Fluorinated thermoplastic elastomers and articles therefrom

Abstract: Manufactured articles obtainable from a composition consisting of : 1) 100 phr of a fluorinated thermoplastic elastomer having a block structure with at least a fluorinated polymeric segment of B type having elastomeric properties and at least a fluorinated polymeric segment of A type having plastomeric properties, whereby the fluorinated thermoplastic elastomer comprises monomeric units which derive from an iodinated olefin, 2) from 0.1 to 40 phr of a crosslinking agent able to give peroxidic crosslinking of fluoroelastomers; and subsequent irradiation of the manufactured article by GAMMA or BETA radiations.

Description: The present invention relates to fluorinated thermoplastic elastomers having improved sealing properties, in particular at high temperatures, at least up to 150°C. As known, thermoplastic elastomers are block copolymers formed by at least a soft segment having elastomeric properties and by at least a hard segment having plastomeric properties. Such products combine therefore the properties typical of the conventional cured elastomers with those of the plastomers. In comparison with the conventional elastomers, they do not require any curing process, wherefore they result easily processable and recyclable according to the techniques usually utilized for thermoplastic polymers, with clear both economic and ecologic advantages. Fluorinated thermoplastic elastomers are known in the art. For instance in US patent 4,158,678, block fluorinated polymers, formed by alternate hard and soft segments, of which at least one is fluorinated, are described. Such products are obtained by radical polymerization of fluorinated monomers in the presence of an iodinated chain transfer agent having the formula RI n , wherein R is a fluorinated radical, optionally containing chlorine, having from 1 to 8 carbon atoms, and n is 1 or 2, thus obtaining a first fluorinated polymeric segment, with elastomeric or plastomeric characteristics depending on the monomeric composition, having an iodine atom on one or both end groups. On such segment other different fluorinated or non fluorinated segments are then grafted, considering that the terminal iodine atoms are susceptible of radical attack and can therefore produce the growth of a new polymeric chain. It is thus possible to obtain, for instance, fluorinated thermoplastic elastomers of the A-B-A type, wherein A is a plastomeric segment (for instance a homopolymer or copolymer deriving from tetrafluoroethylene and/or vinylidenefluoride), while B is an elastomeric segment (for instance a tetrafluoroethylene/vinylidene fluoride/hexafluoropropene copolymer. Other thermoplastic elastomers of this kind are described in EP 444,700. A limit of such products consists in that the mechanical and elastic properties easily worsen when the temperature rises and result quite unsatisfactory already at 50°C. In particular the compression set values are high, such as to make the products unsuitable to the manufacture of sealing elements (for instance shaft seals or O-rings or the like) to be employed at high temperatures, as requested by the motor, aerospace, plant industry. Fluorinated thermoplastic elastomers, having improved mechanical and elastic properties by the introduction in the polymeric chain of small amounts of a bis-olefin, are also known from USP 5,612,419. The resulting products are in particular characterized by improved mechanical properties and by particularly low compression set values in comparison with the fluorinated thermoplastic elastomers of the patents previously described. New fluorinated thermoplastic elastomers are also known from EP patent 683,186, which have mechanical and elastomeric properties similar to the products of US patent 5,612,419 but having in the chain instead of the bis-olefin, small amounts of a fluorinated olefin containing a terminal iodine atom. However the sealing properties of the products mentioned above are not satisfactory at high temperatures, in particular at the temperature of 150°C. WO-A-9102770 provides a polymer blend of a fluoroplastic and a fluoroelastomer, optioanally crosslinkable, which combine thermoprocessability and chemical inertness of a thermoplastic with rubbery properties of an elastomer. The need was felt to have available thermoplastic elastomers with improved sealing properties at high temperatures, in particular the compression set (C set). An object of the present invention are manufactured articles obtainable from a composition consisting essentially of: 1) 100 phr of a fluorinated thermoplastic elastomer having a block structure with at least a fluorinated polymeric segment of type B having elastomeric properties and at least a fluorinated polymeric segment of type A having plastomeric properties, 2) from 0.1 to 40 phr of a crosslinking agent able to give peroxidic crosslinking of fluoroelastomers; and subsequent radiation of the manufactured article by GAMMA radiations, from 1 to 50 Mrad, preferably from 1 to 30 Mrad, or BETA radiations from 10 to 500 KGy, preferably from 10 to 300 KGy. Preferably the amount of the component 2) ranges from 1 to 10 phr. The composition of the invention can contain other additives such as fillers, for instance carbon black, silica, stabilizers, antioxidants, pigments, thickeners, plastifiers, etc. The amount of these additives generally ranges from 0.5 to 40 phr, preferably from 1 to 20 phr. The crosslinking agents which can be used are for instance: triallyl-cyanurate; triallyl-isocyanurate (TAIC); tris(diallylamine)-s-triazine; triallylphosphite; N,N-diallyl-acrylamide; fluorinated bis-olefins as defined hereinafter, N,N' bisallylbicycle-oct-7-ene-disuccinimide (BOSA); N,N,N'-tetraallyl-malonamide; trivinyl-isocyanurate; 2,4,6-trivinyl-methyltrisiloxane, etc. A crosslinking agent or a mixture of the crossliniking agents above mentioned can be utilized. It has been found that the compositions of the invention subjected to treatment with BETA or GAMMA radiations give a remarkable increase of the sealing properties, even at high temperatures up to 150°C. The effect is particularly meaningful when the thermoplastic elastomer contains as plastomeric block the one essentially formed by PVDF. In this case, it is sufficient a very low amount of radiations, for instance 1 Mrad of GAMMA rays, to obtain the improved sealing properties. As preferred crosslinking agents, TAIC, 1,6 divinylperfluorohexane (bis-olefin), BOSA can be mentioned, which have the following structures: The fluorinated thermoplastic elastomer consists essentially of a block structure with at least a fluorinated polymeric segment of B type having elastomeric properties and at least a fluorinated polymeric segment of A type having plastomeric properties, with at least one of the segments of A or B type, preferably B, wherein monomeric units are present deriving from at least an iodinated olefin having the formula: CX 2 =CX-R f -CHR-I wherein: X is -H, -F, or -CH 3 ; R is -H or -CH 3 ; R f is a (per)fluoro-alkylenic, linear or branched radical, optionally containing one or more atoms of ether oxygen, or a (per)fluoropoly-oxyalkylenic radical. Iodinated olefins according to the formula (I B) can be selected in particular from the following classes: (1) CHR=CH-Z-CH 2 CHR-I wherein: R is -H or -CH 3 ; Z is a (per)fluoroalkylenic radical C 1 -C 18 , linear or branched, optionally containing one or more atoms of ether oxygen, or a (per)fluoropolyoxyalkylenic radical; (2) CF 2 =CF-O-(CF 2 CFYO) n -(CF 2 CF 2 CH 2 O) m -CF 2 CF 2 CH 2 I wherein: Y is -F or -CF 3 ; m is an integer in the range 0-5; n is 0, 1 or 2. As for the formula (II B), Z is preferably a perfluoroalkylenic radical C 4 -C 12 , or a (per)fluoropolyoxyalkylenic radical, as defined in formula (II A). The unit amount deriving from the iodinated olefins of formula (I B) is generally in the range 0.01-1.0 by mole, preferably 0.03-0.5 by mole, still more preferably 0.05-0.2 by mole per 100 moles of the other basic monomeric units of the elastomer or of the plastomer. The olefins of formula (I B) are described in EP 683,186 incorporated herein by reference. The fluorinated elastomer and the fluorinated plastomer are obtained by (co)polymerization of olefinic monomers. With fluorinated olefinic monomers are meant all the fluorinated products having at least a double bond C=C, optionally containing hydrogen and/or chlorine and/or bromine and/or iodine and/or oxygen, capable of producing (co)polymers in the presence of radical initiators. Among them we can cite: perfluoroolefins C 2 -C 8 , such as tetrafluoroethylene (TFE), hexafluoropropene (HFP), hexafluoroisobutene; hydrogenated fluoroolefins C 2 -C 8 , such as vinyl fluoride (VF), vinilydene fluoride (VDF), trifluoroethylene, perfluoroalkylethylene CH 2 =CH-R f , wherein R f is a perfluoroalkyl C 1 -C 6 ; chloro- and/or bromo- and/or iodo-fluoroolefins C 2 -C 8 , such as chlorotrifluoroethylene (CTFE) and bromotrifluoroethylene; (per)fluoroalkylvinylethers (PAVE) CF 2 =CFOR f , wherein R f is a (per)fluoroalkyl C 1 -C 6 , for instance trifluoromethyl, bromodifluoromethyl or pentafluoropropyl; (per)fluoro-oxyalkylvinylethers CF 2 =CF-OX, wherein X is a (per)fluoro-oxyalkyl C 1 -C 12 having one or more ether groups, for instance perfluoro-2-propoxy-propyl; perfluorodioxoles. Such fluorinated olefinic monomers can also be copolymerized with non fluorinated olefins C 2 -C 8 , such as ethylene, propylene, isobutylene. The type B segments (elastomeric) can in particular be selected from the following classes (compositions expressed as % by mole): (1) VDF-based copolymers, wherein VDF is copolymerized with at least a comonomer selected from: perfluoroolefins C 2 -C 8 ; chloro- and/or bromo- and/or iodo-fluoroolefins C 2 -C 8 ; (per)fluoroalkylvinylethers (PAVE) or (per)fluoro-oxyalkylvinylethers above defined; non fluorinated olefins (Ol) C 2 -C 8 ; typical compositions are the following: (a) VDF 45-85%, HFP 15-45%, TFE 0-30%; (b) VDF 50-80%, PAVE 5-50%, TFE 0-20%; (c) VDF 20-30%, Ol 10-30%, HFP and/or PAVE 18-27%, TFE 10-30%; (2) TFE-based copolymers, wherein TFE is copolymerized with at least a comonomer selected from: (per)fluoroalkylvinylethers (PAVE) or (per)fluorooxyalkylvinylethers above defined; hydrogenated fluoroolefins C 2 -C 8 ; fluoroolefins C 2 -C 8 containing clorine and/or bromine and/or iodine atoms; non fluorinated olefins (Ol) C 2 -C 8 ; typical compositions are the following: (a) TFE 50-80%, PAVE 20-50%; (b) TFE 45-65%, Ol 20-55%, VDF 0-30%; (c) TFE 32-60%, Ol 10-40%, PAVE 20-40%. The type A segments (plastomeric) can in particular be selected from the following classes (compositions expressed as % by mole): (1) polytetrafluoroethylene or modified polytetrafluoroethylene containing small amounts, generally in the range 0.1-3%, preferably lower than 0.5%, of one or more comonomers such as, for instance: HFP, PAVE, VDF, hexafluoroisobutene, CTFE, perfluorolalkylethylenes; (2) TFE thermoplastic polymers containing from 0.5 to 8% of at least a PAVE, such as, for instance, TFE and perfluoropropylvinylether and/or perfluoromethylvinylether copolymers, or also TFE/perfluoroalkylethylene copolymers; (3) TFE thermoplastic polymers containing from 2 to 20% of a perfluoroolefin C 3 -C 8 , such as, for instance, FEP (TFE/HFP copolymer), to which other comonomers having a vinylether structure CF 2 =CF-OR f or CF 2 =CF-OX defined as above can be added in small amounts (lower than 5%); (4) TFE or CTFE copolymers (40-60%) with ethylene, propylene or isobutylene (40-60%), optionally containing as third comonomer a (per)fluoroolefin C 3 -C 8 or a PAVE, in amounts in the range 0.1-10%; (5) polyvinylidenfluoride or modified polyvinylidenfluoride containing small amounts, generally comprised between 0.1 and 10%, of one or more fluorinated comonomers, such as hexafluoropropene, tetrafluoroethylene, trifluoroethylene. The thermoplastic polymers of the classes above indicated, and in particular the TFE-based polymers, can be modified with (per)fluorinated dioxoles, according to the patents US-3,865,845, US-3,978,030, EP-73,087, EP-76,581, EP-80,187. It has been found by Applicants that the mechanical and sealing properties of the manufactured articles, after GAMMA or BETA irradiation, can be further improved by subjecting the articles so obtained to a thermal treatment for about 1-6 hours at a temperature lower of about 10°-30°C with respect to the melting temperature of the plastomer. This treatment can be called annealing. Applicants have also found that the above properties are further incresed if the above thermal treatment is carried on the manufactured articles before subjecting them to GAMMA or BETA irradiation.

Claims: Manufactured articles obtainable from a composition consisting of: 1) 100 phr of a fluorinated thermoplastic elastomer having a block structure with at least a fluorinated polymeric segment of B type having elastomeric properties and at least a fluorinated polymeric segment of A type having plastomeric properties, whereby in at least one among the A or B type segments monomeric units are present which derive from at least an iodinated olefin having the formula: CX 2 =CX-R f -CHR-I wherein: X is -H, -F, or -CH 3 ; R is -H or -CH 3 ; R f is a (per)fluoroalkylenic, linear or branched radical, optionally containing one or more atoms of ether oxygen, or a (per)-fluoropolyoxyalkylenic radical; 2) from 0.1 to 40 phr of a crosslinking agent able to give peroxidic crosslinking of fluoro-elastomers; and subsequent radiation of the manufactured article by GAMMA radiations, from 1 to 50 Mrad, or BETA radiations from 10 to 500 KGy. Manufactured articles according to claim 1 wherein the component 2) amount ranges from 1 to 10 phr. Manufactured articles according to claims 1 and 2 wherein the composition contains additives such as fillers, stabilizers, antioxidants, pigments, thickeners and plastifiers. Manufactured articles according to claims 1-3 wherein the crosslinking agents are selected from 1,6-divinylperfluorohexane; triallyl-cyanurate; triallyl-isocyanurate (TAIC); tris(diallylamine)-s-triazine; triallylphosphite; N,N-diallyl-acrylamide; fluorinated bis-olefins, N,N'-bisallylbicycle-oct-7-ene-disuccinimide (BOSA); N,N,N',N'-tetraallyl-malonamide; trivinyl-isocyanurate; and 2,4,6-trivinyl-methyltrisiloxane. Manufactured articles according to claim 4, wherein the crosslinking agents are selected from TAIC, 1,6 divinylperfluorohexane, and BOSA. Manufactured articles according to claim 5, wherein the iodinated olefin is present in the fluorinated polymeric segment of type B having elastomeric properties. Manufactured articles according to claim 6, wherein the iodinated olefin is selected from the following classes: (1) CHR=CH-Z-CH 2 CHR-I wherein: R is -H or -CH 3 ; Z is a (per)fluoroalkylenic radical C 1 -C 18 , linear or branched, optionally containing one or more atoms of ether oxygen, or a (per)fluoropolyoxyalkylenic radical; (2) CF 2 =CF-O-(CF 2 CFYO) n -(CF 2 CF 2 CH 2 O) m -CF 2 CF 2 CH 2 I wherein: Y is -F or -CF 3 ; -m is an integer in the range 0-5; n is 0, 1 or 2. Manufactured articles according to claim 7 wherein the amount of units deriving from the iodinated olefin is in the range 0.01-1.0 by mole per 100 moles of the other monomeric units of the elastomer or the plastomer. Manufactured articles according to claim 8 wherein the fluorinated elastomer and the fluorinated plastomer blocks are obtained by (co)polymerization of fluorinated olefinic monomers having at least a double bond C=C, optionally containing hydrogen and/or chlorine and/or bromine and/or iodine and/or oxygen, able to produce (co)-polymers in the presence of radical initiators. Manufactured articles according to claim 9 wherein the fluorinated olefinic monomers are selected from: perfluoroolefins C 2 -C 8 , such as tetrafluoroethylene (TFE), hexafluoropropene (HFP), and hexafluoroisobutene; hydrogenated fluoroolefins C 2 -C 8 , such as vinyl fluoride (VF), vinylidene fluoride (VDF), trifluoroethylene, and perfluoroalkylethylene CH 2 =CH-R f , wherein R f is a perfluoroalkyl C 1 -C 6 ; chloro- and/or bromo- and/or iodo-fluoroolefins C 2 -C 8 , such as chlorotrifluoroethylene (CTFE) and bromotrifluoroethylene; (per)fluoroalkylvinylethers (PAVE) CF 2 =CFOR f , wherein R f is a (per)-fluoroalkyl C 1 -C 6 , such as trifluoromethyl, bromodifluoromethyl or pentafluoropropyl; (per)fluorooxyalkylvinylethers CF 2 =CFOX, wherein X is a (per)fluorooxyalkyl C 1 -C 12 having one or more ether groups, such as perfluoro-2-propoxy-propyl; and perfluorodioxoles. Manufactured articles according to claim 10 wherein the fluorinated olefinic monomers are copolymerized in the presence of non fluorinated olefins C 2 -C 8 , such as ethylene, propylene, isobutylene. Manufactured articles according to claim 11 wherein the B type segments (elastomeric) are selected from the following classes: (1) VDF-based copolymers, wherein VDF is copolymerized with at least a comonomer selected from: perfluoroolefine C 2 -C 8 ; chloro- and/or bromo- and/or iodo-fluoroolefins C 2 -C 8 ; (per)fluoroalkylvinylethers (PAVE) or (per)fluorooxyalkylvinylethers above defined; non fluorinated olefins (Ol) C 2 -C 8 ; and (2) TFE-based copolymers, wherein TFE is copolymerized with at least a comonomer selected from: (per)fluoroalkylvinylethers (PAVE) or (per)fluorooxyalkylvinylethers above defined; hydrogenated fluoroolefins C 2 -C 8 ; fluoroolefins C 2 -C 8 containing clorine and/or bromine and/or iodine atoms; non fluorinated olefins (Ol) C 2 -C 8 ; Manufactured articles according to claim 12 wherein the type A segments (plastomeric) are selected from the following classes: (1) polytetrafluoroethylene or modified polytetrafluoroethylene with amounts in the range 0.1-3%, preferably lower than 0.5%, of one or more comonomers such as HFP, PAVE, VDF, hexafluoroisobutene, CTFE, perfluoroalkylethylenes; (2) TFE thermoplastic polymers containing from 0.5 to 8% of at least a PAVE, such as TFE/perfluoropropylvinylether copolymers and/or TFE/perfluoromethylvinylether copolymers, or also TFE/perfluoroalkylethylene copolymers; (3) TFE thermoplastic polymers containing from 2 to 20% of a perfluoroolefin C 3 -C 8 , such as FEP (TFE/HFP copolymer), to which amounts lower than 5% of other comonomers having a vinylether structure CF 2 =CF-OR f or CF 2 =CF-OX above defined can be added; (4) TFE or CTFE copolymers (40-60%) with ethylene, propylene or isobutylene (40-60%), optionally containing as third comonomer a (per)fluoroolefin C 3 -C 8 or a PAVE, in amounts in the range 0.1-10%; (5) polyvinylidenfluoride or modified polyvinylidenfluoride with amounts in the range 0.1-10%, of one or more fluorinated comonomers, such as hexafluoropropene, tetrafluoroethylene, trifluoroethylene. Manufactured articles according to claim 13 wherein the thermoplastic polymers are modified with (per) fluorinated dioxoles. Manufactured articles according to claim 14 wherein the manufactured articles before being subjected to irradiation treatment are subjected to a thermal treatment for 1-6 hours at a temperature 10°-30°C lower than the melting point of plastomer A. Manufactured articles according to claim 15 wherein the manufactured articles after being subjected to irradiation treatment are subjected to a thermal treatment for 1-6 hours at a temperature 10°-30°C lower than the melting point of plastomer A. Manufactured aricles according to claim 12 wherein the VDF-based copolymers are selected from (compositions expressed as % by moles): (a) VDF 45-85%, HFP 15-45%, 0-30% TFE; (b) VDF 50-80%, PAVE 5-50%, TFE 0-20%; (c) VDF 20-30%, Ol 10-30%, HFP and/or PAVE 18-27%, TFE 10-30%; and the TFE-based copolymers are selected from (compositions expressed as % by moles): (a) TFE 50-80%, PAVE 20-50%; (b) TFE 45-65%, Ol 20-55%, 0-30% VDF; (c) TFE 32-60%, Ol 10-40%, PAVE 20-40%. Use of a composition consisting of: 1) 100 phr of a fluorinated thermoplastic elastomer having a block structure with at least a fluorinated polymeric segment of B type having elastomeric properties and at least a fluorinated polymeric segment of A type having plastomeric properties, whereby in at least one among the A or B type segments monomeric units are present which derive from at least an iodinated olefin having the formula: CX 2 =CX-R f -CHR-I wherein: X is -H, -F, or -CH 3 ; R is -H or -CH 3 ; R f is a (per)fluoroalkylenic, linear or branched radical, optionally containing one or more atoms of ether oxygen, or a (per)-fluoropolyoxyalkylenic radical; 2) from 0.1 to 40 phr of a crosslinking agent able to give peroxidic crosslinking of fluoro-elastomers; for the preparation of manufactured articles having improved sealing properties at high temperatures, by irradiating the composition with GAMMA radiations, from 1 to 50 Mrad, or BETA radiations from 10 to 500 KGy. Use according to claim 18 wherein the component 2) amount ranges from 1 to 10 phr. Use according to claim 18 wherein the composition contains additives such as fillers, stabilizers, antioxidants, pigments, thickeners and plastifiers. Use according to claim 18 wherein the crosslinking agents are selected from 1,6-divinylperfluorohexane; triallyl-cyanurate; triallyl-isocyanurate (TAIC); tris(diallylamine)-s-triazine; triallylphosphite; N,N-diallyl-acrylamide; fluorinated bis-olefins, N,N'-bisallylbicycle-oct-7-ene-disuccinimide (BOSA); N,N,N'N'-tetraallyl-malonamide; trivinyl-isocyanurate; and 2,4,6-trivinyl-methyltrisiloxane. Use according to claim 21, wherein the crosslinking agents are selected from TAIC, 1,6 divinylperfluorohexane and BOSA.

Inventors: ALBANO MARGHERITA, ARCELLA VINCENZO, GAYER UDO, SCHUH THOMAS, ALBANO, MARGHERITA, ARCELLA, VINCENZO, GAYER, UDO, SCHUH, THOMAS
Applicants: SOLVAY SOLEXIS SPA, SOLVAY SOLEXIS S.P.A.
Application year: 1998
Main classification: C08L27
IPC codes: C08F287, C08K5, C08F293