FLUORINATED THERMOPLASTIC ELASTOMER COMPOSITIONS

Abstract: A two-phase fluorocarbon composition in which the continuous phase is a crystalline thermoplastic, and the discontinuous phase is a crosslinked elastomer. The disper­ sal phase constitutes 50 to 90% of the total. The composition is prepared by dynamic curing.

Description: TITLE PLL1ORINATED THERMOPLASTIC ELASTOMER COMPOSITIONS FIELD OF THE INVENTION This invention relates to fluorinated thermoplastic elastomer compositions which contain two phases, namely a continuous fluorinated crystalline thermoplastic phase and a disperses fluorinated amorphous elastomeric phase. The compositions nay be produced by melt blending the fluorinated thermoplastic and an uncured iiuorinatea amorphous elastomeric polymer, and then dynamically curing the uncured fluorinated polymer to form elastomeric particles which are dispersed in the fluorinated thermoplastic. The compositions may also be produced by latex blending. The compositions of this invention have the highly desirable property of low compression set, that is when articles maae of the composition are compressed for long perioas of time even at high temperatures they have a strong tendency to return to their original size and shape. Another advantage of the compositions of the invention is that flash, or defective parts can be reprocessed without difficulty. BACKGROUND OF THE INVENTION Two-phase compositions of a continuous phase thermoplastic polymer and dispersed phase elastomer produced by dynamically curing the elastomer while it is dispersed in the thermoplastic are known. See for example, Coran et al. U.S. Patents 4,348,502, 4,130,535, 4,173,556, 4,207,404 and 4,409,365. Fluorinated and partially fluorinated crystalline thermoplastics are high volume commercial products. Such plastics often contain large amounts of the polymerized monomer, tetrafluoroethylene. Likewise, fluorinated and partially fluorinated amorphous elastomers are known high volume commercial products. Such elastomers induce the cured (vulcanized or crosslinked) copolymers of vinylidene fluoride with hexafluoropropylene and the like. SUMMARY OF THE INVENTION The present invention in a two-phase composition having a continuous phase consisting essentially of a crystalline thermoplastic fluorocarbon resin, and a dispersed phase which consists essentially of an amorphous cured (crosslinkea or vulcanized) fluoroelastomer. The dispersed phase constitutes 50 to 90 percent by weight of the two phase composition. The two-phase composition of the invention may be prepared by the process of the invention. Trite process of the invention comprises melt blending tne thermoplastic crystalline fluorocarbon resin, ana the uncured amorphous fluoroelastomer, at a temperature above the crystalline melting point of the resin, ana then dynamically curing the elastomer. "Dynamically curing" means curing while the blena is undergoing mixing, stirring and shear. The curing is carried out by introducing one or more curing agents or free radical sources to the melt blend, and maintaining the temperature at a high enough level that the elastomer crosslinks. The compositions of this invention may be chopped into injection molding granules, and injection molded in a conventional injection molding machine. The compositions can also be compression molded, or extrusion molded. DETAILED DESCRIPTION The thermoplastic crystalline fluorocarton resins useful in compositions of the present invention must be "melt-processable". By "melt-processable" we mean a polymer whose melt flow can be measured in an extrusion plastometer VAST D-1238, D-2l16) at a temperature above the crystalline melting point of the polymer. Polytetrafluoroethylene cannot be processed by the usual methods of thermoplastic fabrication because of its viscoelastic properties, as describe in ASTM D-1457. Polytetrafluoroethylene is not melt-processable. Generally, the thermoplastic crystalline fluorocarbon resin will contain a minimum of 38 percent by weight fluorine. Further the thermoplastic crystalline fluorocarbon resin should be melt-processable at a temperature below tnat at which degradation of the amorphous fluorocarbon elastomer occurs to any significant degree. The thermoplastic crystalline fluorocarbon resins useful in the compositions of this invention include (a) copolymers of tetrafluoroethylene and ethylene, copolymers of tetrafluoroethylene and hexafluoropropylene, copolymers of tetrafluoroethylene and perfluoro(propyl vinyl ether) and copolymers of tetrafluoroethylene and perfluorobutyl ethylene, (b) homopolymers of vinylidene fluoride as well as copolymers of vinylidene fluoride in which the vinylidene fluoride is the greatly predominant polymerized monomer, (c) copolymers of chlorotrifluoroethylene with ethylene or halogenated monomers. Such polymers are well known in the art and many are commercially available. The elastomeric components of the compositions of this invention are also well known in the art and most are commercially available. Suitable elastomeric components include, copolymers of vinylidene fluoride and hexafluoropropylene, terpolymers of tetrafluoropropylene, vinylidene fluoride and hexafluoropropylene, terpolymers of hexafluoropropylene, vinylidene fluoride and bromotetrafluorobutene-l, polymers of tetrafluoroethylene, vinylidene fluoride, hexafluoropropylene, bromotetrafluorobutene-l, and trimethylallylisocyanurate, also known as 1,3,5-trimethallyl-1,3,5-triazine-2,4,6-(-H, 3H, 5H)-trione; terpolymers of hexafluoropropylene, vinylidene fluoride and iodotetrafluorobutene-l, ana terpolymers of tetrafluoroethylene perfluoromethyl perfluorovinyl ether and EMI4.1 Such elastomers usually haVe molecular weights (prior to curing) such that they have a Mooney viscosity of about 30 to 200 tML-10 at 1000C]. The elastomeric component of the composition of the present invention generally will contain a minimum of 58 percent by weight fluorine. The elastomer phase of the composition of the invention may be cured with conventional curing systems known for curing fluoroelastomers, such as combinations of (a) magnesium oxide, Bisphenol AF and organophosphonium salts; (b) magnesium oxide, the dipotassium salt of Bisphenol AF and dicyclohexyl 18 Crown 6 (c) 2,5,dimethyl-2,5-ditertbutylperoxyhexyne-3 (sold as Luperco 13ú XL--45% active ingredient on a solid support) with meta phenylenebismaleimide or triallyl isocyanurate, (d) cumene hydroperoxide and maleimide or l,3,5-triallyl-1,3,5- triazine-2,4,6-(lH,3H,5H)-trione; also known as triallyl isocyanurate. The compositions of the invention contain about 50 to 90 percent by weight of the cured elastomeric component, preferably about o0 to 80 percent by weight, the remaining portion of the composition being the thermoplastic crystalline fluorocarbon resin. The composition of the invention may contain fillers, antioxidants, stabilizers, pigments, processing aids, and the like in amounts conventionally added to fluorocarbon thermoplastics of the art. The particle size of dispersed phase of the compositions of the invention covers a wioe range, and depends among other things on the processing conditions under which the compositions were prepared, the amount of each component in the compositions, the viscosity of each component in the composition. In general more desirable physical properties are obtained with tne compositions of tne invention having greater than 50 percent of the weight of the elastomeric particles smaller than about 3 micrometers. A preferred method of preparing the compositions of the invention is by mixing the components in a extruder or mixer at a temperature above the crystalline melting point of the crystalline component, and then adding the curing agent while continuing the mixing. The temperature of the mixture after the addition of the curing agent may be increased to speed up the reaction. The mixture may be removed from the mixing device prior to completion of the curing reaction if desired, provided the temperature is maintained at a level sufficiently thigh to complete the curing reactions. The mixing of the components is best carriea out at temperatures above about 2000C, ana the curing is best carried out at above about 2500C. The compositions of the invention may also be prepared by mixing a latex of the elastomeric component containing the selected curing agent with a suspension of the thermoplastic component. The polymer suspension is then filtered out dried and cured. The curing may take place during molding if desired. In the following examples which illustrate the invention, all parts and percentages are by weight unless otherwise specified. Examples 1-9 Details of formulations and properties are provided in Table 1. Procedure for Examples 1 to 7 The amorphous elastomer (designatea 1 in Table 1) employed was a commercial high viscosity copolymer of vinylidene fluoride, 60%, and hexafluoropropylene 40%. The elastomer was charged to Brabender Plastograph at about 2000, 40 rpm rotor speed and masticated while the thermoplastic resin was added at 200-2500C. The temperature was then raised to 290-320 C, under nitrogen, and mastication continued at 90 rpm until an unicorn melt was obtained. The temperature was then droppea to 2900C, while fillers (if any) and curing agents were added in the order listed in Table I. Mastication was continued at 2900-3000C for 15 mins. after te last ingredient was added. In Examples 2, 3, 5 ana 7 the products became powder on the addition of magnesium oxide. The product was then removed from the mixer and placed in a tray for transfer to an air oven whereon it was heated at 2350 to-245 C for 16 hours. The product could then be compression molded at about 3250C into slabs from which specimens were die-cut for tensile and compression set tests. Tensile tests were run at 2" per minute, 20 C (ASTM D638-77). Compression set conditions were 22 hours at 1500C, except for example 5 which was run at 1000C (ASTM D395, Type 2). In the melt flow test, the melt indexer temperature was 3650C and 5 minute cuts were taken. Flow rates were reported in grams/10 mins using a 10 Kg weight (ASTM 1238-73). Procedure for Examples 8 and 9. The procedure for Examples 6 ana 9 was similar to Examples 1 to 7 except that the curing was at 2200C, and the products were not heated during preparation above 2500C. TABLE I COMPOSITIONS CURED BY MgO-CURATIVES SYSTEM Example 1 2 3 4 5 6 7 8 9 Amorphous elastaner 70 70 70 70 70 70 70 70 70 *Thermoplastic 1 30 20 20 20 n 2 30 10 10 3 3 30 10 n 4 30 5 30 6 30 ** Filler 1 1.5 0.5 2 2 0.5 0.5 *** Curing Agent 1 2 2 2 2 2 2 2 2 2 N " 2 3 2 2 2 2 2 2 2 2 2 Mg 0 3 3 2 2 2 3 2 2 2 Shore A 83 75 78 82 76 77 85 90 88 TB (MPa) 12.55 3.65 9.03 7.31 3.58 7.45 3.8614.07 3.1 TB (psi) 1820 530 1310 1060 520 1080 560 2040 450 Elongation % 250 170 300 170 160 230 100 160 170 Comp. Set at 150 C 0 32 4 2 10 0 49 11 0 Melt Elow at 365 C 0.88 30 0.7 0.5 0.3 0.22 1.8 No flow at (g/10 min) 2600 *Thermoplastic 1 77.6% tetrafluoroethylene, 3.4% perfluorobutyl ethylene, 19% ethylene 2 2 84% tetrafluoroethylene, 13% @exafluoropropylene " 3 97% tetrafluoroethylene, 3% perfluoropropylvinylether 4 95% tetrafluoroethylene, 5% perfluorobutyl ethylene 5 5 Polyvlnylidene fluoride 6 6 80% chlorotrifluoroethylene, 20% ethylene ** Filler 1 medium thermal carbon black 2 2 Po lytetrafluoroethy lene Powder *** Curing Agent 1 33% benzyl triphenyl phosphonium chlorioe + 64% copolymer of 60% vinylidene fluoride ana 40% hexafluoropropylene " 2 50% Bisphenol AF + 50% copolymer of 60% vinylidene fluoride and 40% hexafluoropropylene Examples 10-17 Procedure The elastomer and the resin were masticated as in Examples 1-9 before adding the curatives at 90 rpm. The blend was cooled to 240-2500C before adding the curatives, and temperature taken back up to 3000C during the 15 minutes cure period. All samples were heated at 2450C for 16 hours to complete curing. Examples 10-17 in Table II illustrate embodiments wherein a desirable combination of melt flow, tensile strength and some significant degree of recovery from compression at 100 C was achieved. In the peroxide crosslinked systems, a substantial content of a gel polymer such as thermoplastic B (Table II), appears to be highly aesirable to obtain good compression set. Oil swell tests were carried out on the product of Example 16 at 1500C for 70 hours. The swell values were 0.68 in ASTM &num;2 oii and 9.4% in DOT 4 Brake Fluid. Example 17 was run twice and the products converted to molding powder of 1/8" size by molding into thick slabs and hand cutting. The molding powder, after dry blending, was fed to a 1" plunger type molding machine with cylinder and nozzle temperatures at 3500C. Various objects incluaing discs, bars and pocket combs were molded by injecting the melt into unheated V-block molds. Good mola filling was demonstratea. Trite aiscs were converted into seals by cutting appropriate sized holes. TABLE II COMPOSITIONS CURED BY PEROXIDE Example 10 11 12 13 14 15 16 17 *Amorphous elastomer 2 35 40 50 40 35 35 35 " 3 35 40 30 40 35 35 35 " 4 70 **Thermoplastic 7 30 20 30 10 30 30 30 " 8 20 9 9 30 ***Filler 1 1.4 1.6 1.6 1.0 1.4 0.5 n ;g 0.5 ****Curing Agent 3 2 2 2 2 2 2 2 2 " " 4 2 " " 5 3 3 3 3 3 3 4 3 " " 6 1 1 Shore A 79 73 77 77 78 78 80 TB (MPa) 7.5 5.1 6.9 8.69 6.9 6.9 8.41 TB (psi) 1090 740 1000 1260 1000 1000 1220 Comp. Set at 100 C 45 54 60 74 72 57 50 Melt Flow at 380 C 1.2 2.3 0.5 2.5 0.12 0.6 2.8 2160g (g/10 min) *Amorphous Elastomer 2 is 35% vinylidene fluoride, 34.2% hexafluoropropylene, 29% te trafluoroe thylene, 1.8% bromotetrafluorobutene 3 3 is 44% vinylidine fluoride, 28,86 HFP, 26% tetrafluoroethylene, 0.8t bromotetrafluorobutene, 0.4% fluorinated triallyl cyanurate 4 4 is 35% vinylidene fluoride, 36% hexafluoropropylene, 29% tetrafluoroethylene, 0.9% iodotetrafluorobutene **Thermoplastic 7 is 13% hexafluoropropylene, 87% tetrafluoroethylene n 8 is 77.6% tetrafluoroethylene, 19% ethylene, 3.4% perfluorobutyl ethylene II 9 is 97% tetrafluoroethylene, 3% perfluoropropyl vinyl ether ***Filler 1 is medium thermal carbon black " 2 is polytetrafluoroethylene powder ****Curing Agent 3 is meta phenylene bis maleimide " " 4 is triallyl isocyanurate " " 5 is 2,5 dimethyl-2,5 ditertbutyl peroxybenzene-3, 45% active ingredient on solid support n n 6 is cumene hydroperoxide Example 18 100 g of 19% solids latex of a copolymer of 258 tetrafluoroethylene, 45% vinylidene fluoriae, and 30% hexafluoropropylene was stirred while adding 3.5 g of a 50% solids aqueous suspension of zinc oxide and 1.5 g of hexamethylene diamine carbamate. After stirring for 1 hour, the liquid was transferreci to a Waring Blender and 40 g of a 19% solids suspension of thermoplastic 8 (Table II) in CC12F-CClF2 was added. The mixture was blended for 5 minutes resulting in a polymer suspension. This was filtered, and the clear filtrate was discarded. The rubbery solid was vacuum dried at 100 C. A slab was then melt pressea at 2900C. It was almost white in color and exhibited gooa strengtn and resilience. Snore A Hardness 88 Ult. Tensile 8.61 (mPa) 1250 psi Ult. Elongation 290% Melt Flow 7 g/10 mins at 3650C Example 19 Blending in Extruder The following rubber stock was prepared in a rubber mill at room temperature: Parts Copolymer of 25% Tetrafluoroethylene, 45% vinylidene fluoride, 308 hexafluoropropylene 70 MT Black 5 33% benzyl tripnenyl phosphonium chloride plus 67% copolymer of 608 vinylidene fluoride and 408 hexafluoropropylene 1.5 50% Bisphenol AF and 50% copolymer of 60% vinyllaine fluoride at 40% hexafluoropropylene 2.5 MgO 2.U The stock ss cut into 1/8" pellets an @ryblended with 30 parts of thermoplastic 8 Table II. This blend was ted into a 30 mm Werner & Pfleiaerer extruder, equipped with twin screws and kneading blocks, and extrusion-blended at 60 rpm, with a melt temperature of 295-3000C. The extruded strand was quenched and cut into pellets suitable for molding. Compression moldings of the product were tough and resilient. TB: 2100 psi Eb 320% Compression set: 3.5% after 22 hours at 1500C. Example 20 Extrusion Process Composition: 70/30 copolymer of vinylidene fluoride 60% and hexafluoropropylene 40% having a Mooney Viscosity of about 150/thermoplastic 6, Table II, 5 medium thermal carbon black, 1.0 part 33% benzyi triphenyl phosphonium chloride, plus 67% of a copolymer of 60% vinylidene fluoriae and 40% hexafluoropropylene, 1.25 50% Bisphenol AF plus 50% of a copolymer of 60% vinylidene fluoride and 40% hexafluoropropylene, 1.0 MgO. The curatives and the carbon black¯were milled into the vinylidene fluoride copolymer on cold mill. All the ingredients except the thermoplastic were ground 6 mm screen size and then dry blended with the thermoplastic before feeding to 28 mm Werne & Pfleiderer twin screw extruder, operating at 60 rpm. Feed Zone 2 Zone 3 Zones 4,5 Die 230-240 C 240-280 280-290 2850 280 The mixture melted at 295-3000C. The extrudate was quenched in water bath and pelletized. The product fed to 6 oz screw injection molding machine. Test plaques 3" x 5" x 1/16" molder with melt at 2900-3000C, mold at 60-900C. Cycle: 20 secs injection, 60 secs hold pressure 1200-1400 psi. Well-filled moldings were obtained. The moldings could be re-pelletized and fed back into the machine without loss of melt flow. Example 21 Seventy grams of perfluorinated elastomer having the composition 55.9% tetrafluoroethylene, 42.3% perfluoromethyl vinyl ether, 1.8% perfluoro phenoxy propyl vinyl ether was melted under a nitrogen blanket at 2800C and then 30 g of Teflon 1000 fluorinated ethylene propylene copolymer added. A uniform melt was obtained at 3200C and then coolea to 2500C with the mixer used in Example 1 operating at 90 rpm. To this were added 2.8 g 2,5,S,l5,18,21-hexaoxatricyclo [20.4.0.09,14]flexacosane; cyclo120.4.0.09,14]hexacosane. EMI13.1 and 2.8 9, Maglltes D MgO. The temperature was raised to 310 C during 15 minutes mastication after addition of MgO. The partly crumbled product was heated at 2450C for 16 hours in an air oven. The dark brown color of the product lightened while being heated in the air oven. The product compression molded at 3250C to give a slab from which samples were die cut. The properties were TB:16.55 MPa (2400 psi), EB:260%, Shore A hardness: 83, 150 C compression set:45% and melt flow:0.42 9/10 minutes at 3650C. Example 22 Sixty-three grams of the elastomer of Example 21 containing the following curatives and filler [all reported per hundred parts of elastomer] 4.0 parts 2,5,8,15,l8,21-hexaoxatricyclo [20.4.0.09.14]hexacosane, 3.0 parts EMI14.1 4.0 parts lead oxide, and 10.0 parts SAF carbon black, were added to 27 g Teflon 100 fluorinated ethylene. propylene copolymer in the mixer used in Example 1 at 3000C and mixed at 90 rpm for 15 minutes. The melt slowly crumbled as curing continued, The black product was eat treated in an air oven at 2450C for 16 hours. It compression molded easily at 3250C to form a slab which had the following properties: TB:16.55 MPa (2400 psi) EB:200%, Shore A hardness 67, 1500C compression set:24%, Melt flow:0.42 g/10 min. at 3650C, Example 23 Sixty-six parts by weight of Aflas 150P uncured fluoroelastomer derived from 41 mole percent propylene and 59 mole percent tetrafluoroethylene having an inherent viscosity of 1 as measured from a 0.1 wt % solution in tetrahydrofuran at 30 C, 34 parts by weight of Kynar@ 460 polyvinylidene fluoride resin having a melt flow of 3.4 g/10 mins measure at 2650C, and 13 parts by weight of MT Black carbon black were charged to a Brabender Plastograph and masticated at 1900C until a uniform blend was obtained. Two and three tenths parts by weight o sodium stearate, 5.7 parts by weight 1,3,5-triallyl-1,3,5-triazine- 2,4,6-(1H,3H,5H)-trione, and 2.8 parts by weight mand p- , '-bis(t-butylperoxy) diisopropyl benzene, 40% active ingredient on inert clay were addea to tne mixture and mastication continued at 1900C for 5 minutes. A sheet was compression molded at 2000C which sheet had the following propertiest Compression set 22 houra/1210C w 60, TB 1000 psi (6.9 MPa), EB = 45t, Perm. set " 4, Shore A Hardness = 86. The corresponding rubber ana carbon black blend masticated at 190 C, but not cured ha@ the following properties: Compression Set 22 hrs/1210C = 100, TB = 550 psi (3.8 MPa) EB = 140%, Perm. set = 25, Shore A hardness = 84. Example 24 Sixty-six parts by weight of the uncurea elastomer used in Example 23 and 34 parts by weight of a crystalline fluoroplastic having the composition 77.6% tetrafluoroethylene, 198 ethylene, 3.4% perfluorobutyl ethylene and 13 parts by weight MT Black carbon black were charged to a Brabender Plastograph and masticated at 280 C until a uniform blend was obtained. Two and three tenths parts sodium stearate, 4.0 parts, 2,5-dimethyl-3,5-di-tertbutyl peroxyhexane (45% active ingredient on solid support) and 4.5 parts by weight m-phenylene-bismaleimide were added to this mixture ana mastication continued at 2800C for 5 minutes. The proauct was postcured for 1 hour at 1800C in an air oven ano an additional hour at 2000C. A sheet was compression molded at 2900C which had the following properties: Compression Set 22 hours/1500C = 95; s/s, RT, 10"/min. M100 670; TB 680 psi (4.71 MPa); EB 1600; Perm. set = 66; Shore A hardness 78. The corresponding rubber and carbon black blend masticated at 2800C, but not cured, had the following properties: Compression set 22 hrs/1500 = 100; s/s, RT, 10" min. M100 = 380; TB = 170 psi (1.2 MPa); EB = 520%; perm. Set. 180; Shore A hardness = 78.

Claims: Claims; 1. A two-pnase composition having ci continuous pEs,se and a dispersed phase, the continuous phase consisting essentially of a melt-processable crystalline tnermoplastic fluorocarbon resin containing a minimum of 38 percent by weight fluorine, said dispersed phase consisting essentially of an amorphous crosslinked (vulcanizeo) fluoroelastomer containing a minimum ol 58 percent by weight fluorine, said dispersed phase constituting between about 50 and 90 percent by weight of the two phase composition. 2. ThD composition of Claim 1 in which the crystalline thermoplastic fluorocarbon resin is selected from the class consisting of fully fluorinated or partially fluorinated thermoplastic resins. 3. The composition of Claim 2 in whlch the amorphous crosslinked fluorocarbon elastomer is selected from the class consisting of fully fluorinated or partially fluorinateu fluoroelastomers. 4. A process for the preparation of the two-phase composition of Claim 1 which comprises (a) melt blending a melt-processable crystalline thermoplastic fluorocarbon resin containing a minimum of 38 percent by weight fluorine and an uncured fluoroelastomer containing a minimum of 58 percent by weight fluorine, (b) crosslinking the uncured fluoroelastomer while the crystalline thermoplastic fluorocarbon resin is at a temperature above its crystalline melting point and while the melt blend is undergoing mixing. 5. The process of Claim 4 in which a chemical curative is added to the melt blend at the beginning of the crosslinking step. 6. The process of Claim 4 in which the free radicals are generated during the crosslinking step. 7. The composition of Claim 1 in which the fluoroelastomer is vinylidene fluoride/hexafluoro- propylene/tetrafluoroethylene. 8. The composition of Claim 7 in whicn tne crystalline thermoplastic fluorocarbon resin is a tetrafluoroethylene/ethylene/perfluorobutyl ethylene.

Inventors: PAZOS, JOSE FRANCISCO, REES, RICHARD WATKIN
Applicants: E.I. DU PONT DE NEMOURS AND COMPANY
Application year: 1985
Main classification: C08L27
IPC codes: C08L27, C08J3