Base-Resistant Fluoroelastomer Composition

Cross-Reference to Related Application

[0001] This application claims priority to earlier European Patent Application N° 19217570.1 , filed on December 18, 2019, the whole content of this application being incorporated herein by reference for all purposes.

Technical Field

[0002] The present invention relates to a composition based on certain base- resistant fluoroelastomer, having improved hardness which retaining high elongation at break, to a method for the manufacture of the same, and to the use thereof for producing cured parts finding utility in a variety of fields of use.

Background Art

[0003] Fluoroelastomers, specifically those based on vinylidene fluoride (VDF) as main repeat unit, made their appearance in the market space in the late 1950’s, as top-of-range sealing materials able to resist to hydrocarbons, and proven capable to withstand continuous operations up to 200°C.

[0004] It is generally understood that polymers chain comprising VDF units in the backbone are possibly subject to dehydrohalogenation in the presence of bases. Now, with increasing the production and exploitation of sour hydrocarbons (i.e. hydrocarbons including FhS or other corrosive species)

[0006] Nevertheless, especially in FKM of Type 5, the presence of a non- fluorinated olefin (ethylene) in the backbone chain, in combination with VDF, possibly hexafluoropropylene (HFP), vinyl ethers and tetrafluoroethylene (TFE) provide for fluoroelastomers which are somewhat “soft”, and which will need significant amount of reinforcing filler to achieve the hardness required in certain fields of use. Flardness of a fluororubber part, in basic terms, is the resistance of said part against intrusion and permanent deformation by a harder body. It is one property that is important for the proper specification and function of seals and other critical components notably in pressurized systems.

[0007] Indeed, when targeting hardness of exceeding 80 Shore A, the amount of carbon black required for reaching such targeted hardness may go beyond 50 parts per hundred parts of fluoroelastomer: and achievement of the targeted hardness may come with a reduction in curing rate, and with a detrimental effect on elongation at break and compression set, which are indeed key mechanical performance indicators for a sealant material.

[0008] Need is hence continuously felt in this domain for compositions based on base-resistant fluoroelastomers having hardness of 80 Shore A units or more, but retaining the outstanding sealing and elastomeric properties of the base resin.

[0009] EP3543007 is directed to a laminate including a fluoroelastomer layer and a fluororesin layer bonded to each other, wherein the fluoroelastomer layer may be formed from a blend of a fluoroelastomer and a fluororesin. Among exemplified embodiments, several examples describes fluoroelastomer

perfluoro(methyl vinyl ether) [FMVE] quinary copolymer elastomer may be used as fluororubber.

[0011] EP3026078 relates to a rubber mixture containing a fluoroelastomer and a powder based on at least one fluoropolymer, in particular PTFE, and at least one active carbon black, suitable for manufacturing fuel hoses. Summary of invention

[0012] The invention thus pertains to a composition [composition (C)] comprising:

(A) at least one fluoroelastomer [fluoroelastomer (A)] comprising:

- recurring units derived from vinylidene fluoride (VDF), said recurring units being present in an amount of at most 40 % by moles;

- recurring units derived from tetrafluorethylene (TFE), said recurring units being present in an amount of 10 to 50 % by moles;

- recurring units derived from at least one non-fluorinated alpha-olefin, said recurring units being present in an amount of 10 to 30 % by moles;

- recurring units derived from at least one (per)fluoroalkyl(oxy)vinylether, said recurring units being present in an amount of 10 to 50% by moles,

- optionally, recurring units derived from hexafluoropropylene (HFP), which when present, are in an amount up to 10 % by moles; the % being based on the total number of moles of recurring units of fluoroelastomer (A);

(B) at least one thermoplastic fluoropolymer [polymer (F)], in an amount of 10 to 40 phr, based on fluoroelastomer (A);

(C) at least one carbonaceous material [filler (C)], in an amount of at most

effective in delivering a formulation which can be cured in easier manner, and which, when transformed into cured parts, offers outstanding base resistance, delivering high hardness, e.g. of 80 Shore A or more, without detrimentally affecting sealing (C-set) and elastic (elongation at break) properties.

Description of embodiments

[0016] For the purpose of the present invention, the term “elastomeric”, when used in connection with the “fluoroelastomer (A)” is hereby intended to denote a polymer which is substantially amorphous, that is to say, has a heat of fusion of less than 2.0 J/g, preferably of less than 1.5 J/g, more preferably of less than 1.0 J/g, as measured according to ASTM D3418.

[0017] For the purpose of the present invention, the term “thermoplastic”, when used in connection with the “polymer (F)”, is hereby intended to denote a polymer which is semi-crystalline, and possesses a detectable melting point, with an associated heat of fusion of exceeding 10.0 J/g, as measured according to ASTM D3418.

[0018] The fluoroelastomer (A)

[0019] The fluoroelastomer (A) is elastomeric and is hence clearly distinguishable from polymer (F), which is thermoplastic.

[0020] The expression (per)fluoroalkyl(oxy)vinylether is intended to encompass fully fluorinated and partially fluorinated alkyl vinylethers, whereas the alkyl group may or may not comprise one or more than one ethereal oxygen atoms.

[0022] The bis-olefin (OF) is preferably selected from the group consisting of those of any of formulae (OF-1), (OF-2) and (OF-3):

(OF-1) wherein j is an integer comprised between 2 and 10, preferably between 4 and 8, and R1 , R2, R3 and R4, equal to or different from each other, are selected from the group consisting of H, F, C1-C5 alkyl groups and C1-C5 (per)fluoroalkyl groups;

(OF-2) wherein each of A, equal to or different from each other and at each occurrence, is independently selected from the group consisting of FI, F and Cl; each of B, equal to or different from each other and at each occurrence, is independently selected from the group consisting of FI, F, Cl and ORB, wherein RB is a branched or straight chain alkyl group which may be partially, substantially or completely fluorinated or chlorinated, E is a divalent group having 2 to 10 carbon atoms, optionally fluorinated, which may be inserted with ether linkages; preferably E is a -(CF2) _m - group,

\A/harain m IQ an intanar rnmnricarl hat\A/aan anH a nrafarraH hi -nlafin

The fluoroelastomer (A) may comprise cure-sites, i.e. groups which possess peculiar reactivity towards certain cure chemistry. Cure sites may be (j) iodine and/or bromine cure sites or may be (jj) nitrile or carbo- groups, or a combination (j) ⁺ (jj) thereof.

[0023] When fluoroelastomer (A) comprises iodine and/or bromine, generally, the amount of iodine and/or bromine cure site is such that the I and/or Br content is of from 0.04 to 10.0 % wt, with respect to the total weight of fluoroelastomer (A).

[0024] These iodine and/or bromine cure sites might be comprised as pending groups bound to the backbone of the fluoroelastomer (A) polymer chain or might be comprised as terminal groups of said polymer chain.

[0025] According to a first embodiment, the iodine and/or bromine cure sites are comprised as pending groups bound to the backbone of the fluoroelastomer (A) polymer chain; the fluoroelastomer (A) according to this embodiment typically comprises recurring units derived from brominated and/or iodinated cure-site comonomers selected from:

- bromo and/or iodo alpha-olefins containing from 2 to 10 carbon atoms such as bromotrifluoroethylene or bromotetrafluorobutene described, for example, in US 4035565 (DU PONT ) 12/07/1977 or other compounds bromo and/or iodo alpha-olefins disclosed in US 4694045 (DU PONT ) 15/09/1987 ;

- iodo and/or bromo fluoroalkyl vinyl ethers (as notably described in patents US 454662 , US 4564662 (MINNESOTA MINING ) 14/01/1986 and EP 199138 A (DAI KIN IND LTD ) 29/10/1986 ).

atoms, while x and y are integers between 0 and 2, with 1 < x+y < 2 (see, for example, patents US 4243770 (DAI KIN IND LTD ) 6/01/1981 and US 4943622 (NIPPON MEKTRON KK ) 24/07/1990 ); and

- alkali metal or alkaline-earth metal iodides and/or bromides, such as described notably in patent US 5173553 (AUSIMONT SRL) 22/12/1992 .

[0027] Advantageously, for ensuring acceptable reactivity it is generally understood that the content of iodine and/or bromine in the fluoroelastomer (A) may be of at least 0.05 % wt, preferably of at least 0.06 % weight, with respect to the total weight of elastomer (F).

[0028] On the other side, amounts of iodine and/or bromine not exceeding preferably 7 % wt, more specifically not exceeding 5 % wt, or even not exceeding 4 % wt, with respect to the total weight of fluoroelastomer (A), may be those generally selected for avoiding side reactions and/or detrimental effects on thermal stability.

[0029] When fluoroelastomer (A) comprises nitrile or carbo-groups, generally, the fluoroelastomer (A) comprises from 0.1 to 10.0 % moles, with respect to total moles of recurring units of elastomer (F), of recurring units derived from at least one of:

- cure-site containing monomers having at least a nitrile group [monomer (CS-N)];

- cure-site containing monomers having at least a carbo-group [monomer (CS-C)] selected from the group consisting of carboxylic groups -COOH; carboxylate groups -COOX _a , with X _a being a monovalent metal or an ammonium group; carboxamide group -CONFh; and alkoxycarboxylic

(0CF ₂ CFX ^CN )m’-0-CF ₂ — CF(CF ₃ )-CN, with X ^CN being F or CF ₃ , m’ being 0, 1, 2, 3 or 4.

Specific examples of cure-site containing monomers of type CS-N1 and CS-N2 suitable to the purposes of the present invention are notably those described in patents US 4281092 (DU PONT ) 28/07/1981 , US 4281092 (DU PONT ) 28/07/1981 , US 5447993 (DU PONT ) 5/09/1995 and US 5789489 (DU PONT ) 4/08/1998 . Preferred cure-site monomer (CS-N) is perfluoro(8-cyano-5-methyl-3,6-dioxa-1 -octene) of formula: CF ₂ =CF-0- CF ₂ -CF(CF ₃ )-0-CF ₂ -CF ₂ -CN (8-CNVE).

[0031] Among cure-site containing monomers of type (CS-C), as above detailed, preferred monomers are (per)fluorinated and are especially those selected from the group consisting of:

(CS-C1) perfluorovinyl ethers containing carbo-groups of formula CF ₂ =CF- (OCF ₂ CFX ^c )m-0-(CF ₂ )n-Rcox, with X ^c being F or CF ₃ , m being 0, 1 , 2, 3 or 4; n being an integer from 1 to 12, and Rcox being selected from the group consisting of carboxylic groups -COOFI; carboxylate groups -COOX _a , with X _a being a monovalent metal or an ammonium group; carboxamide group -CONH ₂ ; and alkoxycarboxylic group -COO-R _H , with RH being a (fluoro)(hydro)carbon group, preferably a Ci-C ₃ alkyl group ;

(CS-C2) perfluorovinyl ethers containing carbo-groups of formula CF ₂ =CF- (0CF ₂ CFX ^c )m-0-CF ₂ — CF(CF ₃ )-RCO _X , with m’ being 0, 1 , 2, 3 or 4, and X ^c and Rcox having the meaning as defined for (CSC-1).

[0032] Most valuable results have been obtained with fluoroelastomers (A) comprising iodine and/or bromine cure sites, and more specifically, with

selected from the group consisting or ethylene and propylene, in an amount of 10 to 30 % by moles, preferably from 15 to 28 % moles, preferably recurring units derived from ethylene in an amount of 15 to 25% moles;

- recurring units derived from at least one (per)fluoroalkyl(oxy)vinylethers in an amount of 10 to 50 % moles, preferably in an amount of 15 to 35 % moles, wherein the said (per)fluoroalkyl(oxy)vinylethers is preferably selected from the group consisting of:

(i) perfluoroalkylvinylethers (PAVE) of formula CF2=CFORfi, wherein Rn is a Ci-C ₆ perfluoroalkyl group, such as CF3 (PMVE), C2F5 or C3F7, and

(ii) perfluorooxyalkylvinylethers of formula CF2=CFOXo, wherein Xo is a Ci- C12 perfluorooxyalkyl group comprising one or more than one ethereal oxygen atom, including notably perfluoromethoxyalkylvinylethers of formula CF2=CF0CF20Rf2, with Rf2 being a C1-C3 peril uoro(oxy)alkyl group, such as -CF2CF3, -CF2CF2-O-CF3 and -CF3; and is more preferably a PAVE, even more preferably PMVE;

- optionally, recurring units derived from a bis-olefin (OF), as described above, which, when present, are in an amount up to 1.0% by moles, preferably up to 0.5% by moles;

- optionally, recurring units derived from hexafluoropropylene (HFP), which when present, are in an amount up to 10 % by moles; the % being based on the total number of moles of recurring units of fluoroelastomer (A).

[0034] Generally, fluoroelastomer (A) comprises substantially no other units

- recurring units derived from perfluoromethylvinylether (PMVE) in an amount of 20 to 35 % moles; and

- recurring units derived from tetrafluoroethylene (TFE) in an amount of 35 to 45 % by moles, and

- optionally, recurring units derived from a bis-olefin (OF), as described above, in an amount of up to 0.2 % by moles, the % being based on the total number of moles of recurring units of fluoroelastomer (A).

[0036] Fluoroelastomer (A) generally possesses a Mooney viscosity (ML 1+10 min at 121 °C) of at least 15 and at most 70, preferably of at least 20 and at most 40.

[0037] Polymer (F)

[0038] Polymer (F) is a fluoropolymer, that is to say a polymer comprising advantageously recurring units derived from one or more than one fluoromonomer, preferably selected from the group consisting of:

(a) C2-C8 perfluoroolefins such as tetrafluoroethylene (TFE), hexafluoropropylene (HFP);

(b) hydrogen-containing C2-C8fluoroolefins, such as vinylidene fluoride (VDF), vinyl fluoride, trifluoroethylene (TrFE), hexafluoroisobutylene (HFIB), perfluoroalkyl ethylenes of formula CH2=CH-R _fi , wherein Rn is a C1-C6 perfluoroalkyl group;

(c) C2-C8 chloro- and/or bromo-containing fluoroolefins such as chlorotrifluoroethylene (CTFE);

(d) (per)fluoroalkyl(oxy)vinylethers, as detailed above; and

hydrogenated monomer, including notably ethylene, propylene, (meth)acrylic monomers, styrenic monomers.

[0039] More specifically, polymer (F) may be selected from the group consisting of:

- VDF-based polymers [polymer (FVDF)] comprising, preferably essentially consisting of, recurring units derived from vinylidene fluoride (VDF) and optionally from one or more than one additional fluorinated monomer different from VDF, e.g. HFP, TFE or CTFE, and optionally from a hydrogenated monomer, as above detailed, e.g. a (meth)acrylic monomer, whereas the amount of recurring units derived from VDF is of 80 to 100 % moles, based on the total moles of recurring units of polymer (FVDF);

- TFE-based polymers [polymers (FTFE)] comprising, preferably essentially consisting of, recurring units derived from tetrafluoroethylene (TFE), and optionally from an additional perfluorinated monomer different from TFE, whereas the amount of recurring units derived from TFE is of 75 to 100 % moles, based on the total moles of recurring units of block (B);

- E(C)TFE-based polymers [polymer (FE/(OTFE)] comprising, preferably essentially consisting of, recurring units derived from ethylene; and recurring units derived from at least one of CTFE and TFE, possibly in combination with an additional monomer.

[0040] The polymer (FVDF) preferably comprises :

(a’) at least 80 % by moles, preferably at least 85 % by moles, more preferably at least 90 % by moles of vinylidene fluoride (VDF);

(b’) optionally from 0.1 to 15%, preferably from 0.1 to 12%, more

[0041] As non-limitative examples of the polymer (FVDF) useful in the present invention, mention can be notably made of homopolymers of VDF, VDF/TFE copolymers, VDF/TFE/HFP copolymers, VDF/TFE/CTFE copolymers, VDF/TFE/TrFE copolymers, VDF/CTFE copolymers, VDF/HFP copolymers, VDF/TFE/HFP/CTFE copolymers, VDF/TFE/perfluorobutenoic acid copolymers, VDF/TFE/maleic acid copolymers and the like.

[0042] Most preferably the polymer (FVDF) is selected from the group consisting of VDF homopolymers and copolymers of VDF with 0.1 to 10% by moles of a fluorinated comonomer selected from the group consisting of chlorotrifluoroethylene (CTFE), hexafluoropropene (HFP), tetrafluoroethylene (TFE), trifluoroethylene (TrFE) and mixtures thereof.

[0043] The polymer (FVDF) has a melting point advantageously of at least 120°C, preferably at least 135°C, more preferably at least 150°C.

[0044] The polymer (FVDF) has a melting point advantageously of at most 190°C, preferably at most 185°C, more preferably at most 180°C.

[0045] The melting point (T _m 2) is determined by DSC, at a heating rate of 10° C/min, according to ASTM D 3418.

[0046] With the aim of optimizing contribution to mechanical properties related to the crystalline structure of the polymer chain, the polymer (FVDF) has preferably a heat of fusion of at least 10 J/g, preferably of at least 20 J/g, most preferably of 40 J/g.

[0047] The heat of fusion is determined by DSC, at a heating rate of 10°C/min, according to ASTM D 3418.

perfluoroalkylvinylethers, perfluoroalkylethylenes (such as perfluorobutylethylene), perfluorodioxoles, vinylidene fluoride. Among them, a particularly preferred comonomer is perfluoropropylvinylether of formula CF2=CFO-C3F7.

[0050] Non limiting examples of hydrogenated comonomers, are those having the general formula: CFh=CFI-(CFl2)nRi wherein Ri =OR2, or -(0)tC0(0) _p R2 wherein t and p are integers equal to 0 or 1 and R2 is FI or a hydrogenated linear or branched alkyl or cycloalkyl radical having from 1 to 20 carbon atoms, optionally containing heteroatoms and/or chlorine atoms, the heteroatoms preferably being O or N; R2 optionally contains one or more functional groups, preferably selected from OFI, COOFI, epoxide, ester and ether, R2 may optionally contain double bonds; n is an integer in the range 0-10. Preferably R2 is an alkyl radical having from 1 to 10 carbon atoms containing hydroxyl functional groups and n is an integer in the range 0-5. [0051] Preferred hydrogenated comonomers are selected from the following classes:

- acrylic monomers having the general formula: CFh=CFI-C0-0-R ₂ , wherein R2 is selected from ethylacrylate, n-butylacrylate, acrylic acid, hydroxyalkylacrylates, such as hydroxyethylacrylate, hydroxypropylacrylate, (hydroxy)ethylhexylacrylate;

- vinylether monomers having the general formula: CFh=CFI-0-R ₂ , wherein R2 is selected from propylvinylether, cyclohexylvinylether, vinyl-4-hydroxybutylether;

- vinyl monomers of the carboxylic acid having the general formula:

(c’) from 0 to 30%, preferably from 0.1 to 15 % by moles, based on the total amount of monomers (a) and (b), of one or more fluorinated and/or hydrogenated comonomer(s), different from E and CTFE.

[0053] All features described above in connection with polymer (FE/(OTFE) are applicable, mutatis mutandis, to the ECTFE polymer.

[0054] ECTFE polymers generally have a melting temperature not exceeding 220 °C, preferably not exceeding 200°, even not exceeding 198°C, preferably not exceeding 195°C, more preferably not exceeding 193°C, even more preferably not exceeding 190°C. The ECTFE polymer has a melting temperature of advantageously at least 120°C, preferably of at least 130° C, still preferably of at least 140°C, more preferably of at least 145°C, even more preferably of at least 150°C.

[0055] The melting temperature is determined by Differential Scanning

Calorimetry (DSC) at a heating rate of 10°C/min, according to ASTM D 3418.

[0056] While polymer (FTFE) may be a homopolymer of TFE, it is nevertheless preferred for polymer (FTFE) to be a melt-processable tetrafluoroethylene copolymer, more particularly of a polymer formed of tetrafluoroethylene (TFE) copolymer with one or more perfluorinated comonomers [comonomer (F)]. For the purpose of the present invention, a “melt- processible” polymer refers to a polymer that can be processed (i.e. fabricated into shaped articles of whichever shape) by conventional melt extruding, injecting or coating means. This generally requires that the melt viscosity of the polymer at the processing temperature be no more than

[0060] Among suitable comonomers (F), mentions can be made of:

- C ₃ -C ₈ perfluoroolefins, e.g. hexafluoropropene (HFP), hexafluoroisobute- ne;

- CF ₂ =CFOR _f perfluoroalkylvinylethers (PAVE), wherein R _f is a C ₁ -C ₆ perfluoroalkyl, e.g., -CF3, -C ₂ F5, or -C3F7;

- CF ₂ =CFOX perfluorooxyalkylvinylethers wherein X is a C ₁ -C ₁₂ perfluorooxyalkyl having one or more ether groups; and

- perfluorodioxoles.

[0061] Preferably, said comonomer (F) is selected from the following comonomers:

- PAVEs of formula CF ₂ =CFOR _fi , wherein Rn is selected from -CF3, -C ₂ F5, and -C3F7, namely, perfluoromethylvinylether (PMVE of formula CF ₂ =CFOCF3), perfluoroethylvinylether (PEVE of formula CF ₂ =CFOC ₂ F5 ), perfluoropropylvinylether (PPVE of formula CF ₂ =CFOC3F7), and mixtures thereof;

- perfluoromethoxy vinyl ether (MOVE) of general formula CF ₂ =CFOC- F ₂ 0R _f2 , wherein R _f2 is a linear or branched C ₁ -C6 perfluoroalkyl group, cyclic C5-C6 perfluoroalkyl group, a linear or branched C ₂ -C6 perfluoroxyalkyl group; preferably, R _{f2 i} s -CF ₂ CF3 (MOVE1), -CF ₂ CF ₂ OCF3 (MOVE2), or -CF ₃ (MOVE3); and

- perfluorodioxoles having the following formula:

perfluoromethylvinylether;

(b) from 0 to 3 % by weight of recurring units derived from one or more than one fluorinated comonomer different from perfluoromethylvinylether and selected from the group consisting of perfluoroalkylvinylethers as detailed above, and perfluorooxyalkylvinylethers as detailed above; preferably derived from perfluoroethylvinylether and/or perfluoropropylvinylether ;

(c) recurring units derived from tetrafluoroethylene, in such an amount that the sum of the percentages of the recurring units (a), (b) and (c) is equal to 100 % by weight.

[0063] Carbonaceous material

[0064] Within the context of the present invention, the expressions

"carbonaceous material" and “filler (C)” are intended to denote all those materials which essentially consist of carbon. It is understood that said carbonaceous materials might comprise reduced amounts of other elements (e.g. H, O, N, S...), without this significantly affecting the physico-chemical properties of the carbonaceous material itself.

[0065] Among carbonaceous materials suitable for the purposes of the invention, mention can be notably made of carbon blacks, carbon fibers, diamond like carbon, graphites, fullerenes, including spherical fullerenes and carbon nanotubes.

[0066] The expression “carbon black” is intended to denote powdered form of highly dispersed, mostly amorphous elemental carbon. Carbon black is generally available as a finely divided, colloidal material in the form of

such as heavy petroleum distillates and residual oils, coal-tar products, natural gas and acetylene. The expression “carbon black” thus embraces notably acetylene black, channel black, furnace black, lamp black, thermal black. Acetylene black is the type of carbon black derived from the burning of acetylene. Channel black is made by impinging gas flames against steel plates or channel irons (from which the name is derived), from which the deposit is scraped at intervals. Furnace black is the term generally applied to carbon black made in a refractory-lined furnace. Lamp black, the properties of which are markedly different from other carbon blacks, is made by burning heavy oils or other carbonaceous materials in closed systems equipped with settling chambers for collecting the solids. Thermal black is produced by passing natural gas through a heated brick checkerwork where it thermally cracks to form a relatively coarse carbon black. Over 90% of all carbon black produced today is furnace black. Carbon black is available commercially from numerous suppliers such as Cabot Corporation.

[0067] The expression “Diamond-like carbon (DLC)”, as used therein, encompasses all forms of amorphous carbon materials containing significant amounts (e.g. > 50 %) of sp ³ hybridized carbon atoms. As a result, DLC materials typically display some of the unique properties of natural diamond. It is well-known that natural diamond can be found in two crystalline polytypes. The usual one has its carbon atoms arranged in a cubic lattice, while the very rare one (lonsdaleite) has a hexagonal lattice. In DLC materials, these polytypes are typically present at the nanoscale

forms of DLC to reduce production expenses, but at the cost of decreasing the service lifetimes of the articles being coated. The various forms of DLC can be applied to almost any material that is compatible with a vacuum environment.

[0068] The term “graphites” is intended to encompass the low density allotropes of carbon (C), whose structure consists of layered hexagonal rings of sp ² - hybridised carbon atoms. These layers are notably held together by weak Van der Waals type forces resulting from the interactions between clouds of delocalised p electrons from each of the layers.

[0069] The term “fullerene” encompasses carbon molecules (notably different from graphite and diamond), consisting of a spherical, ellipsoid, or cylindrical arrangement of carbon atoms bound by sp ² bonds, under the form of predominant linked hexagonal rings of carbon atoms, but also pentagonal or sometimes heptagonal rings that prevent said assembly from being planar.

[0070] Spherical fullerenes are often called "buckyballs" whereas cylindrical fullerenes are known as "buckytubes", or "carbon nanotubes (CNT)".

[0071] Either single-walled carbon nanotubes (SWCN) or multi-walled carbon nanotubes (MWCN) can be used to the purpose of the invention. CNTs may have diameters ranging from about 0.6 nanometers (nm) for a single wall carbon nanotube (SWNT) up to 3 nm, 5 nm, 10 nm, 30 nm, 60 nm or 100 nm for a SWNT or a multiple-wall carbon nanotube (MWNT). A CNT may range in length from 50 nm up to 1 millimeter (mm) , 1 centimeter (cm) , 3 cm, 5 cm, or greater. A CNT will typically have an aspect ratio of

[0075] The polymer (F) is preferably included in an amount of at least 12 phr, preferably at least 15 phr; and/or of at most 30 phr, preferably at most 25 phr, based on fluoroelastomer (A).

[0076] As per filler (C), while lower boundary will be selected depending on the targeted Shore A hardness, it is generally understood that composition (C) will comprise filler (C) in an amount of at least 5 phr, preferably at least 8 phr; further, excellent balance in Shore A hardness and sealing/elongation at break performances have been achieved when the amount of filler (C) was of at most 45 phr, preferably at most 42 phr, more preferably at most 40 phr, and even more preferably at most 38 phr.

[0077] Depending on the cure mechanism used for processing composition (C) into cured parts, composition (C) comprises advantageously additional ingredients, as necessary for achieving effective curing.

[0078] Best results have been obtained when composition (C) was a peroxide curable composition, i.e. a composition further comprising:

- at least one organic peroxide [peroxide (O)];

- at least one polyunsaturated compound [compound (U)]; and

- at least one basic compound [compound (B)].

[0079] The choice of the said peroxide (O) is not particularly critical provided that the same is capable of generating radicals. Among most commonly used peroxides, mention can be made of:

- di(alkyl/alryl) peroxides, including for instance di-tert-butyl peroxide, 2,5- dimethyl-2,5-bis(tert-butylperoxy)hexane, di(t- butylperoxyisopropyl)benzene, dicumyl peroxide;

hexylperoxyisoproprylcarbonate, t-butylperoxyisopropylcarbonate,

- perketals such as 1 , 1-bis(tert-butylperoxy)cyclohexane and 2, 2- bis(tertbutylperoxy)butane;

- ketone peroxides such as cyclohexanone peroxide and acetyl acetone peroxide;

- organic hydroperoxides such as cumene hydroperoxide, tert-butyl hydroperoxide, methylethylketone peroxide (otherwise referred to as 2-[(2- hydroperoxybutan-2-yl)peroxy]butane-2-peroxol) and pinane hydroperoxide;

- oil-soluble azo initiators such as 2, 2'-azobis (4-methoxy-2. 4-dimethyl valeronitrile), 2, 2'-azobis (2.4-dimethyl valeronitrile), 2,2'- azobis(isobutyronitrile), 2, 2'-azobis(2-cyano-2-butane), dimethyl-2, 2'- azobisdimethyli sobutyrate, dimethyl-2, 2'-azobis(2-methylpropionate), 2,2'- azobis(2-methylbutyronitrile), 1 ,1'-azobis(cyclohexane-l-carbonitrile), 2, 2'- azobis[N-(2-propenyl)-2-methylpropionamide], 1 -[(1 -cyano-1 -methyl ethyl)azo]formamide, 2, 2'-azobis(N-cyclohexy1 -2-methylpropionamide), 2,2'-azobis(i sobutyronitrile), 2,2'-azobis(2-cyano-2-butane), dimethyl-2, 2'- azobisdimethylisobutyrate, 1 ,1'-azobis(cyclohexanecarbonitrile), 2-(t- butylazo)-2-cyanopropane, 2,2'-azobis[2-methyl-N-(1, 1)- bis(hydroxymethyl)-2-hydroxyethyl]propionamide, 2, 2'-azobis[2-methyl-N- hydroxyethyl]-proprionamide, 2, 2'-azobis(N, N'- dimethyleneisobutyramine), 2, 2'-azobis(2-methyl-N-[1 ,1- bis(hydroxymethyl)-2-hydroxyethyl] propionamide), 2,2'-azobis(2-methyl- N-[1 ,1-bis(hydroxymethyl) ethyl] proprionamide), 2, 2'-azobis[2-5 methyl-

[0082] Compounds (U) may be selected from compounds comprising two carbon- carbon unsaturations, compounds comprising three carbon-carbon unsaturations and compounds comprising four or more than four carbon- carbon unsaturations.

[0083] Among compounds (U) comprising two carbon-carbon unsaturations, mention can be made of bis-olefins [bis-olefin (OF)], as above detailed, preferably selected from those complying with any of formulae (OF-1), (OF-2) and (OF-3), as above detailed.

[0084] Among compounds (U) comprising three carbon-carbon unsaturations, mention can be made of:

- tri-substuituted cyanurate compounds of general formula: wherein each of R _cy , equal to or different from each other and at each occurrence, is independently selected from FI or a group -R _rcy or-OR _rcy , with R _rcy being C ₁ -C5 alkyl, possibly comprising halogen(s), and each of J _cy , equal to or different from

wherein each of Risocy, equal to or different from each other and at each occurrence, is independently selected from H or a group -Rrisocy or-ORrisocy , with Rrisocy being C1-C5 alkyl, possibly comprising halogen(s), and each of Jisocy, equal to or different from each other and at each occurrence, is independently selected from a bond or a divalent hydrocarbon group, optionally comprising heteroatoms; tri-substuituted isocyanurate compounds include notably preferred triallyl isocyanurate (otherwise referred to as “TAIC”), trivinyl isocyanurate, with TAIC being the most preferred;

- tri-substituted triazine compounds of general formula:

include notably compounds disclosed in EP 0860436 A (AUSIMONT SPA) 26/08/1998 and in WO 97/05122 (DU PONT) 13/02/1997 ;

- tri-substituted phosphite compounds of general formula: wherein each of R _Ph , equal to or different from each other and at each occurrence, is independently selected from H or a group -R _rph or-OR _rph , with R _rph being C1-C5 alkyl, possibly comprising halogen(s), and each of J _Ph , equal to or different from each other and at each occurrence, is independently selected from a bond or a divalent hydrocarbon group, optionally comprising heteroatoms; tri- substituted phosphite compounds include notably preferred tri-allyl phosphite;

- tri-substituted alkyltrisiloxanes of general formula:

divalent hydrocarbon group, optionally comprising heteroatoms; tri- substituted alkyltrisiloxanes compounds include notably preferred 2,4,6- trivinyl methyltrisiloxane and 2,4,6-trivinyl ethyltrisiloxane;

- N,N-disubstituted acrylamide compounds of general formula: wherein each of R _an , equal to or different from each other and at each occurrence, is independently selected from H or a group — Rran or— ORran, with Rran being C1-C5 alkyl, possibly comprising halogen(s), and each of J _an , equal to or different from each other and at each occurrence, is independently selected from a bond or a divalent hydrocarbon group, optionally comprising heteroatoms; N,N-disubstituted acrylamide compounds include notably preferred N,N-diallylacrylamide.

[0085] Among compounds (U) comprising four or more carbon-carbon unsaturations, mention can be made of tris(diallylamine)-s-triazine of

preferably from 1 to 10 weight parts per 100 parts by weight of fluoroelastomer (A).

[0088] The said at least one basic compound [compound (B)] may be selected from the group consisting of:

(a) one or more than one metallic basic compound, in amounts generally of from 0.5 to 15 phr, and preferably of from 1 to 10 phr, relative to 100 weight parts of fluoroelastomer (A); metallic basic compounds are generally selected from the group consisting of (j) oxides or hydroxides of divalent metals, for instance oxides or hydroxides of Mg, Zn, Ca or Pb, and (jj) metal salts of a weak acid, for instance Ba, Na, K, Pb, Ca stearates, benzoates, carbonates, oxalates or phosphites;

(b) one or more than one acid acceptor which is not a metallic basic compound, in amounts generally of from 0.5 to 15 phr, and preferably of from 1 to 10 phr, relative to 100 weight parts of fluoroelastomer (A); these acid acceptors are generally selected from nitrogen-containing organic compounds, such as 1 ,8-bis(dimethylamino)naphthalene, octadecylamine, etc., as notably described in EP 708797 A (DU PONT ) 1/05/1996.

[0089] Composition (C) generally comprises polymer (F) dispersed in the matrix of fluoroelastomer (A) in a manner such that phase-separated and/or not cohered domains of polymer (F) having a size exceeding 300 nm are substantially absent.

[0090] The expression “substantially absent” in combination with the amount of phase separated domains of polymer (F) of size exceeding 300 nm is to be understood to mean that a SEM magnification of a fractured surface of

words, this method corresponds to the measurement by a slide gauge of inclusions or physically separated domains.

[0092] Composition (C) generally comprises polymer (F) essentially under the form of phase-separated domains comprised in a matrix of fluoroelastomer (A) having an averaged size of at most 300 nm, preferably at most 280 nm, more preferably at most 200 nm; and/or at least 10 nm, preferably at least 15 nm, more preferably at least 20 nm.

[0093] Such dispersion of polymer (F) in the matrix of fluoroelastomer (A) is advantageously achieved through blending polymer (F) under the form of latex and fluoroelastomer (A) under the form of latex, followed by co coagulation.

[0094] Method of making composition (C)

[0095] The invention further pertains to a method of making the composition (C) as above detailed, in particular blending a latex of fluoroelastomer (A) and a latex of polymer (F), followed by co-coagulation and mixing with filler (C). [0096] In particular, the method of the invention comprises: a Step (A) of mixing:

- an aqueous latex of at least one fluoroelastomer (A), as described above; and

- an aqueous latex of at least one polymer (F), as described above; so as to obtain a latex mixture [mixture (L)]; and a Step (B) of coagulating the said mixture (L), so as to obtain a coagulated blend (B); and a Step (C) of mixing the filler (C), and optionally any further ingredient, into

techniques include surfactant-assisted emulsion polymerization, in particular in the presence of fluorinated surfactant, and including micro emulsion polymerization, in a fluorinated dispersed phase stabilized with appropriate surfactant, in particular in micro-droplets of a fluorinated perfluoropolyether oil stabilized with fluorinated surfactant, e.g. perfluoropolyether carboxylate salts. It is further understood that alternative emulsion polymerization techniques which are not using any fluorinated surfactant can equally be used for providing suitable latexes of fluoroelastomer (A) and polymer (F).

[00100] Aqueous medium is predominantly composed of water, although it may comprise minor amount of other components, including e.g. residues of initiators, (fluoro)surfactants, and/or other auxiliaries which may derive from the manufacture of the latex itself, in an amount of generally less than 5 %wt., with respect to the total weight of the latex.

[00101] Generally, the latex of fluoroelastomer (A) comprises the fluoroelastomer (A) in an amount of at least 15 %wt., preferably at least 20%wt., more preferably at least 25 %wt., and/or in an amount of at most 60%wt., preferably at most 50 %wt., more preferably at most 40 %wt., with respect to the total weight of latex. Similarly, the latex of polymer (F) generally comprises the polymer (F) in an amount of at least 15 %wt., preferably at least 20%wt., more preferably at least 25 %wt., and/or in an amount of at most 60%wt., preferably at most 50 %wt., more preferably at most 40 %wt., with respect to the total weight of latex.

[00102] The Step (A) of mixing

[0106] Mixing is carried out generally at a temperature of at least 5°C, preferably of at least 15 °C, more preferably at least 20°C and/or at a temperature of at most 80°C, preferably at most 70°C, more preferably at most 60°C, even more preferably at most 50°C.

[0107] It is nevertheless generally preferred to accomplish mixing around about room temperature, or generally between 15 and 30°C.

[0108] The method comprises mixing a latex of polymer (F) and a latex of fluoroelastomer (F) in such amounts that the latex-blended mixture (L) comprises the respective amounts of fluoroelastomer (A) and polymer (F), as detailed above in connection with target composition (C).

[0109] The Step (B) of coagulating

[0110] In second step of the method of the invention, the mixture (L) can be coagulated by standard techniques.

[0111] The mixture (L) can be coagulated through addition of an electrolyte or through any electrolyte-free techniques of coagulation which are known to those of ordinary skills in the art.

[0112] Among electrolyte-free techniques, mention can be made of coagulation through high pressure compression/decompression, e.g. by forced flow through a series of restrained openings; of coagulation under high shear, e.g. under extremely vigorous stirring; and of coagulation by freeze/thaw techniques.

[0113] Coagulation under high shear may be effected sequentially after mixing, by merely increasing shear stress applied by means of the mixing device used in Step (A).

[0117] A coagulate is so generated during this coagulation step, whose separation from the dispersing medium may be effected by using conventional techniques such as flotation, filtration, centrifugation, decantation, or a combination of these techniques.

[0118] The coagulate so recovered is generally dried using standard techniques, so as to advantageously remove residual moisture.

[0119] A blend (B) is hence so obtained.

[0120] The Step (C) of mixing the filler (C), and optionally any further ingredient

[0121] Mixing filler (C) and any possible further ingredients (such as, as explained above, curing ingredients, such as peroxide, unsaturated compound and basic compound) is generally achieved by mixing in a roll mill or in an internal mixer.

[0122] Method of processing composition (C)

[0123] The invention also pertains to a method of processing composition (C) for making cured articles.

[0124] The composition (C) can be processed, e.g. by moulding (injection moulding, compression moulding), calendering, or extrusion, into the desired shaped article, which is advantageously subjected to vulcanization (curing) during the processing itself and/or in a subsequent step (post treatment or post-cure), advantageously transforming the relatively soft, weak, fluoroelastomeric uncured composition into a finished cured article made of non-tacky, strong, insoluble, chemically and thermally resistant cured fluoroelastomer material.

[0125] The method hence typically comprises processing the composition (C), as

for Oil & Gas industry, and oil seals or maybe piping and tubings, in particular sealing parts or other items includes in semi-conductor manufacturing devices.

[0127] 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.

[0128] The invention will be now described in more details with reference to the following examples, whose purpose is merely illustrative and not intended to limit the scope of the invention.

[0129] Raw materials

[0130] Tecnoflon® BR9171 latex is a latex (28% wt solids) of an ASTM D1418 FKM having a fluorine content of 66.3 % and a Mooney viscosity ML (1+10’) at 121 °C of 30 MU.

[0131] PVDF (homopolymer) latex, and MFA (98/2 wt/wt TFE/PMVE) latex having 25% wt solids

[0132] Different C-blacks (N326 HAF, N550 FEF, N990 MT) commercially available from Cabot were used.

[0133] Luperox® 101 XL 45 is a 45% active dispersion of 2,5 Dimethyl 2,5 Di(tert-butylperoxyl) hexane on a calcium carbonate filler.

[0134] Drimix® TAIC 75 is supported triallyl isocyanurate (75% supported on synthetic calcium silicate).

[0135] Struktol® WS 280 is a processing additive based on organosilicones, commercially available from Struktol.

blades stirrer, at a stirring speed of 300 rpm.

The blend obtained by mixing said latexes was then dripped in a glass vessel at a temperature of 60°C, containing 15 litres of water in which 60 g of AI ₂ (S0 ₄ )3 have been previously dissolved. During dripping, stirring was kept constant at 550 rpm. In this phase the blend coagulated.

At the end of dripping, stirring was continued for 5 minutes. The obtained co-coagulated solid was then separated from the aqueous phase and washed with clean demineralized water for four times.

After washing, the obtained material was dried at 90°C for 16 h in drying oven.

Specimens of so obtained blend were submitted to SEM microscopy analysis, showing substantial absence of domains phase-separated/not cohered with sizes of 300 nm or more.

Such blends were further formulated with carbon black and curing ingredients, as detailed in Table 1 below. In a similar manner, in Ex. 5C, bare fluoroelastomer, deprived of thermoplastic fluoropolymer filler, was formulated in a similar manner, but using increased amount of Carbon black, so as to match the targeted Shore A hardness of about 90 Shore A. Table 1

[0139] P N990 MT C-black; n N550 FEF C-black; <“ ^* > blend of 20 phr of N326 HAF C-black and 30 phr of N990 MT C-black.

[0140] Characterization of the blends

[0141] Cure behaviour was characterized by Moving Die Rheometer (MDR), in conditions as specified below, by determining the following properties:

ML = Minimum torque (lb x in)

MH = Maximum torque (lb x in) t_02 = Scorch time, time for two units rise from ML (sec); t_50 = Time to 90% state of cure (sec); t_90 = Time to 90% state of cure (sec).

Materials obtained from Examples 1, 2, 3 and 4, and comparative Ex. 5C were molded with the compression molding method in 2 mm thick plaques, by hot pressing at 170°C for 5 minutes under a pressure of 25 MPa.

[0142] The tensile properties have been determined on specimens punched out from the plaques, according to the ASTM D412 Standard at 23°C.

TS is the tensile strength in MPa;

EB is the elongation at break in %.

The Shore A hardness (3") (HDS) has been determined on 3 pieces of plaque piled according to the ASTM D 2240 method.

[0143] Compression Set (C-Ste) was determined according to ASTME D395, at 9nn°r. nn hm ·G¾I

[0146] Data summarized above clearly demonstrate that the incorporation of both polymer (F) and filler (C) in the above detailed amounts in a matrix of base-resistant fluoroelastomer (A) is such to provide for a composition possessing easier processability, outstanding curing behaviour and possessing a better balance of hardness/elastomeric performances. Indeed, inventive compositions, possessing all a Shore A hardness of around 90 units, were found to be endowed with significantly higher EB, and lower residual deformation (C-Set) when compared to traditional base resistant fluororubber formulations, having same Shore A hardness, achieved through the incorporation of increased amounts of C-black.

[0147] Specimens according to DIN53504 S2 of cured fluororubbers of Ex. 4 and Ex. 5C have been tested for their chemical resistance, by measuring TS,

[0149] Data above well demonstrate that the composition according to the present invention, while comprising less carbon black and more polymer- fraction (because of the presence of polymer(F)) retains nevertheless essentially same chemical resistance performances as the reference base resistant fluororubber.