Patent Application
20160177079
The present invention relates to a fluorine-containing thermoplastic elastomer composition, comprising a continuous thermoplastic fluorocarbon polymer phase and a dispersed vulcanized fluorine-containing elastomer phase, which is useful as melt-formable material having rubber elasticity.
Two-phase compositions comprising a continuous phase thermoplastic material and a disperse phase elastomer, produced by dynamically vulcanizing the elastomer while the dispersed phase elastomer is mixed under shear in the continuous thermoplastic material kept in the molten state are well known in the art and often referred to as thermoplastic vulcanizates (TPV).
These materials are particularly advantageous in that they derive their rubber-like properties from the dispersed phase, so that they can be notably used in all rubber-typical fields of use (sealing articles, including seals and gaskets, pipes, hoses, flat sheets, and the like), While being processable as thermoplasts, including possibility of reforming scraps, flashes or defective parts.
Because of advantageous properties of fluorine-containing materials, TPV including both thermoplastic fluorinated polymer continuous phase, and more specifically an ethylene-chlorotrifluoroethylene or ethylene-tetrafluoroethylene phase, and fluorine-containing elastomer dispersed phase have attracted great deal of attention for providing outstanding thermal resistance, chemical resistance, and the like.
For instance, patent document EP 168020 A (DUPONT DE NEMOURS) 15 Jan. 1986 discloses fluorinated thermoplastic elastomer containing two phases, namely a crystalline thermoplastic phase and a dispersed fluorinated amorphous elastomeric phase, obtained by blending the components in the molten state and then dynamically curing the same, e.g. in an extruder through addition of a curing agent (ionic curing or peroxide curing). Thermoplastic polymer can be notably ECTFE; example 9 pertains to the preparation in a Braebender of a TPV comprising 70% wt vinylidene fluoride (VDF)/hexafluoropropylene (HFP) copolymer and 30% wt of ECTFE copolymer (CTFE/E 80/20 wt/wt) by ionic curing.
Still, patent document U.S. Pat. No. 5,006,594 (DUPONT DE NEMOURS) 9 Apr. 1991 discloses new blends of fluorinated thermoplastic elastomers containing a two-phase composition including a continuous phase of a melt processable resin and a dispersed phase of an amorphous crosslinked fluoroelastomer. ETFE and ECTFE are mentioned as possible thermoplastic fluororesin.
It is nevertheless well known that for a TPV material to deliver its performances, it is essential to ensure adequate crosslinking of the dispersed elastomer phase during dynamic vulcanization. Several technologies have been developed for optimizing dynamic vulcanization of the elastomer phase.
Thus, patent document U.S. Pat. No. 5,354,811 (ASAHI GLASS COMPANY LTD) 11 Oct. 1994 is directed to certain fluorine-containing thermoplastic elastomer compositions comprising a continuous phase of at least one melt-formable thermoplastic fluorocarbon resin and a disperse phase of vulcanizate of fluorine-containing elastomer. The thermoplast can be notably ECTFE or ETFE. For improving vulcanization efficiency, the fluorine-containing elastomer has specific vulcanizable sites, selected from the group consisting of epoxy groups, carboxylic groups, sulfonic groups, and derivatives thereof.
Increasing amounts of curative is another solution, which might lead to additional drawbacks, including e.g. the need of eliminating unreacted curatives. Patent document US 2005/0281973 (FREUDENBERG-NOK) 22 Dec. 2005 is directed to a method for manufacturing processable rubber compositions containing dynamic vulcanizates of fluorocarbon elastomer in a continuous phase of a thermoplastic material, including a step of heat treatment for decomposing and driving off un-reacted polyol curatives, before further processing of the TPV by thermoplastic techniques to form shaped articles. As thermoplast, ECTFE and ETFE can be used.
There is thus a continuous need in the art for TPV compositions wherein the elastomer dispersed phase is effectively cured, with high crosslinking kinetics and good efficiency, so as to deliver rubber properties in the final compound.
The Applicant has now found that the incorporation in the TPV composition of certain polymer having ionisable groups is particularly effective in ensuring optimized dynamic crosslinking of the elastomer phase.
It is thus hereby provided a thermoplastic vulcanizate fluorine-containing composition [vulcanizate (C)], comprising a continuous thermoplastic fluoropolymer phase and a dispersed vulcanized fluoroelastomer phase, said composition comprising:
The Applicant has surprisingly found that the incorporation in the vulcanizate (C), as above detailed, of the ionomer (I) is particularly beneficial for improving kinetics of dynamic vulcanization of the fluoroelastomer within the thermoplastic fluoropolymer matrix, so as to ensure optimum rubber-like performances of the resulting TPV compound.
The invention further pertains to a precursor mixture [mixture (M)] of a thermoplastic vulcanizate fluorine-containing composition, said composition comprising:
The invention further pertains to a method for manufacturing the vulcanizate (C), as above detailed, comprising dynamic curing of the precursor mixture, as above detailed.
Polymer (F) is a thermoplast, that is to say a polymer which softens on heating and hardens on cooling at room temperature, which at room temperature exists below its glass transition temperature if amorphous or below its melting point if semi-crystalline.
It is nevertheless generally preferred for the polymer (F) to be semi-crystalline, that is to say to have a definite melting point; preferred polymers (F) are those possessing a heat of fusion of at least 5 J/g, preferably of at least 10 J/g, more preferably at least 30 J/g. Without upper limit for heat of fusion being critical, it is nevertheless understood that polymer (A) will generally possess a heat of fusion of at most 55 J/g, preferably of at most 53 J/g, more preferably of at most 50 J/g.
Heat of fusion is generally determined by DSC according to ASTM D1638 standard.
Polymer (F) is fluorinated, that is to say it comprises recurring units derived from at least one fluorinated monomer [monomer (F)].
The monomer (F) is generally selected from the group consisting of:
(a) C2-C8 perfluoroolefins, such as tetrafluoroethylene, and hexafluoropropene;
(b) C2-C8 hydrogenated fluoroolefins, such as vinyl fluoride, 1,2-difluoroethylene, vinylidene fluoride and trifluoroethylene;
(c) perfluoroalkylethylenes complying with formula CH2═CH—Rf0, in which Rf0 is a C1-C6 perfluoroalkyl;
(d) chloro- and/or bromo- and/or iodo-C2-C6 fluoroolefins, like chlorotrifluoroethylene;
(e) (per)fluoroalkylvinylethers complying with formula CF2═CFORf1 in which Rf1 is a C1-C6 fluoro- or perfluoroalkyl, e.g. CF3, C2F5, C3F7;
(f) CF2═CFOX0 (per)fluoro-oxyalkylvinylethers, in which X0 is a C1-C12 alkyl, or a C1-C12 oxyalkyl, or a C1-C12 (per)fluorooxyalkyl having one or more ether groups, like perfluoro-2-propoxy-propyl;
(g) (per)fluoroalkylvinylethers complying with formula CF2═CFOCF2ORf2 in which Rf2 is a C1-C6 fluoro- or perfluoroalkyl, e.g. CF3, C2F5, C3F7 or a C1-C6 (per)fluorooxyalkyl having one or more ether groups, like —C2F5—O—CF3;
(h) functional (per)fluoro-oxyalkylvinylethers complying with formula CF2═CFOY0, in which Y0 is a C1-C12 alkyl or (per)fluoroalkyl, or a C1-C12 oxyalkyl, or a C1-C12 (per)fluorooxyalkyl having one or more ether groups and Y0 comprising a carboxylic or sulfonic acid group, in its acid, acid halide or salt form;
(i) fluorodioxoles, of formula (I):
wherein each of Rf3, Rf4, Rf5, Rf6, equal or different each other, is independently a fluorine atom, a C1-C6 fluoro- or per(halo)fluoroalkyl, optionally comprising one or more oxygen atom, e.g. —CF3, —C2F5, —C3F7, —OCF3, —OCF2CF2OCF3.
The polymer (F) might comprise recurring units derived from one or from more than one monomers (F), as above detailed. Further, in addition, polymer (F) may comprise recurring units derived from one or more fluorine-free monomers.
Polymer (F) used in the TPV composition of this invention typically comprises:
(j) from 40 to 60% by moles of recurring units derived from ethylene (E);
(jj) from 60 to 40% by moles of recurring units derived from at least one of chlorotrifluoroethylene (CTFE) and tetrafluoroethylene (TFE); and
(jjj) from 0 to 10% by moles, preferably from 0 to 5%, more preferably from 0 to 2.5% by moles, of recurring units derived from of at least one fluorinated and/or fluorine-free comonomer(s) different from E, CTFE and TFE.
The comonomer (jjj) can be a fluorine-free comonomer selected from the group consisting of:
1) acrylic monomers having general formula: CH2═CH—CO—O—R2 wherein R2 is a C1-C20 hydrocarbon group, optionally containing one or more heteroatoms;
2) vinylether monomers having general formula: CH2═CH—O—R2 wherein R2 is a C1-C20 hydrocarbon group, optionally containing one or more heteroatoms;
3) vinyl esters of the carboxylic acid having general formula: CH2═CH—O—CO—R2 wherein R2 is a C1-C20 hydrocarbon group, optionally containing one or more heteroatoms;
4) unsaturated carboxylic acids having general formula CH2═CH—(CH2)n—COOH wherein n is 0 or an integer of 1 to 10.
The comonomer (jjj) can be a fluorinated comonomer; in such case, comonomer (jjj), provided is different from monomer (jj) (i.e. from CTFE or from TFE) can be any of monomers listed above under (a) to (i), and more particularly can be a monomer of type (e), as above detailed.
Among polymers (F), ECTFE copolymers, i.e. copolymers wherein monomer (jj) is CTFE, i.e. in other words, copolymers of ethylene and CTFE (and optionally a third monomer, as above detailed) are preferred.
ECTFE polymers suitable in the composition of the invention typically possess a melting temperature exceeding 220° C., preferably exceeding 225° C., even exceeding 230° C., preferably exceeding 235° C. The melting temperature is determined by Differential Scanning calorimetry (DSC) at a heating rate of 10° C./min, according to ASTM D 3418.
ECTFE polymers which have been found to give particularly good results in the composition of the invention are those consisting essentially of recurring units derived from:
(j) from 46 to 52% by moles of ethylene (E);
(jj) from 54 to 48% by moles of chlorotrifluoroethylene (CTFE), based on the sum of (j) and (jj), and, optionally
(jjj) from 0.01 to 5% by moles, based on the sum of (j), (jj) and (jjj), of at least one (per)fluoroalkylvinylethers complying with formula CF2═CFORf1 in which Rf1 is a C1-C6 fluoro- or perfluoroalkyl, e.g. CF3, C2F5, C3F7.
End chains, defects or minor amounts of monomer impurities leading to recurring units different from those above mentioned can be still comprised in the preferred ECTFE, without these affecting properties of the material.
The melt flow rate of the ECTFE polymer, measured following the procedure of ASTM 3275-81 at 230° C. and 2.16 Kg, ranges generally from 0.01 to 75 g/10 min, preferably from 0.1 to 50 g/10 min, more preferably from 0.5 to 30 g/10 min.
For the purposes of this invention, the term “(per)fluoroelastomer” [elastomer (A)] is intended to designate a fluoropolymer resin serving as a base constituent for obtaining a true elastomer, said fluoropolymer resin comprising more than 10% wt, preferably more than 30% wt, of recurring units derived from at least one ethylenically unsaturated monomer comprising at least one fluorine atom (hereafter, (per)fluorinated monomer) and, optionally, recurring units derived from at least one ethylenically unsaturated monomer free from fluorine atom (hereafter, hydrogenated monomer).
True elastomers are defined by the ASTM, Special Technical Bulletin, No. 184 standard as materials capable of being stretched, at room temperature, to twice their intrinsic length and which, once they have been released after holding them under tension for 5 minutes, return to within 10% of their initial length in the same time.
Non limitative examples of suitable (per)fluorinated monomers are notably: —C2-C8 fluoro- and/or perfluoroolefins, such as tetrafluoroethylene (TFE), hexafluoropropene (HFP), pentafluoropropylene, and hexafluoroisobutylene;
wherein each of Rf3, Rf4, Rf5, Rf6, equal or different each other, is independently a fluorine atom, a C1-C6 fluoro- or per(halo)fluoroalkyl, optionally comprising one or more oxygen atom, e.g. —CF3, —C2F5, —C3F7, —OCF3, —OCF2OF2OCF3.
Examples of hydrogenated monomers are notably hydrogenated alpha-olefins, including ethylene, propylene, 1-butene, diene monomers, styrene monomers, alpha-olefins being typically used.
(Per)fluoroelastomers (A) are in general amorphous products or products having a low degree of crystallinity (crystalline phase less than 20% by volume) and a glass transition temperature (Tg) below room temperature. In most cases, the (per)fluoroelastomer has advantageously a Tg below 10° C., preferably below 5° C., more preferably 0° C.
The (per)fluoroelastomer (A) is preferably selected among:
(1) VDF-based copolymers, in which VDF is copolymerized with at least one comonomer selected from the group consisting of the followings classes, with the provision that such comonomer is different from VDF:
(a1) C2-C8 perfluoroolefins, such as tetrafluoroethylene (TFE), hexafluoropropylene (HFP), hexafluoroisobutylene;
(b1) hydrogen-containing C2-C8 olefins, such as C2-C8 non-fluorinated olefins (Ol); C2-C8 partially fluorinated olefins, vinyl fluoride (VF), trifluoroethylene (TrFE), perfluoroalkyl ethylenes of formula CH2═CH—Rf, wherein Rf is a C1-C6 perfluoroalkyl group;
(c1) C2-C8 chloro and/or bromo and/or iodo-fluoroolefins such as chlorotrifluoroethylene (CTFE);
(d1) (per)fluoroalkylvinylethers of formula CF2═CFORf, wherein Rf is a C1-C6 (per)fluoroalkyl group; preferably perfluoroalkylvinylethers (PAVE) of above formula wherein Rf is C1-C6 perfluoroalkyl group, e.g. CF3, C2F5, C3F7;
(e1) (per)fluoro-oxy-alkylvinylethers of formula CF2═CFOX, wherein X is a C1-C12 ((per)fluoro)-oxyalkyl comprising catenary oxygen atoms, e.g. the perfluoro-2-propoxypropyl group;
(f1) (per)fluorodioxoles having formula:
wherein Rf3, Rf4, Rf5, Rf6, equal or different from each other, are independently selected among fluorine atoms and C1-C6 (per)fluoroalkyl groups, optionally comprising one or more than one oxygen atom, such as notably —CF3, —C2F5, —C3F7, —OCF3, —OCF2CF2OCF3; preferably, perfluorodioxoles;
(g1) (per)fluoro-methoxy-vinylethers (MOVE, hereinafter) having formula: CFX2═CX2OCF2OR″f
wherein R″f is selected among C1-C6 (per)fluoroalkyls, linear or branched; C5-C6 cyclic (per)fluoroalkyls; and C2-C6 (per)fluorooxyalkyls, linear or branched, comprising from 1 to 3 catenary oxygen atoms, and X2═F, H; preferably X2 is F and R″f is —CF2CF3 (MOVE1); —CF2CF2OCF3 (MOVE2); or —CF3 (MOVE3);
(h1) C2-C8 non-fluorinated olefins (Ol), for example ethylene and propylene; and
(2) TFE-based copolymers, in which TFE is copolymerized with at least one comonomer selected from the group consisting of the classes (a1),
(c1), (d1), (e1), (g1), (h1), and class (i2) below, with the provision that such comonomer is different from TFE:
(i2) perfluorovinyl ethers containing cyanide groups, such as notably those described in patents U.S. Pat. No. 4,281,092, U.S. Pat. No. 5,447,993 and U.S. Pat. No. 5,789,489.
Most preferred (per)fluoroelastomers (A) are those having following compositions (in mol %):
(i) vinylidene fluoride (VDF) 35-85%, hexafluoropropene (HFP) 10-45%, tetrafluoroethylene (TFE) 0-30%, perfluoroalkyl vinyl ethers (PAVE) 0-15%;
(ii) vinylidene fluoride (VDF) 50-80%, perfluoroalkyl vinyl ethers (PAVE) 5-50%, tetrafluoroethylene (TFE) 0-20%;
(iii) vinylidene fluoride (VDF) 20-30%, C2-C8 non-fluorinated olefins (Ol) 10-30%, hexafluoropropene (HFP) and/or perfluoroalkyl vinyl ethers (PAVE) 18-27%, tetrafluoroethylene (TFE) 10-30%;
(iv) tetrafluoroethylene (TFE) 50-80%, perfluoroalkyl vinyl ethers (PAVE) 20-50%;
(v) tetrafluoroethylene (TFE) 45-65%, C2-C8 non-fluorinated olefins (Ol) 20-55%, vinylidene fluoride 0-30%;
(vi) tetrafluoroethylene (TFE) 32-60% mol %, C2-C8 non-fluorinated olefins (Ol) 10-40%, perfluoroalkyl vinyl ethers (PAVE) 20-40%, fluorovinyl ethers (MOVE) 0-30%;
(vii) tetrafluoroethylene (TFE) 33-75%, perfluoroalkyl vinyl ethers (PAVE) 15-45%, vinylidene fluoride (VDF) 5-30%, hexafluoropropene HFP 0-30%;
(viii) vinylidene fluoride (VDF) 35-85%, fluorovinyl ethers (MOVE) 5-40%, perfluoroalkyl vinyl ethers (PAVE) 0-30%, tetrafluoroethylene (TFE) 0-40%, hexafluoropropene (HFP) 0-30%;
(ix) tetrafluoroethylene (TFE) 20-70%, fluorovinyl ethers (MOVE) 30-80%, perfluoroalkyl vinyl ethers (PAVE) 0-50%.
Optionally, (per)fluoroelastomer (A) of the present invention also comprises recurring units derived from a bis-olefin [bis-olefin (OF)] having general formula:
wherein R1, R2, R3, R4, R5 and R6, equal to or different from each other, are H, halogen, a group RAlk or ORAlk, wherein RAlk is a branched or straight chain alkyl radical which can be partially, substantially or completely fluorinated or chlorinated; Z is a linear or branched C1-C18 alkylene or cycloalkylene radical, optionally containing oxygen atoms, preferably at least partially fluorinated, or a (per)fluoropolyoxyalkylene radical, e.g. as described in EP 661304 A (AUSIMONT SPA) 5 Jul. 1995.
The bis-olefin (OF) is preferably selected from the group consisting of those complying with formulae (OF-1), (OF-2) and (OF-3): (OF-1)
wherein j is an integer between 2 and 10, preferably between 4 and 8, and R1, R2, R3, R4, equal or different from each other, are H, F or C1-5 alkyl or (per)fluoroalkyl group;
(OF-2)
wherein each of A, equal or different from each other and at each occurrence, is independently selected from F, Cl, and H; each of B, equal or different from each other and at each occurrence, is independently selected from F, Cl, H and ORB, wherein RB is a branched or straight chain alkyl radical which can be partially, substantially or completely fluorinated or chlorinated; E is a divalent group having 2 to 10 carbon atom, optionally fluorinated, which may be inserted with ether linkages; preferably E is a —(CF2)m— group, with m being an integer from 3 to 5; a preferred bis-olefin of (OF-2) type is F2C═CF—O—(CF2)5—O—CF═CF2. (OF-3)
wherein E, A and B have the same meaning as above defined; R5, R6, R7, equal or different from each other, are H, F or C1-5 alkyl or (per)fluoroalkyl group.
The weight ratio between polymer (F) and elastomer (A) is not particularly critical, provided that it is selected by routine experiments so as to deliver a continuous thermoplastic fluoropolymer phase and a dispersed vulcanized fluoroelastomer phase in the vulcanizate (C). Generally the weight ratio polymer (F)/elastomer (A) will be comprised between 10/90 wt/wt to 50/50 wt/wt, preferably 20/80 to 40/60 wt/wt. The skilled in the art will select most appropriate weight ratio in view of target final properties of the vulcanizate (C).
The vulcanizate (C) of the invention comprises at least one ionomer (I).
Ionomer (I) generally complies with formula:
wherein:
In preferred embodiments, the ionomer (I) is an ethylene-acrylic acid copolymer comprising from 2.5 to 25% moles of recurring units derived from acrylic acid, the remained being recurring units derived from ethylene, said copolymer being at least partially salified with a metal selected from the group consisting of Na, Mg, Ca, Zn.
Ethylene-acrylic acid copolymers as above detailed can be notably obtained in the market place under trade name Aclyn® from Honeywell, as Surlyn® from DuPont de Nemours, as Iotek® from ExxonMobil, and as Primacor® from Dow Chemical Corporation.
The ionomer (I) is present in the vulcanizate (C) of the invention in an amount of 0.5 to 20% wt, preferably of 1 to 15% wt, more preferably of 3 to 10% wt, based on the weight of polymer (F).
Still, the vulcanizate (C) may comprise additional optional ingredients, such as plasticizers, extender oils, synthetic processing oils, stabilizers, processing aids, fillers, pigments, adhesives, tackifiers, and waxes. Such additional ingredients might be blended into the precursor mixture (M), or can be later compounded into the vulcanizate (C) after dynamic curing.
The invention further pertains to a precursor mixture [mixture (M)] of a thermoplastic vulcanizate fluorine-containing composition, said mixture (M) comprising:
All the features described above for components polymer (F), elastomer
(A) and ionomer (I), and for optional ingredients of the vulcanizate (C) are also applicable here as preferred embodiments of the mixture (M).
As mentioned, for obtaining the vulcanizate (C) of the present invention, the precursor mixture [mixture (M)] to be submitted to dynamic curing for obtaining the vulcanizate (C) further comprises at least one curing system for the elastomer (A).
It is thus understood that the vulcanizate (C) may thus additional comprise residues or decompositions products derived from said curing system, without this deviating from above detailed description.
The curing system can be effective for ionic curing, peroxide curing and/or mixed curing of the elastomer (A).
The amount of the curing system is not particularly limited, provided that is present in an amount effective to ensure crosslinking of the elastomer (A) within the vulcanizate (C).
A curing system for peroxide curing generally comprises at least one peroxide (generally, an organic peroxide) that is capable of generating radicals by thermal decomposition, in an amount generally of between 0.1 and 10 and preferably between 0.5 and 5 weight parts per hundred parts of the elastomer (A). Among most commonly used agents, mention can be made of: dialkyl peroxides, for instance di-tert-butyl peroxide and 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane; dicumyl peroxide; dibenzoyl peroxide; di-tert-butyl perbenzoate; bis[1,3-dimethyl-3-(tert-butylperoxy)butyl]carbonate.
Further, in addition, the curing system for peroxide curing comprises:
(a) at least one curing coagent, in an amount generally of between in an amount generally of between 0.5 and 10 and preferably between 1 and 7 weight parts per hundred parts of the elastomer (A); among these coagents, the following are commonly used: triallyl cyanurate; triallyl isocyanurate (TAIC); tris(diallylamine)-s-triazine; triallyl phosphite; N,N-diallylacrylamide; N,N,N′,N′-tetraallylmalonamide; trivinyl isocyanurate; 2,4,6-trivinyl methyltrisiloxane; bis-olefins (OF), as above detailed; triazines, such as notably those described in European patent applications EP 860436 A (AUSIMONT SPA) 26 Aug. 1998 and WO 97/05122 (DUPONT DE NEMOURS) 13 Feb. 1997; among above mentioned curing coagents, bis-olefins (OF), as above detailed, and more specifically those of formula (OF-1), as above detailed, have been found to provide particularly good results;
(b) optionally, a metallic compound, in an amounts of advantageously 1 to 15 and preferably 2 to 10 weight parts per hundred parts of the elastomer (A), selected from the group consisting of oxides and hydroxides of divalent metals, for instance Mg, Zn, Ca or Pb, optionally combined with a salt of a weak acid, for instance Ba, Na, K, Pb, Ca stearates, benzoates, carbonates, oxalates or phosphites;
(c) optionally, acid acceptors of the metal non-oxide type, such as 1,8-bis(dimethylamino)naphthalene, octadecylamine, etc.
When the vulcanizate (C) is obtained by peroxide curing, elastomer (A) preferably contains iodine and/or bromine atoms in the chain and/or at the end of the macromolecules. The introduction of these iodine and/or bromine atoms may be obtained:
A curing system for ionic curing generally comprises at least one curing agent and at least one accelerator, as well known in the art.
The amount of accelerator(s) is generally comprised between 0.05 and 5 weight parts per hundred parts of elastomer (A) (phr) and that of the curing agent typically between 0.5 and 15 phr and preferably between 1 and 6 phr.
Aromatic or aliphatic polyhydroxylated compounds, or derivatives thereof, may be used as curing agents. Among these, mention will be made in particular of dihydroxy, trihydroxy and tetrahydroxy benzenes, naphthalenes or anthracenes; bisphenols, in which the two aromatic rings are linked together via an aliphatic, cycloaliphatic or aromatic divalent radical, or alternatively via an oxygen or sulphur atom, or else a carbonyl group. The aromatic rings may be substituted with one or more chlorine, fluorine or bromine atoms, or with carbonyl, alkyl or acyl groups. Bisphenol AF is particularly preferred.
Examples of accelerators that may be used include: quaternary ammonium or phosphonium salts; aminophosphonium salts; phosphoranes; the imine compounds; etc. Quaternary phosphonium salts and aminophosphonium salts are preferred.
Instead of using the accelerator and the curing agent separately, it is also possible for the curing system for ionic curing to comprise an adduct between an accelerator and a curing agent in a mole ratio of from 1:2 to 1:5 and preferably from 1:3 to 1:5, the accelerator being one of the organic onium compounds having a positive charge, as defined above, and the curing agent being chosen from the compounds indicated above, in particular dihydroxy or polyhydroxy or dithiol or polythiol compounds; the adduct being obtained by melting the product of reaction between the accelerator and the curing agent in the indicated mole ratios, or by melting the mixture of the 1:1 adduct supplemented with the curing agent in the indicated amounts. Optionally, an excess of the accelerator, relative to that contained in the adduct, may also be present.
The following are particularly preferred as cations for the preparation of the adduct: 1,1-diphenyl-1-benzyl-N-diethylphosphoranamine and tetrabutylphosphonium; particularly preferred anions are bisphenol compounds in which the two aromatic rings are bonded via a divalent radical chosen from perfluoroalkyl groups of 3 to 7 carbon atoms, and the OH groups are in the para position.
Other ingredients optionally comprised in the curing system for ionic curing are:
i) one or more mineral acid acceptors, generally chosen from those known in the ionic curing of elastomers, preferably selected from the group consisting of oxides of divalent metals, preferably oxides of Mg, Zn, Ca or Pb, typically comprised in amounts of 1-40 phr of elastomer (A); ii) one or more basic compounds chosen from those known in the ionic curing of elastomers, commonly selected from the group consisting of hydroxides of divalent metals (preferably: Ca(OH)2, Sr(OH)2, Ba(OH)2), metal salts of weak acids, for instance Ca, Sr, Ba, Na and K carbonates, benzoates, oxalates and phosphites and mixtures of the above mentioned hydroxides with the above mentioned metal salts, typically added in amounts of from 0.5 to 10 phr of elastomer (A).
The invention further pertains to a method for manufacturing the vulcanizate (C), as above detailed, comprising dynamic curing of the mixture (M), as above detailed.
The method generally comprises heating the mixture (M) in an extruder or a mixer at a temperature above the crystalline melting point of the polymer (F), if polymer (F) is semi-crystalline, or above its glass transition temperature if polymer (F) is amorphous and vulcanizing the elastomer (A) while exerting a mixing shearing force.
The temperature is usually at least 200° C., preferably at least 250° C.
Preferred devices for carrying out the method of the invention are extruders. In such embodiments, ingredients of the mixture (M) can be pre-mixed all together and e.g. fed to the extruder through a single hopper, or can be fed to the extruder through separated feeders. It is generally preferred to add the above described curing system for the elastomer (A) through a separate feeder, which will deliver said curing system in the molten mass of elastomer (A) and fluoropolymer (F).
The vulcanizates (C) of the invention can be used as sealing material, e.g. in the chemical and semiconductor industries, and are suitable for fabricating O-rings, V-rings, gaskets and diaphragms.
In the electrical and wire/cable industries, vulcanizates (C) can be used for wire coating and wire/cable sheathing due to their flexibility, low flammability and oil, fuel and chemical resistance.
Should the disclosure of any patents, patent applications, and publications which are incorporated herein by reference conflict with the description of the present application to the extent that it may render a term unclear, the present description shall take precedence.
The invention will be now described with reference to the following examples, whose purpose is merely illustrative and not intended to limit scope of the invention.
TECNOFLON® MN FKM is a vinylidene fluoride/hexafluoropropylene elastomer having a fluorine content of 66% wt, available under the form of a micronized powder with average particle size of about 500 μm (elastomer (A1), herein after).
TECNOFLON® FOR M1 is a masterbatch made of appr. 50.0% wt of an elastomeric VDF/HFP copolymer and appr. 50.0% wt of 4,4′-[2,2,2-trifluoro-1-(trifluoromethyl)ethylidene]bisphenol (FOR M1, herein after)
TECNOFLON® FOR M2 is a masterbatch made of appr. 70.0% wt of an elastomeric VDF/HFP copolymer and appr. 30.0% wt of Benzyl (diethylamino) diphenyl phosphonium chloride (FOR M2, herein after)
ACLYN® 201 ionomer is an ethylene-acrylic acid ionomer, having an acid number of 42 mg KOH/g, commercially available from Honeywell (ionomer (I1), herein after).
HALAR® ECTFE XPH 800, which is an E/CTFE copolymer comprising about 1.5% wt of recurring units derived from perfluoropropylvinylether, commercially available from Solvay Specialty Polymers (ECTFE (F1), hereinafter).
FPA-1 is FLUOROLINK A10 perfluoropolyether macromer, having end chains of formula —CONH—C18H37, with Mw˜1800, 40% fluorine content and melting point of about 40° C.
Effect of Ionomer (I) on Curing Behaviour of Elastomer (A)
Mixtures of elastomer (A1) and curing reagents were combined with ionomer (11) for testing impact of the ionomer (I1) on cure behaviour.
Cure behaviour was characterized by Moving Die Rheometer (MDR) and Oscillating Disk Rheometer (ODR), at a temperature of 200° C., by determining the following properties:
MDR:
S′Min=Minimum elastic torque S′
S′Max=Maximum elastic torque S′
tS2=Scorch time, time for two units rise from ML (sec);
t′10=Time to 10% state of cure (sec)
t′50=Time to 50% state of cure (sec);
t′90=Time to 90% state of cure (sec)
ODR:
ML=Minimum torque (lb×in)
MH=Maximum torque (lb×in)
tS2=Scorch time, time for two units rise from ML (sec);
t′10=Time to 10% state of cure (sec)
t′50=Time to 50% state of cure (sec);
t′90=Time to 90% state of cure (sec).
Results are summarized in the following table, from which clearly results that ionomer (I1) has an advantageous effect on curing the elastomer (I1).
Manufacture of TPV Compositions
Thermoplastic vulcanizates were produced in an extruder by dynamic vulcanization, adopting the following temperature profile:
Compounds recipes and properties are summarized in the following table:
As shown above, the incorporation of Ionomer (II), in lieu of the PFPE wax PFA-1, while ensuring same processability advantages, has been demonstrated to provide excellent crosslinking behaviour, as evidenced by the dramatic reduction of swelling in DMAc, and increase in modulus.
This application claims priority to U.S. provisional application Ser. No. 61/859,913 filed on Jul. 30, 2013, the whole content of this application being incorporated herein by reference for all purposes.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2014/065879 | 7/24/2014 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 61859913 | Jul 2013 | US |
