Curable fluoroelastomer composition

Abstract

The present invention relates to certain fluoroelastomer compositions comprising (i) a fluoroelastomer (fluoroelastomer A) obtained from an emulsion polymerization process carried out in the absence of fluorinated surfactants, the present invention relates to a composition comprising (i) one or more fluorinated monomers, (ii) one or more organic peroxides, (iii) one or more curing aids, (iv) one or more fatty acid salts, comprising iodine and / or bromine atoms and having a backbone comprising from 40% to 80% by mole of recurring units derived from vinylidene fluoride (VDF), from 20% to 60% by mole of recurring units derived from one or more additional fluorinated monomers different from VDF, (ii) one or more organic peroxides, (iii) one or more curing aids, (iv) one or more fatty acid salts. The composition yields a cured part with improved c-set performance relative to the same composition without the addition of a fatty acid salt.

Description

TECHNICAL FIELD

[0001] The present invention relates to novel peroxide curable fluoroelastomer compositions based on fluoroelastomers manufactured without the use of fluorinated surfactants, and a process for producing fluoroelastomer mouldings using these compositions. BACKGROUND

[0002] This application claims priority from European Patent Application 23164295.0 filed on 27 March 2023, the entire contents of which are incorporated herein by reference for all purposes.

[0003] Fluoroelastomers based on vinylidene fluoride (also known as 1,1-difluoroethylene or VDF) are a class of high performance materials that have a wide range of applications, encompassing O-rings, valve stem seals, shaft seals, gaskets and hoses in the chemical processing industry (CPI).

[0004] Typically, VDF-based fluoroelastomers are amorphous copolymers of VDF produced via an emulsion polymerisation process by reacting a water-soluble polymerisation initiator in the presence of fluorinated monomers and usually one or more surfactants (also known as emulsifiers). In the past, fluorinated surfactants have been used as emulsifiers, however, in order to improve the environmental impact of the process, emulsion polymerisation processes using non-fluorinated surfactants have been developed. In recent years, a process for manufacturing VDF-based fluoroelastomers via emulsion polymerisation without the use of any surfactants has also been described in, for example, WO2019 / 002180.

[0005] The resulting fluoroelastomer is typically moulded in the shape of the desired object and then cured (the process is also known as “vulcanisation”) in order to produce the final cured part.

[0006] It should be appreciated that the properties of the final cured part made from such fluoroelastomers are greatly influenced by the curing system employed, with peroxide-based curing being considered to offer higher performance than bisphenol-based ionic curing.

[0007] In peroxide-based curing, a peroxide is added to the fluoroelastomer, which contains certain curative sites capable of reacting under free radical conditions as pendant groups in the repeating units of the main chain or as end groups, and to a multifunctional unsaturated compound. Upon the action of heat, the peroxide generates free radicals which promote the reaction of the fluoroelastomer chains activated through the curative sites with the multifunctional unsaturated compound to produce a cured mass with chemically interconnected polymer chains.

[0008] It has been observed that in some cases, the cure efficiency of VDF-based fluoroelastomers produced without the use of fluorinated surfactants is lower compared to the cure of fluoroelastomers produced with traditional methods using fluorinated surfactants of the same composition in terms of monomers and cure sites. As detailed in the experimental section of the present document, it has been particularly observed that certain VDF-based fluoroelastomers having iodine / bromine cure sites and which have been subjected to peroxide-based cure have poor compression set (c-set) values when obtained from emulsion processes performed in the absence of fluorosurfactants.

[0009] It is not clear why this effect is observed, without being bound by theory, we speculate that this effect can be due to a different distribution and type of chain end groups in fluoroelastomers obtained from processes that do not employ fluorinated surfactants.

[0010] Therefore, there is a need to improve the cure performance of fluoroelastomer compositions wherein the fluoroelastomer is produced via emulsion polymerization without the use of fluorinated surfactants.

[0011] Therefore, it is an object of the present invention to provide a fluoroelastomer composition wherein the fluoroelastomer is obtained from an emulsion polymerization process without the use of fluorinated surfactants, which after peroxide-based cure has comparable performance in terms of c-set values to similar compositions wherein the fluoroelastomer is obtained from traditional emulsion processes using fluorinated surfactants. SUMMARY

[0012] The present invention relates to a fluoroelastomer composition comprising:

[0013] (i) a fluoroelastomer (fluoroelastomer A), said fluoroelastomer A:

[0014] - obtained from an emulsion polymerization process performed in the absence of fluorinated surfactants,

[0015] - comprising iodine and / or bromine atoms, and

[0016] - having a backbone comprising 40-80% by moles of repeating units derived from vinylidene fluoride (VDF), 20-60% by moles of repeating units derived from one or more additional fluorinated monomers different from VDF,

[0017] (ii) one or more organic peroxides

[0018] (iii) one or more cure co-agents

[0019] (iv) one or more fatty acid salts.

[0020] The Applicant has surprisingly found that the addition of a fatty acid salt to the composition improves the c-set properties of the material after curing, so that a composition containing a fluoroelastomer manufactured in the absence of fluorinated surfactants has substantially the same c-set properties as a composition containing a fluoroelastomer manufactured using fluorinated surfactants. DETAILED DESCRIPTION

[0021] For the purposes of the present description and of the following claims:

[0022] - the use of round brackets around an identifying symbol or number, for example in expressions like "fluoroelastomer (A)", etc., has the sole purpose of better distinguishing the symbol or number from the rest of the text, and therefore said round brackets can also be omitted;

[0023] - the expressions "fluorinated surfactant", "fluorinated monomer", etc. are intended to encompass both partially and totally fluorinated compounds, unless otherwise specified.

[0024] - the term "phr" as commonly used in the elastomer industry means "parts per hundred rubber", i.e. parts by weight per 100 parts by weight of elastomer.

[0025] - the term "fluoroelastomer" indicates a polymer used as a base ingredient for obtaining a true elastomer. Such polymers are amorphous polymers or polymers having a low crystallinity (having a heat of fusion of less than 5 J / g, preferably less than 3 J / g, more preferably less than 1 J / g, as measured by ASTM D-3418) and a glass transition temperature (T g ) lower than room temperature. In most cases, the fluoroelastomer (A) advantageously has a T g .

[0026] A true elastomer is defined by the ASTM, Special Technical Bulletin, No. 184 standard, as a material that is able to be stretched at room temperature to twice its original length and, after 5 minutes under tension, will return to no more than 10% from its original length in the same time once it is released.

[0027] The composition of the present application comprises a fluoroelastomer A comprising from 40% to 80% by moles of repeating units derived from vinylidene fluoride (VDF) and from 20% to 60% by moles of repeating units derived from one or more additional fluorinated monomers different from VDF. Optionally, the fluoroelastomer A can further comprise repeating units derived from one or more ethylenically unsaturated monomers not containing fluorine atoms (hereinafter, hydrogenated monomers).

[0028] Non-limiting examples of suitable fluorinated monomers, different from VDF, that can be used in the fluoroelastomer A of the present application are notably:

[0029] (a) C2-C8 perfluoroolefins, such as tetrafluoroethylene (TFE), hexafluoropropylene (HFP);

[0030] (b) C2-C8 olefins containing hydrogen, such as vinyl fluoride (VF), trifluoroethylene (TrFE), hexafluoroisobutene (HFIB), perfluoroalkyl ethylenes having the formula CH2=CH-R f , wherein R f is a C1-C6 perfluoroalkyl group;

[0031] (c) C2-C8 fluoroolefins comprising at least one of iodine, chlorine and bromine, such as chlorotrifluoroethylene (CTFE);

[0032] (d) (per)fluoroalkyl vinyl ethers (PAVE) having the formula CF2=CFOR f , wherein R f is a C1-C6 (per)fluoroalkyl group, preferably CF3, C2F5, C3F7;

[0033] (e) (per)fluoro-oxy-alkyl vinyl ethers having the formula CF2=CFOX, wherein X is a C1-C 12 ((per)fluoro)-oxyalkyl group comprising a chain of oxygen atoms, for example perfluoro-2-propyloxypropyl;

[0034] (f) (per)fluorodioxoles having the formula:

[0035]

[0036] wherein R f3 , R f4 , R f5 , R f6 are each equal to or different from each other, independently selected from the group consisting of a fluorine atom and a C1-C6 (per)fluoroalkyl group optionally comprising one or more than one oxygen atom, notably such as -CF3, -C2F5, -C3F7, -OCF3, -OCF2CF2OCF3; preferably, perfluorodioxoles;

[0037] (g) (per)fluoro-methoxy-vinyl ethers (MOVE, hereinafter) having the formula:

[0038] CF2=CFOCF2OR f2

[0039] wherein R f2R is selected from the group consisting of C1-C6 (per)fluoroalkyl; C5-C6 cyclic (per)fluoroalkyl; and C2-C6 (per)fluorooxyalkyl comprising at least one catenary oxygen atom; R f2 is -CF2CF3 (MOVE1); -CF2CF2OCF3 (MOVE2); or -CF3 (MOVE3).

[0040] Examples of optional hydrocarbon monomers are C2-C8 non-fluorinated olefins (Ol), such as ethylene, propylene, 1-butene, diene monomers, styrene monomers. Such optional hydrocarbon monomers, if present, preferably constitute less than 20% by moles, preferably less than 10% by moles, more preferably less than 5% by moles, based on the total repeating units of fluoroelastomer A.

[0041] Optionally, fluoroelastomer (A) further comprises repeating units derived from one or more di-olefins [di-olefins (OF)] having the general formula:

[0042]

[0043] wherein R1, R2, R3, R4, R5 and R6 are, the same or different from each other, H or C1-C5 alkyl; Z is a linear or branched, optionally containing oxygen atoms, preferably at least partially fluorinated C1-C 18 hydrocarbyl (including alkylene or cycloalkylene), or (per)fluoropolyoxyalkylene, for example as described in EP 661304 A (AUSIMONT SPA) 5 / 07 / 1995.

[0044] The one or more di-olefins (OF), if present, are preferably selected from the group consisting of di-olefins complying with formulae (OF-1), (OF-2) and (OF-3):

[0045] (OF-1)

[0046]

[0047] wherein j is an integer between 2 and 10, preferably between 4 and 8, and R1, R2, R3, R4 are, the same or different from each other, H, F or C 1-5 alkyl or (per)fluoroalkyl;

[0048] (OF-2)

[0049]

[0050] wherein each A is, the same or different from each other and at each occurrence, independently selected from F, Cl and H; each B is, the same or different from each other and at each occurrence, independently selected from F, Cl, H and ORB wherein R B is a branched or linear alkyl group which can be partially, substantially or completely fluorinated or chlorinated; E is a divalent group having 2 to 10 carbon atoms which can be optionally fluorinated, which can be inserted with ether linkages; preferably, E is a -(CF2) m group, wherein m is an integer from 3 to 5; a preferred di-olefin of the (OF-2) type is F2C=CF-O-(CF2)5-O-CF=CF2.

[0051] (OF-3)

[0052]

[0053] wherein E, A and B have the same meaning as defined above; R5, R6, R7, equal to or different from each other, are H, F or C 1-5 alkyl or (per)fluoroalkyl.

[0054] When one or more di-olefins are employed, the resulting fluoroelastomer A typically comprises from 0.01 to 5% by moles relative to the total amount of units of said fluoroelastomer A of units derived from the one or more di-olefins.

[0055] Exemplary fluoroelastomers (A) which can be used in the composition of the present application are those having the following monomer composition (in mol% relative to the total moles of repeating units):

[0056] (i) vinylidene fluoride (VDF) 40-80%, hexafluoropropene (HFP) 10-45%, tetrafluoroethylene (TFE) 0-30%, (per)fluoroalkyl vinyl ether (PAVE) 0-15%; di-olefin (OF): 0-5%;

[0057] (ii) vinylidene fluoride (VDF) 50-80%, (per)fluoroalkyl vinyl ether (PAVE) 5-50%, tetrafluoroethylene (TFE) 0-20%, di-olefin (OF): 0-5%;

[0058] (viii) vinylidene fluoride (VDF) 40-85%, (per)fluoro-methoxy-vinyl ether (MOVE) 5-40%, (per)fluoroalkyl vinyl ether (PAVE) 0-30%, tetrafluoroethylene (TFE) 0-40%, hexafluoropropene (HFP) 0-30%; di-olefin (OF): 0-5%.

[0059] The fluoroelastomer (A) comprises iodine and / or bromine atoms; the choice among iodine / bromine is not particularly critical, provided that they ensure sufficient reactivity in the curing. However, iodine is generally preferred.

[0060] These iodine or bromine atoms can be included in the fluoroelastomer (A) as pendant groups bound to the main chain of the polymer chain of the fluoroelastomer (A) (by introducing in the fluoroelastomer (A) chain repeat units derived from monomers having iodine and / or bromine atoms, referred to as cure site containing repeat units) and / or can be included as end groups of said polymer chain.

[0061] Among the cure site containing repeat units, one can notably mention:

[0062] (CSM-1) iodine or bromine containing monomer of formula:

[0063]

[0064] where each A Hf are identical to or different from each other and at each occurrence, independently selected from F, CI and H; B Hf is F, CI, H and OR Hf B, where R Hf B is a branched or linear alkyl group which can be partially, substantially or completely fluorinated or chlorinated; each W Hf are identical to or different from each other and at each occurrence, independently are a covalent bond or an oxygen atom; E Hf is a divalent group having from 2 to 10 carbon atoms which can be optionally fluorinated; R Hf is a branched or linear alkyl group which can be partially, substantially or completely fluorinated; and R Hf is a halogen atom selected from the group consisting of iodine and bromine; which can be inserted with an ether linkage; preferably E is a -(CF2) m group, where m is an integer from 3 to 5;

[0065] (CSM-2) possibly fluorinated cyano containing ethylenically unsaturated compound.

[0066] Among the cure site containing monomers of type (CSM1), preferred monomers are those selected from the group consisting of:

[0067] (CSM1-A) iodine containing perfluorovinyl ether of formula:

[0068]

[0069] wherein m is an integer from 0 to 5 and n is an integer from 0 to 3, with the proviso that at least one of m and n is different from 0, and Rfi is F or CF3; (as described especially in patents US 4745165 (OCSILMONT CORP.), US 4564662 (MINNESOTA MINING) and EP 199138 A (DAIKIN IND., LTD.)); and

[0070] (CSM-1 B) iodine-containing ethylenically unsaturated compounds having the formula:

[0071] CX1X2= CX3- (CF2CF2) p -I

[0072] wherein each of X1, X2and X3, equal to or different from each other, is independently H or F; and p is an integer from 1 to 5; among these compounds, mention can be made of CH2=CHCF2CF2I, I(CF2CF2)2CH=CH2, ICF2CF2CF=CH2, I(CF2CF2)2CF=CH2;

[0073] (CSM-1 C) iodine-containing ethylenically unsaturated compounds having the formula:

[0074] CHR=CH-Z-CH2CHR-I

[0075] wherein R is H or CH3, Z is a C1-C18 (per)fluoroalkylene, linear or branched, optionally containing one or more ether oxygen atoms, or a (per)fluoropolyoxyalkylene; among these compounds, mention can be made of CH2=CH-(CF2)4CH2CH2I, CH2=CH-(CF2)6CH2CH2I, CH2=CH-(CF2)8CH2CH2I, CH2=CH-(CF2)2CH2CH2I;

[0076] (CSM-1 D) bromo- and / or iodo alpha-olefins containing from 2 to 10 carbon atoms, such as, for example, bromotrifluoroethylene or bromotetrafluorobutene as described in US 4035565 (DU PONT), or other compounds bromo- and / or iodo alpha-olefins disclosed in US 4694045 (DU PONT).

[0077] According to a first embodiment, iodine and / or bromine atoms are included as pendant groups bound to the main chain of the fluorocopolymer chain. The fluorocopolymer according to this embodiment generally comprises, per 100 mol of all other repeating units of the fluorocopolymer (A), an amount of 0.05 to 5 mol of repeating units derived from iodine- or bromine-containing monomers (CSM-1) so as to advantageously ensure a weight content of iodine and / or bromine to meet the requirements for achieving a sufficient curing rate and crosslinking density.

[0078] According to a second preferred embodiment, iodine and / or bromine atoms are included as end groups of the fluorocopolymer (A); the perfluorocopolymer according to this embodiment is generally obtained by adding to the polymerization medium during fluorocopolymer manufacture any one of:

[0079] - one or more iodinated and / or brominated chain transfer agents; suitable chain- chain transfer agents are typically those having formula R f (I) x (Br) y wherein R f is a (per)fluoroalkyl or (per)fluorochloroalkyl group containing from 1 to 8 carbon atoms, while x and y are integers between 0 and 2, with 1 < x + y < 2 (see for example patents US 4243770 (DAIKIN INDUSTRIES CO., LTD.) 6 / 01 / 1981 and US 4943622 (NIPPON MEKTRON KK) 24 / 07 / 1990); and

[0080] - alkali or alkaline-earth metal iodides and / or bromides, as notably described in patent US 5173553 (AUSIMONT SRL) 22 / 12 / 1992.

[0081] That is, the preferred reagent (CTA-X) is an iodinated and / or brominated organic chain transfer agent, more preferably those having formula R f (I) x (Br) y wherein R f is a (per)fluoroalkyl or (per)fluorochloroalkyl group containing from 1 to 8 carbon atoms, while x and y are integers between 0 and 2, with 1 < x + y < 2; and most preferably those having formula R' f (I) x ’(Br) y ’ wherein R' f is a perfluoroalkyl group containing from 1 to 8 carbon atoms, while x' and y' are integers between 0 and 2, with 1 < x' + y' < 2, most preferably x' = 2 and y' = 0.

[0082] In the process of the application, the reagent (CTA-X) that is preferably iodinated, in particular of formula R f (I)2or R’ f (I)2, wherein R f and R’ f As detailed above.

[0083] When a chain transfer agent is used, the amount typically used is 1 to 100 mmol of I and / or Br per kg of fluoroelastomer.

[0084] The fluoroelastomer (A) of the application advantageously comprises iodine and / or bromine atoms in an amount of 0.001 to 10% wt., preferably 0.05 to 5% wt., more preferably 0.1 to 2% wt., even more preferably 0.1 to 1% wt., relative to the total weight of the fluoroelastomer (A).

[0085] As mentioned above, the fluoroelastomer A of the application is obtained from an emulsion polymerization process carried out in the absence of fluorinated surfactants. Preferably in the absence of surfactants including fluorinated and non-fluorinated surfactants.

[0086] The process for the preparation of the fluoroelastomer A typically comprises a step wherein an aqueous reaction medium is formed within a sealable reactor, the reaction medium being free of fluorinated surfactants and comprising a free radical initiator, optionally a chain transfer agent, preferably an iodine-containing chain transfer agent. Typically the reactor is sealed and pressurized with a monomer gas comprising VDF, while other monomers are added as a gas or a liquid according to the type of monomers. Typically, the polymerization is carried out at a temperature of 40°C to 120°C, more preferably 50°C to 100°C and at a pressure of between 10 and 60 bars, more preferably 20 to 55 bars.

[0087] While the choice of the free radical initiator is not particularly limited, it is understood that those free radical initiators suitable for use in the process according to the application are selected from compounds capable of initiating and / or accelerating the polymerization process.

[0088] Inorganic free radical initiators can be used and these include, but are not limited to, persulfates such as sodium persulfate, potassium persulfate and ammonium persulfate, permanganates such as potassium permanganate.

[0089] Additionally, organic free radical initiators can be used and these include, but are not limited to, the following: acetyl cyclohexane sulfonyl peroxide; diacetyl peroxide dicarbonate; dialkyl peroxides such as diethyl peroxide, dicyclohexyl peroxide, di-2-ethylhexyl peroxide; tert-butyl peroxynonanoate; 2,2'-azobis(4-methoxy-2,4 dimethyl valeronitrile; tert-butyl peroxypivalate; dioctanoyl peroxide; dilauroyl peroxide; 2,2'-azobis(2,4-dimethyl valeronitrile); tert-butyl azo-2-cyanobutane; dibenzoyl peroxide; tert-butyl-per-2-ethylhexanoate; tert-butyl peroxymaleate; 2,2'-azobis(isobutyronitrile); bis(tert-butylperoxy)cyclohexane; tert-butylperoxy isopropyl carbonate; tert-butyl peracetate; 2,2'-bis(tert-butylperoxy)butane; dicumyl peroxide; di-tert-amyl peroxide; di-tert-butyl peroxide (DTBP); p-methane hydroperoxide; pinane hydroperoxide; cumene hydroperoxide; and tert-butyl hydroperoxide.

[0090] Other suitable free radical initiators include, among others, halogenated free radical initiators such as chloroalkane-based and fluoroalkane-based acyl peroxides such as trichloroacetyl peroxide, bis(perfluoro-2-propyloxypropionyl) peroxide, [CF3CF2CF2OCF(CF3)COO]2, perfluoropropionyl peroxide, (CF3CF2CF2COO)2, (CF3CF2COO)2, {(CF3CF2CF2)-[CF(CF3)CF2O] m -CF(CF3)-COO}2(where m = 0-8), [ClCF2(CF2) n COO]2, and [HCF2(CF2) n COO]2(where n = 0-8); perfluoroalkyl azo compounds such as perfluoroazoisopropane, [(CF3)2CFN=]2, RN=NR¤ (where R¤ is a linear or branched perfluorocarbon group having 1-8 carbons); stable or hindered perfluoroalkyl radicals such as hexafluoropropylene trimer radical, [(CF3)2CF]2(CF2CF2)C• radical, and perfluoroalkanes.

[0091] Redox systems comprising at least two components forming a redox pair such as dimethylaniline-benzoyl peroxide, diethylaniline-benzoyl peroxide, and diphenylamine-benzoyl peroxide can also be used as free radical initiators to initiate the polymerization process.

[0092] A particularly suitable process for the preparation of fluoroelastomer A via emulsion polymerization without the use of surfactants and in particular without the use of fluorinated surfactants is the process described in WO 2019 / 002180 (Solvay Specialty Polymers Italy S.p.A.), wherein the polymerization process is carried out in the presence of a redox initiation system comprising at least one organic free-radical initiator and at least one compound bearing at least one sulfinic acid group.

[0093] Examples of fluorinated surfactants not used in the present invention are fluorinated surfactants complying with the following formula:

[0094] R * -X B- (T + )

[0095] wherein

[0096] R * is a C5-C16 (per)fluoroalkyl chain or a (per)fluoropolyoxyalkylene chain comprising one or more ether oxygen,

[0097] X B- is -COO - or -SO3 - ,

[0098] T + is selected from the group consisting of: H + , NH4 + , and an alkali metal ion.

[0099] In particular, the fluorinated surfactants not used herein are those corresponding to the following general formula:

[0100]

[0101] wherein X1, X2, X3, equal to or different from each other, are independently selected from the group consisting of H, F, and C1-6 (per)fluoroalkyl optionally comprising one or more catenary or non catenary oxygen atoms; L represents a bond or a divalent group; RF is a divalent fluorinated C1-3 bridging group; Y is a hydrophilic functional group selected from the group consisting of anionic, cationic and non-ionic functional groups.

[0102] Exemplary embodiments of fluorinated surfactants not added in the process of the present invention are, among others: ammonium perfluorooctanoate; (per)fluoropolyoxyalkylenes terminated with one or more carboxyl groups, which can optionally be salified with sodium, ammonium and alkali metals; and partially fluorinated alkyl sulfonates and compounds having the following formula:

[0103]

[0104] wherein Xa is an alkali metal or ammonium moiety.

[0105] The composition of the application comprises one or more organic peroxides (O) and one or more curing co-agents (U) which together form a crosslinking system capable of promoting the curing of the fluoroelastomer A.

[0106] The choice of the one or more organic peroxides (O) is not particularly critical, provided that the one or more organic peroxides are capable of generating free radicals with the help of the transition metal catalyst. Among the most commonly used peroxides, mention can be made of:

[0107] - di(alkyl / aryl)peroxides, including for example di-tert-butyl peroxide, 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane, di(tert-butylperoxy isopropyl)benzene, dicumyl peroxide;

[0108] - diacyl peroxides, including dibenzoyl peroxide, disuccinyl peroxide, di(4-methylbenzoyl) peroxide, di(2,4-dichlorobenzoyl) peroxide, dilauroyl peroxide, decanoyl peroxide;

[0109] - percarboxylic acids and esters, including di-tert-butyl perbenzoate, tert-butyl peroxy-2-ethylhexanoate, 1,1,3,3-tetramethylethylbutyl peroxy-2-ethylhexanoate, 2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)hexane;

[0110] - peroxy carbonates, including notably di(4-tert-butylcyclohexyl) peroxydicarbonate, di(2-phenoxyethyl) peroxydicarbonate, bis[1,3-dimethyl-3-(tert-butylperoxy)butyl]carbonate, tert-hexyl peroxyisopropyl carbonate, tert-butyl peroxyisopropyl carbonate;

[0111] - perketals, such as 1,1 -bis(tert-butylperoxy)cyclohexane and 2,2-bis(tert- butylperoxy)butane;

[0112] - ketone peroxides, such as cyclohexanone peroxide and acetylacetone peroxide;

[0113] - organic hydroperoxides, such as cumene hydroperoxide, tert-butyl hydroperoxide, methyl ethyl ketone peroxide (otherwise known as 2-[(2-hydroperoxybutane-2-yl)peroxy]butane-2-peroxol) and pinane hydroperoxide;

[0114] - 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'-azobisdimethyl isobutyrate, dimethyl-2,2'-azobis(2-methylpropanate), 2,2'-azobis(2-methylbutyronitrile), 1,1 '-azobis(cyclohexane-1 - carbonitrile), 2,2'-azobis[N-(2-propenyl)-2-methylpropionamide], 1 -[(1 -cyano-1 - methylethyl)azo]formamide, 2,2'-azobis(N-cyclohexyl-2-methylpropionamide), 2,2'-azobis(isobutyronitrile), 2,2'-azobis(2-cyano-2-butane), dimethyl-2,2'-azobisdimethyl isobutyrate, 1,1 '-azobis(cyclohexanecarbonitrile), 2-(tert-butylazo)-2-cyanopropane, 2,2'-azobis[2-methyl-N-(1,1)-bis(hydroxymethyl)-2- hydroxyethyl]propionamide, 2,2'-azobis[2-methyl-N-hydroxyethyl]-propionamide, 2,2'-azobis(N,N'-dimethyleneisobutylamide), 2,2'-azobis(2-methyl-N-[1,1 -bis(hydroxymethyl)-2- hydroxyethyl]propionamide), 2,2'-azobis(2-methyl-N-[1,1 -bis(hydroxymethyl)ethyl])propionamide, 2,2'-azobis[2-5methyl-N-(2-hydroxyethyl)propionamide], 2,2'-azobis(isobutyramide) dihydrate, 2,2'-azobis(2,2,4-trimethylpentane), 2,2'-azobis(2-methylpropane).

[0115] Other suitable peroxide systems are those described notably in patent applications EP 136596 A (MONTEDISON SPA) 10 / 04 / 1985 and EP 410351 A (OSISUM LTD) 30 / 01 / 1991, the contents of which are incorporated herein by reference.

[0116] The person of ordinary skill in the art will make the most appropriate selection of peroxide depending on the curing conditions (time, temperature).

[0117] The amount of peroxide (O) in the composition of this example is generally 0.1 to 15 phr, preferably 0.2 to 12 phr, more preferably 1.0 to 7.0 phr (as is common in the art, “phr” is intended as “parts of peroxide by weight relative to 100 parts by weight of fluoroelastomer A”).

[0118] The one or more curing co-agents U are selected from polyunsaturated compounds. The expression "polyunsaturated compounds" is intended here to indicate compounds comprising more than one carbon-carbon unsaturation.

[0119] The compounds (U) can 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.

[0120] Among the compounds (U) comprising two carbon-carbon unsaturations, mention can be made of the bis-olefins [bis-olefins (OF)] as detailed above, preferably selected from those complying with any one of the formulae (OF-1), (OF-2) and (OF-3) as detailed above.

[0121] Among the compounds (U) comprising three carbon-carbon unsaturations, mention can be made of:

[0122] (i) - tri-substituted cyanurate compounds of the following general formula:

[0123]

[0124] wherein each R cy are identical to or different from each other and at each occurrence, are independently selected from H or a group -R rcy or -OR rcy wherein R rcy is a C1-C5 alkyl, possibly comprising one or more halogens, and each J cy are identical to or different from each other and at each occurrence, are independently selected from a bond or a divalent hydrocarbon group optionally comprising heteroatoms;

[0125] Among this group, preferred compounds are triallyl cyanurate and tri-vinyl cyanurate;

[0126] (ii) - tri-substituted isocyanurate compounds of the following general formula:

[0127]

[0128] wherein each R isocy are identical to or different from each other and at each occurrence, are independently selected from H or a group -R risocy or -OR risocy wherein R risocy is a C1-C5 alkyl, possibly comprising one or more halogens, and each J isocy are identical to or different from each other and at each occurrence, are independently selected from a bond or a divalent hydrocarbon group optionally comprising heteroatoms;

[0129] Among this group, the preferred compounds are triallyl isocyanurate (also known as "TAIC"), triallyl isocyanurate, among which TAIC is the most preferred;

[0130] (iii) - tri-substituted triazine compounds having the following general formula:

[0131]

[0132] wherein each R az are, the same as or different from each other and at each occurrence, independently selected from H or a group -R raz or -OR raz wherein R raz is a C1-C5 alkyl, possibly containing one or more halogens, and each J az are, the same as or different from each other and at each occurrence, independently selected from a bond or a divalent hydrocarbon group optionally containing heteroatoms;

[0133] Tri-substituted triazine compounds include, among others, the compounds disclosed in EP 0860436 A (Ossiamont S.A.) 26 / 08 / 1998 and WO 97 / 05122 (DuPont) 13 / 02 / 1997;

[0134] (iv) - tri-substituted phosphite compounds having the following general formula:

[0135]

[0136] wherein each R ph are, the same as or different from each other and at each occurrence, independently selected from H or a group -R rph or -OR rph wherein R rph is a C1-C5 alkyl, possibly containing one or more halogens, and each J ph are, the same as or different from each other and at each occurrence, independently selected from a bond or a divalent hydrocarbon group optionally containing heteroatoms;

[0137] The preferred compounds of this group include triallyl phosphite;

[0138] (v) - tri-substituted alkyltrisiloxanes having the following general formula:

[0139]

[0140] wherein each R si are, the same as or different from each other and at each occurrence, independently selected from H or a group -R rsi or -OR rsi wherein R rsiC1-C5 alkyl, possibly comprising one or more halogens, and each R' si each J, equal to or different from each other and at each occurrence, is independently selected from the group consisting of a bond or a divalent hydrocarbon group optionally comprising heteroatoms; si each J, equal to or different from each other and at each occurrence, is independently selected from the group consisting of a bond or a divalent hydrocarbon group optionally comprising heteroatoms;

[0141] Preferred compounds of this group include 2,4,6-trivinylmethyltrisiloxane and 2,4,6-trivinylethyltrisiloxane;

[0142] (vi) N,N-disubstituted acrylamide compounds having the general formula:

[0143]

[0144] wherein each R an each J, equal to or different from each other and at each occurrence, is independently selected from the group consisting of a bond or a divalent hydrocarbon group optionally comprising heteroatoms; ran or -OR ran wherein R ran C1-C5 alkyl, possibly comprising one or more halogens, and each J an each J, equal to or different from each other and at each occurrence, is independently selected from the group consisting of a bond or a divalent hydrocarbon group optionally comprising heteroatoms;

[0145] Preferred compounds of this group include N,N-diallylacrylamide.

[0146] Among the compounds (U) comprising four or more carbon-carbon unsaturations, mention can be made of tris(diallylamine)-s-triazine having the following formula:

[0147]

[0148] hexa-allylphosphoramide, N,N,N',N'-tetra-allylterephthalamide, N,N,N',N'-tetra-allylmalonamide.

[0149] For compound (U), it is generally preferred to select from the group consisting of di-olefins (OF) as detailed above, in particular olefins of the (OF-1) type, and tri-substituted isocyanurate compounds as detailed above, in particular TAIC.

[0150] The amount of compound (U) typically ranges from 0.1 to 20 phr, preferably from 1 to 15 phr, more preferably from 1 to 10 phr (as common in the art, “phr” is intended as “parts of polyunsaturated compound U by weight with respect to 100 parts by weight of fluoroelastomer A”).

[0151] Another component of the composition of the present application is one or more fatty acid salts.

[0152] Preferably, the one or more fatty acid salts are selected from metal salts of fatty acids. The metal of the metal salt of fatty acid is for example an alkali metal, an alkaline earth metal, a transition metal. Preferred metals are sodium, potassium, calcium, magnesium, barium, zinc, aluminum. Suitable carbon chain of the fatty acid salt is preferably C12-28, more preferably C14-C26, even more preferably C16-C24, most preferably C16-C22.

[0153] The metal salt of fatty acid can be for example a salt of behenic acid (C22), eicosanoic acid (C20), stearic acid (C18), palmitic acid (C16), myristic acid (C14) or lauric acid (C12). Among them, salts of stearic acid and palmitic acid are preferred, metal salts of stearic acid are more preferred.

[0154] The most preferred metal salt of fatty acid for use herein is sodium stearate, potassium stearate, barium stearate, calcium stearate, zinc stearate, magnesium stearate or aluminum stearate.

[0155] The amount of fatty acid salt that can be used in the composition of the present application is typically 0.05 to 5 phr, preferably 0.1 to 2 phr, more preferably 0.1 to 1.5 phr, most preferably 0.2 to 1 phr.

[0156] The composition of the present application can further additionally comprise ingredients that can be typically used for peroxide cure of fluoroelastomers; more specifically, the composition can typically further comprise

[0157] (a) one or more than one metal basic compound, typically in an amount of 0.5 to 15.0 phr, and preferably 1 to 10 phr, more preferably 1 to 5 phr, relative to 100 parts by weight of fluoroelastomer (A); the metal basic compound is typically selected from the group consisting of (j) oxides or hydroxides of divalent metals, such as Mg, Zn, Ca or Pb, and (jj) metal salts of weak acids, such as stearates, benzoates, carbonates, oxalates or phosphites of Ba, Na, K, Pb, Ca;

[0158] (b) one or more than one acid acceptor that is not a metal basic compound, typically in an amount of 0.5 to 15.0 phr, and preferably 1 to 10.0 phr, more preferably 1 to 5 phr, relative to 100 parts by weight of fluoroelastomer (A); these acid acceptors are typically selected from nitrogen-containing organic compounds, such as 1,8-bis(dimethylamino)naphthalene, octadecylamine and the like, as notably described in EP 708797 A (DuPont) 1 / 05 / 1996.

[0159] Generally, the presence of metal basic oxides is not preferred as it has been found to reduce the chemical resistance, in particular with respect to acid resistance, of the cured fluoroelastomer parts under certain conditions.

[0160] The composition of the application can comprise other conventional additives such as fillers, thickeners, pigments, antioxidants, stabilizers, processing aids / plasticizers, etc. Carbon black is often used as an advantageous reinforcing system.

[0161] In another aspect, the application relates to a process for manufacturing a composition as described above, the process comprising manufacturing said fluoroelastomer A comprising iodine and / or bromine atoms and having a backbone comprising 40-80% by moles of repeating units derived from vinylidene fluoride (VDF), 20-60% by moles of repeating units derived from one or more additional fluorinated monomers different from VDF, using an emulsion polymerization process carried out in the absence of fluorinated surfactants.

[0162] The process further comprises mixing said fluoroelastomer A with one or more organic peroxides, one or more curing co-agents, and one or more fatty acid salts.

[0163] In another aspect, the application relates to a process for manufacturing a shaped article, the process comprising curing a composition of the application as described above.

[0164] The composition can be manufactured into a desired shaped article, for example, by molding (injection molding, extrusion molding), calendering, coating, screen printing, in situ forming, advantageously subjecting the shaped article to vulcanization (curing) during the process of its own manufacture and / or in a subsequent step (post-treatment or post-curing); advantageously transforming the relatively soft, weak, fluoroelastomeric uncured composition into a finished product made of a non-sticky, strong, insoluble, chemically and heat resistant cured fluoroelastomeric material.

[0165] The application also relates to cured articles obtained from the composition as detailed above. Said cured articles are generally obtained by molding and curing the fluoroelastomer composition as detailed above. These cured articles can be sealing articles, including O (square)-rings, gaskets, pads, diaphragms, shaft seals, valve stem seals, piston rings, crankshaft seals, camshaft seals, and oil seals, or possibly pipes and tubes, in particular flexible hoses or other items, including conduits for delivering hydrocarbon fluids and fuels.

[0166] The application further relates to an assembly comprising a substrate and at least one cured article as detailed above.

[0167] The choice of the substrate is not particularly limited: the compositions of the present application are such as to ensure adhesion to various metallic and non-metallic substrates, notably including plastic and rubber substrates, among which mention can be made notably of polyamide substrates, silicone substrates.

[0168] The assembly of the present application is generally manufactured by contacting the composition (C) as above detailed with the substrate; and subjecting the composition (C) to vulcanization (curing) while in contact with the substrate; and optionally exposing the assembly to a subsequent heat treatment step (post-treatment or post-curing).

[0169] The Applicant has surprisingly found that the cured article obtained from the composition of the present application has a reduced c-set value (which reflects a more efficient and improved curing process) if compared to the cured article obtained from the same composition wherein the fatty acid salt is not comprised.

[0170] Therefore, another aspect of the present application is the use of a fatty acid salt for reducing the c-set value of a cured material obtained from a cured composition comprising:

[0171] (i) a fluoroelastomer (fluoroelastomer A), said fluoroelastomer A:

[0172] - is obtained from an emulsion polymerization process carried out in the absence of fluorinated surfactants,

[0173] - comprises iodine and / or bromine atoms, and

[0174] - has a main chain comprising from 40% to 80% by moles of repeating units derived from vinylidene fluoride (VDF), from 20% to 60% by moles of repeating units derived from one or more additional fluorinated monomers different from VDF,

[0175] (ii) one or more organic peroxides,

[0176] (iii) one or more curing co-agents.

[0177] To the extent the disclosure of any patent, patent application, and publication incorporated herein by reference conflicts with the description of the present application as set forth herein, the description of the present application shall control.

[0178] The present application will now be described in greater detail by reference to the following examples, which are for illustrative purposes only and are not limiting on the scope of the application.

[0179] Example

[0180] Materials used:

[0181] Fluoroelastomer 1- having the following molar composition VDF 70%-HFP 19%-TFE 16% and an iodine content of 0.4% by weight, was prepared as follows:

[0182] After evacuation, a 22 L vertical autoclave, equipped with a stirrer operating at 450 rpm, was fed with 11.5 L of demineralized water. The autoclave was then heated at 80°C and maintained at this temperature for the entire duration of the reaction. The pressure of the autoclave was increased to 13.7 bars by feeding HFP monomer. A gaseous mixture of the following monomers was fed to the autoclave so that the pressure reached 26 bars: VDF 70.5% by moles, HFP 19% by moles, TFE 11% by moles. Then 10.61 g of C4F8I2 and 0.90 g of the bis-olefin of formula

[0183] H2C=CH-(CF2)6-CH=CH2 were introduced. A solution of 8.22 g / l of t-butyl hydroperoxide in demineralized water was pumped into the autoclave at a constant feed rate. Simultaneously, but separately, a solution of 23.5 g / l of Bruggolite type E28 in demineralized water was pumped into the autoclave at a substantially similar feed rate. After initiation, the VDF / HFP / TFE mixture was continuously fed to maintain constant pressure and 16.49 g of bis-olefin was added in 19 steps. After the instantaneous monomer conversion exceeded 2000 g / h, the TBHP and Bruggolite E28 feed rates were reduced by about 25% and kept constant for the remainder of the reaction. At a monomer conversion of 1056 g, 16.3 g of C4F8I2 was added. At a monomer conversion of 4224 g, a final aliquot of 8.98 g of C4F8I2 was introduced.

[0184] The polymerization was continued until a total monomer consumption of 5280 g was reached after 212 minutes; the autoclave was then depressurized, vented and cooled. The latex obtained had a solid content of 26.6% by weight. After coagulation with a solution of AI2(S04)3 and drying, the fluoroelastomer crumbs thus obtained gave a Mooney viscosity (ML) (1+10) at 121 °C of 22, measured.

[0185] Fluoroelastomer 2 - having the same molar composition and iodine content as fluoroelastomer 1, but prepared via emulsion polymerization in the presence of a fluorosurfactant. The same procedure as in fluoroelastomer 1 was followed, but 2.5 g of ammonium persulfate was used as initiator (instead of the E28 / TBHP redox initiator) and 105 ml of a microemulsion was used, which was previously obtained by mixing: 8.8 ml of perfluoropolyoxyalkylene with acidic end groups of formula: n (CF2O)m CF2COOH (where n / m = 10, with a weight average molecular weight of 600), 5.6 ml of a 30% v / v aqueous NH4OH solution, 20.0 ml of demineralized water and 5.5 ml of GALDEN D02 perfluoropolyether having the following formula: CF3O(CF2CF(CF3)O) n (CF2O) m CF3 (where n / m = 20, with an average molecular weight of 450).

[0186] Fluoroelastomer 1-2 obtained from Solvay Specialty Polymers Italy S.p.A.

[0187] Bruggolite E28: obtained from Bruggermann

[0188] Organic Peroxide : 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane from Arkema.

[0189] Curing Aid: triallyl isocyanurate (TAIC) from Degussa.

[0190] Carbon Black N-990: from Cancarb.

[0191] Stearic Acid and all Stearates: obtained from Faci Group.

[0192] Sodium Dodecyl Sulfate: obtained from Sigma Aldrich

[0193] For all examples, the fluoroelastomer was compounded with the additives detailed in the table below in an open mill. The o-rings (size class = 214) were cured in a press mold at 180°C for 10 minutes and then post-processed in an air-circulation oven at 230°C for 4h. The curing process was monitored by moving die rheometer, monitoring the torque curve until plateau was reached at the maximum torque value.

[0194] For each composition, the compression set (c-set) values were determined on cured o-ring test specimens standard AS568A (type 214) according to ASTM D 395 method B (after 70 hours at 200°C).

[0195] The following composition examples 1-6 were prepared as examples according to the present application:

[0196] Example 1:

[0197] Fluoroelastomer 1 : 100 parts by weight,

[0198] Carbon black N-990: 30 parts by weight

[0199] Organic peroxide: 1.35 parts by weight

[0200] Taic: 3 parts by weight

[0201] Calcium stearate: 1 part by weight

[0202] Examples 2-6:

[0203] The same composition as Example 1 except that the following was added instead of calcium stearate:

[0204] Example 2 - Magnesium stearate: 1 part by weight

[0205] Example 3 - Magnesium stearate 0.25 parts by weight

[0206] Example 4 - Zinc stearate 0.25 parts by weight

[0207] Example 5 - Sodium stearate 0.25 parts by weight

[0208] Example 6 - Zinc potassium stearate 0.25 parts by weight.

[0209] The following compositions Comparative Examples 1-3 were prepared as comparative examples:

[0210] Comparative Example 1 :

[0211] The same composition as Example 1 except that no fatty acid salt was added.

[0212] Comparative Example 2 :

[0213] The same composition as Comparative Example 1 except that fluoroelastomer 2 was used instead of fluoroelastomer 1.

[0214] Comparative Example 3:

[0215] The same composition as Example 3 except that fluoroelastomer 2 was used instead of fluoroelastomer 1.

[0216] Comparative Example 4 :

[0217] The same composition as Example 4 except that fluoroelastomer 2 was used instead of fluoroelastomer 1.

[0218] Comparative Example 5 :

[0219] The same composition as Example 5 except that fluoroelastomer 2 was used instead of fluoroelastomer 1.

[0220] Comparative Example 6 :

[0221] The composition of Example 6 was identical except that fluoroelastomer 2 was used in place of fluoroelastomer 1.

[0222] Comparative Example 7 :

[0223] The composition of Example 1 was identical except that the same amount of stearic acid was used in place of calcium stearate.

[0224] Comparative Example 8 :

[0225] The composition of Example 1 was identical except that the same amount of sodium lauryl sulfate was used in place of calcium stearate.

[0226] The resulting c-set values measured on the o-ring samples obtained from the cured compositions as described above are presented in the table below. It can be clearly noted how the c-set value of the composition containing fluoroelastomer 1 (prepared without the use of a fluorinated surfactant) is higher (i.e. less desirable) than the composition containing fluoroelastomer 2 (prepared with the use of a fluorinated surfactant) in the absence of a fatty acid salt. The data show how the addition of any of the tested fatty acid salts (at the tested levels of 1 and 0.25 parts by weight) brings the c-set value of the fluoroelastomer 1 based composition to the same level as obtained from the fluoroelastomer 2 based composition, allowing the use of a more environmentally friendly fluoroelastomer for the same application.

[0227] The data also show that the addition of the same fatty acid salt to the fluoroelastomer 2 based composition has no effect on the c-set value of the o-ring obtained from the composition.

[0228] Comparative Example 6 also shows how the addition of a fatty acid (as an acid, not as a salt) to the fluoroelastomer 1 based composition has no significant effect on the c-set value in place of the fatty acid salt of the present application. Comparative Example 7 shows the effect of using a sodium lauryl sulfate salt in place of the fatty acid salt. This composition could not be cured under conventional curing conditions.

[0229] Table 1

[0230] Fluoroelastomer Additive c-set Example 1 1 Calcium Stearate 1 phr 25 Example 2 1 Magnesium Stearate 1 phr 28 Example 3 1 Magnesium Stearate 0.25 phr 26 Example 4 1 Zinc Stearate 0.25 phr 21 Example 5 1 Sodium Stearate 0.25 phr 24 Example 6 1 Potassium Stearate 0.25 phr 24 Comparative Example 1 1 None 44 Comparative Example 2 2 None 23 Comparative Example 3 2 Magnesium Stearate 0.25 phr 30 Comparative Example 4 2 Zinc Stearate 0.25 phr 24 Comparative Example 5 2 Sodium Stearate 0.25 phr 34 Comparative Example 6 2 Potassium Stearate 0.25 phr 24 Comparative Example 7 1 Stearic Acid 1 phr 39 Comparative Example 8 1 Sodium Dodecyl Sulfate 1 phr No Cure

Claims

1. A fluoroelastomer composition comprising: (i) a fluoroelastomer (fluoroelastomer A), said fluoroelastomer A: - obtained from an emulsion polymerization process carried out in the absence of fluorinated surfactants, - comprising iodine and / or bromine atoms, and - having a backbone comprising 40-80% by moles of repeating units derived from vinylidene fluoride (VDF), 20-60% by moles of repeating units derived from one or more additional fluorinated monomers different from VDF, (ii) one or more organic peroxides, (iii) one or more cure co-agents, (iv) one or more fatty acid salts.

2. The fluoroelastomer composition of claim 1, wherein, The fluoroelastomer comprises iodine and / or bromine atoms in an amount of 0.1 to 10.0% wt with respect to the total weight of fluoroelastomer (A).

3. The fluoroelastomer composition of any preceding claim, wherein, The one or more fatty acid salts are present in an amount of 0.05 to 5 phr.

4. The fluoroelastomer composition of any preceding claim, wherein, The one or more fatty acid salts are selected from metal salts of fatty acids, preferably from those having C12-C28 carbon chain, more preferably C14-C26 carbon chain, even more preferably C16-C24 carbon chain, most preferably C16-C22 carbon chain.

5. The fluoroelastomer composition of any preceding claim, wherein, The one or more organic peroxides are selected from the group consisting of: - di(alkyl / aryl)peroxides, including for example di-tert-butyl peroxide, 2,5-dimethyl-2,5-bis(tert- butylperoxy)hexane, di(tert-butylperoxyisopropyl)benzene, dicumyl peroxide; - diacyl peroxides, including dibenzoyl peroxide, disuccinyl peroxide, di(4-methylbenzoyl) peroxide, di(2,4-dichlorobenzoyl) peroxide, dilauroyl peroxide, decanoyl peroxide; - percarboxylic acids and esters, including di-tert-butyl perbenzoate, tert-butyl peroxy-2-ethylhexanoate, 1,1,3,3-tetramethylethylbutyl peroxy-2-ethylhexanoate, 2,5-dimethyl-2,5-di(2- ethylhexanoylperoxy)hexane; - peroxy carbonates, notably including di(4-tert-butylcyclohexyl) peroxydicarbonate, di(2-phenoxyethyl) peroxydicarbonate, bis[1,3-dimethyl-3-(tert-butylperoxy)butyl]carbonate, tert-hexyl peroxyisopropyl carbonate, tert-butyl peroxyisopropyl carbonate; - perketals, such as 1,1 -bis(tert-butylperoxy)cyclohexane and 2,2-bis(tert-butylperoxy)butane; - ketone peroxides, such as cyclohexanone peroxide and acetylacetone peroxide; - organic hydroperoxides, such as cumene hydroperoxide, tert-butyl hydroperoxide, methyl ethyl ketone peroxide (otherwise known as 2-[(2-hydroperoxybutane-2-yl)peroxy]butane - 2-peroxyalcohol) 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'-azobisdimethyl isobutyrate, dimethyl-2,2'-azobis(2-methylpropionate), 2,2'-azobis(2-methylbutyronitrile), 1,1 '-azobis(cyclohexane-1 - carbonitrile), 2,2'-azobis[N-(2-propenyl)-2-methylpropionamide], 1 -[(1 -cyano-1 - methylethyl)azo]formamide, 2,2'-azobis(N-cyclohexyl-2-methylpropionamide), 2,2'-azobis(isobutyronitrile), 2,2'-azobis(2-cyano-2-butane), dimethyl-2,2'-azobisdimethyl isobutyrate, 1,1 '-azobis(cyclohexanecarbonitrile), 2-(tert-butylazo)-2-cyanopropane, 2,2'-azobis[2-methyl-N-(1,1)-bis(hydroxymethyl)-2- hydroxyethyl]propionamide, 2,2'-azobis[2-methyl-N-hydroxyethyl]-propionamide, 2,2'-azobis(N,N'-dimethyleneisobutylamine), 2,2'-azobis(2-methyl-N-[1,1 -bis(hydroxymethyl)- 2-hydroxyethyl]propionamide), 2,2'-azobis(2-methyl-N-[1,1 -bis(hydroxymethyl)ethyl])propionamide, 2,2'-azobis[2-5methyl-N-(2-hydroxyethyl)propionamide], 2,2'-azobis(isobutyramide) dihydrate, 2,2'-azobis(2,2,4-trimethylpentane), 2,2'-azobis(2-methylpropane).

6. The fluoroelastomer composition of any preceding claim, wherein, The one or more organic peroxides are comprised in an amount of 0.1 to 15 phr, preferably 0.2 to 12 phr, more preferably 1 to 7 phr.

7. The fluoroelastomer composition of any preceding claim, wherein, The one or more additional fluorinated monomers are selected from the group consisting of: (a) C2-C8 perfluoroolefins, such as tetrafluoroethylene (TFE), hexafluoropropylene (HFP); (b) C2-C8 hydrocarbon containing hydrogen, such as vinyl fluoride (VF), trifluoroethylene (TrFE), hexafluoroisobutene (HFIB), perfluoroalkyl ethylenes of the formula CH2=CH-R f where R f is a C1-C6 perfluoroalkyl group; (c) C2-C8 fluoroolefins comprising at least one of iodine, chlorine and bromine, such as chlorotrifluoroethylene (CTFE); (d) (per)fluoroalkyl vinyl ether (PAVE) of the formula CF2=CFOR f wherein R f is a C1-C6 (per)fluoroalkyl group, preferably CF3, C2F5, C3F7; (e) (per)fluoro-oxy-alkyl vinyl ethers of the formula CF2=CFOX, wherein X is a C1-C6 alkyl group comprising a catenary oxygen atom 12 ((per)fluoro)-oxyalkyl, for example perfluoro-2-propyloxypropyl; (f) (per)fluorodioxoles having the following formula: wherein R f3 , R f4 , R f5 , R f6 each, equal to or different from each other, are independently selected from the group consisting of a fluorine atom and a C1-C6 (per)fluoroalkyl group optionally comprising one or more than one oxygen atom, notably such as -CF3, -C2F5, -C3F7, -OCF3, -OCF2CF2OCF3; preferably perfluorodioxole; (g) (per)fluoro-methoxy-vinyl ethers (MOVE, in the following) having the following formula: CF2=CFOCF2OR f2 wherein R f2 is selected from the group consisting of C1-C6 (per)fluoroalkyl; C5-C6 cyclic (per)fluoroalkyl; and C2-C6 (per)fluorooxyalkyl comprising at least one catenary oxygen atom; R f2 is -CF2CF3 (MOVE1); -CF2CF2OCF3 (MOVE2); or -CF3 (MOVE3).

8. The fluoroelastomer composition of any preceding claim, wherein, The one or more curing co-agents are selected from the group consisting of: A: compounds comprising two carbon-carbon unsaturations, preferably selected from bis-olefins having the following general formula: wherein R1, R2, R3, R4, R5and R6are, independently of one another, H or C1-C5alkyl; Z is a linear or branched C1-C6alkylene group, optionally containing oxygen atoms, preferably at least partially fluorinated 18 a (hydro)carbyl group (including alkylene or cycloalkylene), or a (per)fluoro(poly)oxyalkylene group comprising one or more catenary ether linkages; B: compounds comprising three carbon-carbon unsaturations, preferably selected from the group consisting of: (i) tri-substituted cyanurate compounds having the following general formula: wherein each R cy the same or different from each other and at each occurrence, are independently selected from H or a group -R rcy or -OR rcy wherein R rcy is a C1-C5 alkyl, possibly containing one or more halogens, and each J cy the same or different from each other and at each occurrence, are independently selected from a bond or a divalent hydrocarbon group optionally containing heteroatoms; (ii) - tri-substituted isocyanurate compounds having the following general formula: wherein each R isocy the same or different from each other and at each occurrence, are independently selected from H or a group -R risocy or -OR risocy wherein R risocy is a C1-C5 alkyl, possibly containing one or more halogens, and each J isocy the same or different from each other and at each occurrence, are independently selected from a bond or a divalent hydrocarbon group optionally containing heteroatoms; (iii) tri-substituted triazine compounds having the following general formula: wherein each R az the same or different from each other and at each occurrence, are independently selected from H or a group -R raz or -OR raz wherein R raz is a C1-C5 alkyl, possibly containing one or more halogens, and each J az the same or different from each other and at each occurrence, are independently selected from a bond or a divalent hydrocarbon group optionally containing heteroatoms; (iv) tri-substituted phosphite compounds having the following general formula: wherein each R ph the same or different from each other and at each occurrence, are independently selected from H or a group -R rph or -OR rph wherein R rph is a C1-C5 alkyl, possibly containing one or more halogens, and each J ph the same or different from each other and at each occurrence, are independently selected from a bond or a divalent hydrocarbon group optionally containing heteroatoms; (v) tri-substituted alkyltrisiloxanes having the following general formula: wherein each R si are the same or different from each other and at each occurrence are independently selected from H or a group -R rsi or -OR rsi wherein R rsi is a C1-C5 alkyl group, possibly containing one or more halogens, each R' si are the same or different from each other and at each occurrence are independently selected from a C1-C5 alkyl group, possibly containing one or more halogens, and each J si are the same or different from each other and at each occurrence are independently selected from a bond or a divalent hydrocarbon group optionally containing heteroatoms; (vi) N,N-disubstituted acrylamide compounds having the general formula: wherein each R an are the same or different from each other and at each occurrence are independently selected from H or a group -R ran or -OR ran wherein R ran is a C1-C5 alkyl group, possibly containing one or more halogens, and each J an are the same or different from each other and at each occurrence are independently selected from a bond or a divalent hydrocarbon group optionally containing heteroatoms; C: compounds (U) comprising four or more carbon-carbon unsaturations, which are preferably selected from tri(diallylamine)-s-triazines having the formula: hexa-allyl phosphoramide, N,N,N',N'-tetra-allyl terephthalamide, and N,N,N',N'-tetra-allyl malonamide.

9. The fluoroelastomer composition of any preceding claim, wherein, The one or more curing co-agents are present in an amount of 0.1 to 20 phr, preferably 1 to 15 phr, more preferably 1 to 10 phr.

10. The fluoroelastomer composition of any preceding claim, wherein, The fluoroelastomer A is obtained from an emulsion polymerization process carried out in the absence of a fluorinated surfactant.

11. The fluoroelastomer composition of claim 10, wherein, The emulsion polymerization process is carried out in the presence of a redox initiation system comprising at least one organic free radical initiator and at least one compound bearing at least one sulfinic acid group.

12. A process for the manufacture of the composition according to claims 1-11, comprising the steps of: (i) the fluoroelastomer A as defined in claim 1 made with an emulsion polymerization process carried out in the absence of a fluorinated surfactant, Use of the fluoroelastomer composition according to any one of the preceding claims for the manufacture of a shaped article, (ii) mixing the fluoroelastomer A with - one or more organic peroxides, - one or more curing co-agents and - one or more fatty acid salts.

13. A process for the manufacture of a shaped article, the process comprising curing the fluoroelastomer composition according to any one of claims 1 to 11.

14. A cured article obtained from the composition according to any one of claims 1 to 11, the cured article being selected from the group consisting of sealing articles, including O (square) -rings, gaskets, pads, spacers, shaft seals, valve stem seals, piston rings, crankshaft seals, camshaft seals, and oil seals, or can be tubing and pipes, in particular flexible hoses or other articles, including conduits for the delivery of hydrocarbon fluids and fuels.

15. Use of one or more fatty acid salts in a composition comprising: (i) a fluoroelastomer (fluoroelastomer A), the fluoroelastomer A: - obtained from an emulsion polymerization process carried out in the absence of a fluorinated surfactant, - comprising iodine and / or bromine atoms, and - having a backbone comprising 40-80% by moles of repeating units derived from vinylidene fluoride (VDF), 20-60% by moles of repeating units derived from one or more additional fluorinated monomers different from VDF, (ii) one or more organic peroxides, (iii) one or more curing co-agents, for reducing the c-set value of a cured material obtained from curing the composition.

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