers, and blends thereof. For additional information concerning compounding and dynamic vulcanization, refer to U. S. Patents 4,104,210; 4,130,535 and 4,141,863, all of which are incorporated herein by reference. The term "blend" as used herein means a mixture ranging from small particles of crosslinked rubber well dispersed in a polyamide matrix to co-continuous phases of polyamide and a partially- crosslinked rubber. Compositions prepared by dynamic vulcanization comprising a blend of polyamide, e.g. NYLON 6, and cured acrylate rubber, e.g. acrylic ester copolymer rubber, in the form of small particles dispersed throughout the polyamide are preferred. Especially preferred are such compositions comprising such rubber and polyamide in the range of 20 to 60 parts of polyamide per 100 parts of rubber and polyamide, more preferably less than about 55 parts of polyamide. Thermoplastic elastomer compositions of this invention can be used to form a variety of molded, extruded, or calendered articles. The properties of such compositions depend upon the proportions of the components with a wide range of properties being available simply by varying such proportions. The following disclosure is provided to illustrate specific embodiments and aspects of thermoplastic elastomer compositions of this invention. The tensile properties of such compositions was determined in accordance with ASTM procedure D 638. Unless otherwise indicated specimens were pulled in a tensile tester at 50.8 cm. (20 inches) per minute to failure. Ultimate tensile stress (UTS) is the tensile strength at break and is reported in units of megaPascals (MPa). Tensile modulus at 100 percent elongation (M100) and tensile modulus at 300 percent elongation (M300) are reported in MPa. Ultimate elongation (UE) is the elongation at break and is reported as a percent of the original specimen length. Hardness (H) is reported as a Shore A hardness (A) or a Shore D hardness (D). Tension set (TS) is the extension remaining after a specimen has been stretched and held for 10 minutes at twice its original length, then allowed to retract; TS is measured as the percentage increase of the original length after 10 minutes of retraction. Oil swell (OS) is determined in accordance with ASTM procedure D 471; OS is the measured increase in specimen mass after immersion in hot oil, expressed as a percentage of original mass. Unless otherwise indicated, e.g. by a temperature in parentheses or otherwise, specimens were immersed for 70 hours in ASTM Reference Oil No. 3 at 150°. Low temperature brittle point (LTB) is determined in accordance with ASTM procedure D 746; LTB is the temperature at which the specimen fractured by brittle failure upon impact, reported in degrees Celsius. Materials used in the following examples include: Polyamides: PA-1: Capron 8202NL NYLON 6 from Allied-Signal; PA-1C: Capron 8202C NYLON 6 from Allied-Signal; PA-2: Rilsan BMNO NYLON 11 from Rilsan Corp.; PA-3: Grilamid L20G NYLON 12 from Emser Industries; PA-4: Zytel 101 NYLON 6,6 from DuPont; PA-5: Vydyne 60H NYLON 6,9 from Monsanto; PA-6: NYLON 6/6,6 (mp: 213°) PA-7: Elvamide 8064 NYLON 6/6,6/6,10 from DuPont; PA-8: Zytel 109L NYLON polymer from DuPont; and PA-9: Rilsan 6312 nylon block copolyester from Rilsan Corp. Acrylate Rubbers: R-1: VAMAC-G neat terpolymer of about 73 mole percent of ethylene, about 26 mole percent of methyl acrylate and about one mole percent of carboxylic acid from DuPont; R-2: VAMAC-123 masterbatch of 100 parts of VAMAC-G 20 parts of fumed silica and 3 parts of stabilizers and processing aids. Crosslinking agents: XL-1: tris(hydroxymethyl)amino methane from Angus Chemical Company; XL-2: LICA-44 neoalkoxy tri[N-ethylaminoethylamino] titanite from Kenrich Petrochemical; XL-3: 4,4'-methylene dianiline from Olin Chemicals; XL-4: 4,4'-methylenebis(cyclohexylamine) from Aldrich Chemical Company; XL-5: N-(2-aminoethyl)-piperazine from Aldrich Chemical Company; XL-6: Maglite D magnesium oxide from Merck; XL-7: Mondur E-501 isocyanate-terminated polyester prepolymer from Mobay, about 19 percent NCO. Stabilizers: S-1: mixture of 0.4 pbw Irganox MD 1024 and 0.3 pbw Chimassorb 944LD and 0.2 pbw Irganox 1425 antioxidants from Ciba-Geigy; S-2: mixture of 0.4 pbw Ethanox 330 from Ethyl Corp., 0.3 pbw calcium stearate, and 0.2 pbw Carbstab distearylthiodipropionate from Cincinnati Milacron. Processing aids: MgS: Magnesium stearate; ZUN: Zelec UN unneutralized alcohol phosphate lubricant from DuPont; and SAM: Bis(t-butylaminocyclohexyl)methane. Fillers: F-1: Novakup L207A silica from Malvern Minerals; F-2: Burgess 2211 clay from Burgess Pigment Co.; and F-3: Stan-White 500 calcium carbonate from Hardwick. Plasticizers: P-1: Santicizer 79-TM alkyl trimellitate plasticizer from Monsanto Chemical Company; P-2: Santicizer 9 ortho, para-toluene sulfonamide plasticizer from Monsanto Chemical Company; P-3 Santicizer 148 isodecyl diphenyl phosphate plasticizer from Monsanto Chemical Company. EXAMPLE 1 This example serves to illustrate thermoplastic elastomer compositions of this invention comprising polyamide PA-1, acrylic ester copolymer rubber R-1 and varying amounts of tris(hydroxymethyl) amino methane crosslinking agent XL-1. Controlling the degree of crosslinking, indicated by the amount of the composition, e.g. rubber, extractable in a solvent affords tailoring compositions to achieve a desired balance of properties. Compositions according to this invention comprising tris(hydroxymethyl)amino methane crosslinking agent were prepared by melt mixing the polyamide PA-1 and rubber R-1 (containing 0.9 parts stabilizer S-1 per 100 parts rubber) at 100 rpm and 240° in a Brabender mixer; after 3 minutes crosslinking agent XL-1 was added to the blends which were dynamically vulcanized by continued mixing for an additional 3-4 minutes after maximum consistency was reached; the blend stocks were removed, cooled then returned to the Brabender for an additional 1-2 minutes of mixing; then the stocks were cooled and compression molded at 250°. Tensile properties of specimens are evaluated on a T-500 Tensometer at a speed of 20 inches (50.8 cm) per minute. The degree of crosslinking is determined from pressed films of each composition. Films, about 0.2 mm thick, were immersed in dichloromethane at about 23° for about 48 hours. The weight loss of the composition is divided by the weight of original rubber in the composition to determine extractable rubber (Extract). The analytical results indicate that compositions having not more than about 30 percent extractable rubber are sufficiently highly crosslinked to provide thermoplastic elastomer compositions of preferred properties. EXAMPLE 2 This example serves to illustrate thermoplastic elastomer compositions of this invention over a range of rubber levels, e.g. with a rubber to polyamide ratio from 9:1 to 4:6, having enhanced properties, e.g. UTS, UE, H, TS and/or OS, as compared to prior art compositions comprising no crosslinking agent or ionomeric crosslinking agent such as magnesium oxide. Prior art compositions without crosslinking agent were prepared by melt mixing polyamide PA-1 and acrylic ester copolymer rubber R-1 containing 0.81 parts stabilizer S-2 per 100 parts rubber at 100 rpm and 240° for 10 minutes in a Brabender mixer; the blend stocks were removed, cooled then returned to the mixer and remixed for one additional minute; then the blend stocks were removed and compression molded at 250°. Prior art compositions comprising ionomeric crosslinking agents were prepared by melt mixing the polyamide and rubber at 100 rpm and 240° in a Brabender mixer; after 2 minutes magnesium oxide, crosslinking agent, XL-6 and magnesium stearate were added to the blends which were dynamically vulcanized by continued mixing for an additional 10 minutes or until 3 minutes after maximum consistency is reached; then the stocks were cooled, remixed for 1-2 minutes and then compression molded at 280°. Compositions according to this invention comprising tris(hydroxymethyl)amino methane, crosslinking agent XL-1, were prepared by melt mixing the polyamide and rubber at 100 rpm and 240° in a Brabender mixer; after 3 minutes the crosslinking agent XL-1 was added to the blends which were dynamically vulcanized by continued mixing for an additional 3-4 minutes after maximum consistency was reached; the blend stocks were removed, cooled then returned to the Brabender for an additional 1-2 minutes of mixing; then the stocks were cooled and compression molded at 250°. Tensile properties of specimens are evaluated on a T-500 Tensometer at a speed of 20 inches (50.8 cm) per minute. The data shows that tensile properties are improved by vulcanization. The data also shows that properties are enhanced by use of a covalently crosslinking agent as compared to an ionomeric crosslinking agent. For instance, lower hardness, often with lower oil swell can be provided in compositions having a rubber:polyamide ratio of 9:1; lower hardness can be provided in compositions having a rubber: polyamide ratio of 8:2; lower oil swell and tension set can be provided in compositions having a rubber: polyamide ratio of 8:2 or less; and higher tensile properties can be provided in compositions having a rubber:polyamide ratio of 4:6 or less. R-1 90 90 90 90 90 PA-1 10 10 10 10 10 XL-1 0 0 0.36 0.54 0.72 XL-6 0 0.9 0 0 0 MgS 0 0.45 0 0 0 S-2 0.81 0.81 0.81 0.81 0.81 UTS 0.3 11 6.7 7.2 7.9 M100 0.3 1.6 0.8 1.3 1.8 UE 370 640 580 230 200 H 18A 44A 32A 36A 36A TS 40 3 6 4 2 OS(125) * 94 90 78 61 OS(150) * 137 125 97 90 OS(175) * 153 179 117 100 Extract 101 16 33 15 14 *disintegrated R-1 80 80 80 80 80 PA-2 20 20 20 20 20 XL-1 0 0 0.48 0.64 0.8 XL-6 0 0.8 0 0 0 MgS 0 0.4 0 0 0 S-2 0.72 0.72 0.72 0.72 0.72 UTS 0.3 14 7.3 8.2 8.2 M100 0.3 5.7 2.2 3.7 4.1 UE 430 450 260 190 180 H 22A 62A 44A 48A 51A TS 40 6 2 2 2 OS(125) * 78 72 66 57 OS(150) * 99 91 81 72 OS(175) * 118 109 96 86 Extract 100 13 19 13 12 *disintegrated R-1 70 70 70 70 70 PA-2 30 30 30 30 30 XL-1 0 0 0.56 0.7 0.84 XL-6 0 1.4 0 0 0 MgS 0 0.35 0 0 0 S-2 0.63 0.63 0.63 0.63 0.63 UTS 0.3 22 11 13 14 M100 0.4 14 5.2 6.4 8.1 UE 420 290 200 200 170 H 28A 82A 63A 70A 90A TS 43 16 5 7 8 OS(125) * 47 46 45 43 OS(150) * 60 59 53 51 OS(175) * 68 64 63 62 Extract 100 6.5 16 11 11 *disintegrated R-1 60 60 60 60 PA-2 40 40 40 40 XL-1 0 0 0.72 1.08 XL-6 0 1.2 0 0 MgS 0 0.3 0 0 S-2 0.54 0.54 0.54 0.54 UTS 0.2 27 24 27 M100 0.6 19 14 16 UE 2500 320 240 240 H 38A 45D 40D 44D TS 47 40 31 36 OS(125) * 39 25 23 OS(150) * 46 29 26 OS(175) * 54 37 31 Extract 97 6.4 10 8 *disintegrated R-1 50 50 50 50 PA-2 50 50 50 50 XL-1 0 0 0.75 0.9 XL-6 0 1 0 0 MgS 0 0.25 0 0 S-2 0.45 0.45 0.45 0.45 UTS 2.7 32 29 28 M100 2.4 24 18 17 UE 140 320 260 250 H 72A 61D 52D 49D TS -- 65 49 47 OS(125) * 18 17 17 OS(150) * 29 18 20 OS(175) * 36 23 24 Extract 95 6.3 10 9 *disintegrated R-1 40 40 40 40 PA-2 60 60 60 60 XL-1 0 0 0.6 0.72 XL-6 0 0.8 0 0 MgS 0 0.2 0 0 S-2 0.36 0.36 0.36 0.36 UTS 4.8 32 39 38 M100 4.8 32 28 28 UE 100 140 300 260 H 85A 67D 62D 64D TS -- 75 70 67 OS(125) * 9 4 4 OS(150) * 13 5 5 OS(175) * 19 7 8 *disintegrated EXAMPLE 3 This example serves to illustrate thermoplastic elastomer compositions based on a variety of polyamides, including NYLON 6, NYLON 11, NYLON 12, NYLON 6,6, NYLON 6,9, the mixed polyamides PA-6, PA-7 and PA-8, and block polyether-polyamide PA-9. The polyamides were combined with acrylic ester copolymer rubber R-1 and tris(hydroxymethyl)amino methane, crosslinking agent, X-1, in the proportions specified in Table 3 essentially in the manner of Examples 1 and 2. The analytical results reported in Table 3 indicate that thermoplastic elastomer compositions according to this invention can be prepared from a variety of polyamides. R-1 60 60 60 60 60 60 60 60 60 PA-1 40 0 0 0 0 0 0 0 0 PA-2 0 40 0 0 0 0 0 0 0 PA-3 0 0 40 0 0 0 0 0 0 PA-4 0 0 0 40 0 0 0 0 0 PA-5 0 0 0 0 40 0 0 0 0 PA-6 0 0 0 0 0 40 0 0 0 PA-7 0 0 0 0 0 0 40 0 0 PA-8 0 0 0 0 0 0 0 40 0 PA-9 0 0 0 0 0 0 0 0 40 XL-1 1.05 1.05 1.05 1.05 1.05 1.05 1.05 1.05 1.05 S-1 0.54 0.54 0.54 0.54 0.54 0.54 0.54 0.54 0.54 UTS 29 22 22 24 23 23 25 24 24 M100 19 12 13 17 13 12 9 17 9 UE 260 350 270 180 280 250 320 210 330 H 48D 42D 48D 45D 43D 39D 91A 44D 88A TS 45 50 48 28 42 28 16 25 16 OS(125) 23 21 25 22 21 25 23 22 30 OS(150) 25 30 33 25 26 29 40 29 34 OS(175) 34 61 64 26 46 47 82 33 50 EXAMPLE 4 This example serves to further illustrate thermoplastic elastomer compositions which have been dynamically vulcanized with one of a variety of covalently crosslinking agents. Such compositions exhibit enhanced resistance to oil swell as compared to compositions dynamically vulcanized with ionically crosslinking agents. The compositions were prepared essentially in the manner of Examples 1 and 2. The analytical results reported in Table 4 indicate that a variety of covalently crosslinking agents can be used to provide thermoplastic elastomer compositions with higher tensile properties and higher resistance to oil swell. R-1 60 60 60 60 60 60 PA-1C 40 40 40 40 40 40 XL-2 0 1.05 0 0 0 0 XL-3 0 0 1.05 0 0 0 XL-4 0 0 0 0.75 0 0 XL-5 0 0 0 0 0.75 0 XL-6 0 0 0 0 0 1.2 MgS 0 0 0 0 0 0.3 SAM 0 0 0.15 0 0 0 ZUN 0 0 0.3 0.3 0 0 S-1 0 0 0.54 0 0 0 S-2 0.54 0.54 0 0.54 0.54 0.54 UTS 0.3 26 26 21 24 20 M100 0.4 18 18 17 16 15 UE 1870 220 200 170 260 230 H 36A 45D 42D 35D 37D 87A TS 55 39 35 33 36 27 OS(125) * 24 22 37 30 44 OS(150) * 28 26 39 35 51 OS(175) * 35 32 44 44 64 Extract 96 8 7 15 11 10 *Disintegrated EXAMPLE 5 This example serves to illustrate thermoplastic elastomer composition dynamically vulcanized with covalently crosslinking agents comprising isocyanate-terminated polyester prepolymer. Such compositions are especially soft and can exhibit low tension set and enhanced resistance to oil swell at high temperatures. The compositions were prepared essentially in the manner of Examples 1 and 2 in the proportion of components set forth in Table 5. The results of analyses indicate that unneutralized alcohol phosphate can be used to promote enhanced crosslinking and lower oil swell. R-1 60 60 60 60 60 60 60 60 PA-1C 40 40 40 40 40 40 40 40 XL-7 0 1.2 1.2 1.2 3 3 3 3 ZUN 0 0 0 0.3 0 0 0.3 0.15 MgS 0 0 0.3 0 0 0.3 0 0.15 S-2 0.54 0.54 0.54 0.54 0.54 0.54 0.54 0.54 UTS 0.3 5.8 7.0 16 21 10 26 20 M100 0.4 2.4 4.6 6.4 13 10 18 17 UE 1870 450 220 240 190 100 200 140 H 36A 55A 64A 65A 77A 78A 90A 77A TS 55 10 16 3 12 Failed 21 13 OS(125) * 64 57 61 48 43 35 46 OS(150) * 78 64 72 52 47 38 49 OS(175) * 84 67 82 62 49 44 56 Extract 96 55 49 30 16 23 11 17 *Disintegrated EXAMPLE 6 This example serves to illustrate thermoplastic elastomer compositions comprising a variety of fillers. The compositions were prepared from components in the proportions set forth in Table 6 essentially in the manner of Example 1 except that fillers and stabilizers were preblended with the rubber to form a masterbatch. In the case of R-2, the rubber is provided as a masterbatch. The results of analyses indicate that fillers can be used to provide compositions of this invention with desired properties such as low oil swell. R-1 60 60 60 -- R-2 -- -- -- 73.8 PA-1 40 40 40 40 XL-1 1.2 1.2 1.2 -- XL-3 -- -- -- 1.2 S-2 0.54 0.54 0.54 -- F-1 12 -- -- -- F-2 -- -- 12 -- F-3 -- 12 -- -- UTS 24 25 25 29 M100 18 18 20 21 UE 180 190 190 180 H 46D 45D 48D 42D TS 37 32 37 31 OS(125) 21 24 21 20 OS(150) 24 28 25 22 OS(175) 32 35 31 27 EXAMPLE 7 This example serves to illustrate thermoplastic elastomer compositions comprising a variety of plasticizers. The compositions were prepared from components in the proportions set forth in Table 7 essentially in the manner of Example 1 except that plasticizer was added to the blend with the polyamide. The results of analyses indicate that plasticizers can be effective in providing compositions with exceptionally low oil swell even at elevated temperatures. R-2 73.8 73.8 73.8 73.8 73.8 73.8 PA-1 40 40 40 40 40 40 XL-1 1.2 1.2 1.2 1.2 1.2 1.2 P-1 0 10 20 0 0 0 P-2 0 10 20 20 40 0 P-3 0 0 0 0 0 20 UTS 26 20 16 22 22 20 M100 22 15 12 16 10 14 UE 220 170 180 220 260 170 H 43D 37D 90A 39D 90A 72A TS 40 25 20 25 20 21 OS(125) 21 15 6 15 6 16 OS(150) 24 18 7 17 6 19 OS(175) 29 23 13 22 11 26 COMPARATIVE EXAMPLE This example serves to further illustrate thermoplastic elastomer compositions dynamically vulcanized with ionically crosslinking agent XL-6, magnesium oxide, exhibit higher oil swell and may tend to disintegrate in oil at higher temperatures. The compositions were prepared essentially in the manner of Example 1 in the proportion of components set forth in Table 8. R-1 60 60 60 60 60 60 60 PA-1 40 40 40 40 40 40 40 XL-6 0 0.3 0.6 0.9 1.2 1.5 1.8 MgS 0.3 0.3 0.3 0.3 0.3 0.3 0.3 S-1 0.54 0.54 0.54 0.54 0.54 0.54 0.54 UTS 0.34 6.8 11 18 20 24 26 M100 0.83 2.5 6.9 14 15 17 19 UE 2320 400 290 280 290 300 300 H 42A 57A 70A 40D 42D 40D 40D TS 40 10 12 44 40 27 32 OS (125) * 61 55 47 42 38 38 OS (150) * 79 69 55 49 44 43 OS (175) * * * 58 55 50 51 Extract 95 45 29 8 8 8 7 *Distintegrated

Claims: A thermoplastic elastomer composition comprising a blend of a thermoplastic polyamide resin and a covalently-crosslinked, acrylate rubber, which rubber prior to crosslinking is non-crystalline and has a glass transition temperature below 23°C, wherein the polyamide resin is not significantly crosslinked and wherein the elastomer has a tension set of less than 50 percent''. A composition according to Claim 1, wherein said polyamide comprises nylon 6, nylon 6,6 or a mixture or copolymer thereof. A composition according to Claim 1, wherein said polyamide comprises nylon 66. A composition according to Claim 1, wherein said polyamide comprises nylon 6. A composition according to any of the preceding claims, wherein no more than 50 percent of said rubber is extractable. A composition according to Claim 5, wherein no more than 30 percent of said rubber is extractable. A composition according to Claim 5, wherein no more than 20 percent of said rubber is extractable. A composition according to any of the preceding claims, wherein said rubber is a polyacrylate rubber with acid, hydroxy or epoxy groups as crosslinking sites. A composition according to any of the preceding claims, wherein said acrylate rubber is an olefin/acrylic ester copolymer rubber. A composition according to any of Claims 1 to 7, wherein said rubber is a covalently-crosslinked, acid-containing, acrylic ester/olefin copolymer rubber. A composition according to Claim 10, wherein said rubber contains carboxylic acid monomer units. A composition according to any of the preceding claims, wherein said copolymer rubber is covalently crosslinked by a polyamine. A composition according to any of the preceding claims, wherein said rubber comprises a copolymer of ethylene, alkyl acrylate and unsaturated carboxylic acid. A composition according to any of the preceding claims, wherein said composition comprises 10 to 60 parts of said polyamide per 100 parts of rubber and polyamide. A composition according to Claim 14, wherein said composition comprises less than 55 parts of polyamide per 100 parts of rubber and polyamide. A composition according to any of the preceding claims, further comprising particulate filler. A composition according to any of the preceding claims, further comprising plasticizer at up to 50 percent by weight of the composition.

Inventors: PATEL RAMAN, PATEL, RAMAN
Applicants: ADVANCED ELASTOMER SYSTEMS, ADVANCED ELASTOMER SYSTEMS, L.P.
Application year: 1989
Main classification: C08L23
IPC codes: C08L77, C08L33, C08L23, C08J3