CURABLE FLUOROELASTOMER COMPOSITION

Abstract

Provided herein are curable fluoroelastomer compositions comprising at least one fluoroelastomer comprising copolymerized units of a nitrile group-containing cure site monomer, a cure system comprising at least two different dihydrazides, and optionally at least one additive. Also provided are preforms comprising the curable compositions, methods for curing the fluoroelastomer compositions, compositions that are the cured product of the curable fluoroelastomer compositions, and articles comprising the cured fluoroelastomer compositions.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority under 35 U.S.C. 365 to U.S. Provisional Patent Application No. 62 / 844,334, filed May 7, 2019, the entire contents of which are incorporated herein by reference.

[0002] Described herein are curable fluoroelastomer compositions, more particularly, curable fluoroelastomer compositions that include a mixture of two or more dihydrazide curatives. [Background technology]

[0003] In order to more fully describe the technical field to which the present invention pertains, several patents and publications are cited herein, the entire disclosures of each of which are incorporated herein by reference.

[0004] Fluoroelastomers have achieved significant commercial success and are used in a wide range of applications that encounter harsh environments, especially end uses that involve exposure to high temperatures and highly reactive chemicals.For example, these polymers are often used in the oil and gas industry as downwell bit seals, where drilling assemblies are exposed to aqueous environments at high temperatures and high pressures, and then rapidly returned to atmospheric pressure.However, there is a continuing need for seals for use in these extreme environments that exhibit a desirable combination of low temperature sealing performance combined with rapid gas decompression resistance and hot water resistance.

[0005] The outstanding properties of fluoroelastomers arise primarily from the stability and inertness of the copolymerized fluorinated monomer units that make up the majority of the polymer backbone in these compositions. Such monomers include vinylidene fluoride, hexafluoropropylene, tetrafluoroethylene, and perfluoro(alkyl vinyl) ethers. To fully develop the elastomeric properties, fluoroelastomers are typically crosslinked, i.e., vulcanized or cured. For this purpose, a small percentage of cure site monomers are copolymerized with the fluorinated monomer units. Particularly preferred are cure site monomers that contain at least one nitrile group, such as perfluoro-8-cyano-5-methyl-3,6-dioxa-1-octene. The cure site crosslinks the fluoropolymer by reacting with one or more curing agents, such as diamine compounds, bisphenol compounds, and peroxide compounds. Such polymers and compositions are described in U.S. Pat. Nos. 4,281,092; 4,394,489; 5,789,489; and 5,789,509, as well as WO 2011 / 084404.

[0006] Other nitrogen-containing nucleophilic compounds have been used to crosslink fluoroelastomers with nitrile group cure sites. See, for example, U.S. Patent No. 6,638,999 B2. Some of these curatives are prone to scorch (i.e., crosslinking may begin before final molding of the composition), while others volatilize at rubber mixing temperatures. Summary of the Invention [Problem to be solved by the invention]

[0007] It has been discovered that when a mixture of two or more different dihydrazide curatives is used as a cure system for a fluoroelastomer composition, the cured composition can exhibit improved physical properties, particularly for use in the oil and gas industry in downhole applications. [Means for solving the problem]

[0008] Thus, provided herein is a curable fluoroelastomer composition comprising at least one fluoroelastomer comprising copolymerized units of a nitrile group-containing cure site monomer, a cure system comprising at least two different dihydrazides, and optionally at least one additive. Also provided are a method of curing the fluoroelastomer composition, a preform comprising the curable fluoroelastomer composition, a cured fluoroelastomer composition that is the product of crosslinking the curable fluoroelastomer composition, and an article comprising the cured fluoroelastomer composition. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Abbreviation "phr" means parts per hundred parts of fluoroelastomer (rubber); those skilled in the art use and recognize this term of measurement. For example, 3 parts of a component per 100 parts of fluoroelastomer would be written as 3 phr. In the compounds, procedures, and articles described herein, phr is based on 100 parts fluoroelastomer A.

[0010] "t90" means the time in minutes required for the torque to reach 90% of its maximum at a given temperature when a force is applied to a curable fluoroelastomer composition, as measured with a working die rheometer or similar instrument.

[0011] "g" stands for grams.

[0012] "MPa" means megapascal.

[0013] "%" refers to the term percent.

[0014] "Mol %" means mole percent.

[0015] definition To further define and explain the present disclosure, the following definitions are used herein. These definitions apply to terms used throughout this specification, unless limited in specific instances.

[0016] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In case of conflict, the present specification, including definitions expressly set forth herein, will control.

[0017] Unless otherwise stated in expressly defined context, all percentages, parts, ratios and similar amounts used herein are defined by weight.

[0018] When materials, methods, or mechanical devices are described herein with the term "known to those skilled in the art," "conventional," or equivalent words or phrases, this term is intended to mean that materials, methods, and mechanical devices that are conventional at the time of the filing of this application are covered by the description. Also included are materials, methods, and mechanical devices that are not currently conventional, but that would become recognized in the art as suitable for similar purposes.

[0019] As used herein, the terms "comprises," "comprising," "includes," "including," "containing," "characterized by," "has," "having," or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a process, method, article, or apparatus that includes a list of elements is not necessarily limited to only those elements and can include other elements that are not expressly listed or that are inherent to such process, method, article, or apparatus.

[0020] The transitional phrase "consisting of" normally closes a claim to the inclusion of materials other than those recited, except for incidental impurities, and excludes any element, step, or ingredient not embodied in the claim. When the phrase "consists of" or "consisting of" appears in a clause in the body of a claim rather than immediately following a preamble, it limits only the elements recited in that clause; other elements are not excluded from the claim as a whole.

[0021] The transitional phrase "consisting essentially of" limits the scope of a claim to those materials or steps embodied therein and which do not materially affect the basic and novel characteristics of the claimed invention. A 'consisting essentially of' claim represents a compromise between a closed claim written in a 'consisting of' format and a fully open claim drafted in a 'comprising' format.

[0022] In addition, the term "consisting essentially of" as used herein means a composition that contains more than 95% by weight or more than 99% by weight of the listed components, based on the total weight of the composition. Furthermore, optional additives and trace impurities as defined herein, at levels appropriate for such additives, are not excluded from the composition by the term "consisting essentially of". Thus, a composition to which this term applies may contain one or more other components or additives, such as those described below, including any carriers that may be introduced together with the other components or additives. In these amounts, the other components, additives and their carriers do not change the basic and novel characteristics of the phases or compositions described herein.

[0023] When a composition, process, structure, or portion of a composition, process, or structure is described herein using open-ended terminology such as "comprising," unless otherwise specified, the description also includes embodiments that "consist essentially of" or "consist of" the composition, process, structure, or portion of the composition, process, or structure.

[0024] In this regard further, certain features of the invention that are described herein in the context of separate embodiments may also be provided in combination in a single embodiment. Conversely, various features of the invention that are, for brevity, described in the context of a single embodiment, may also be provided separately or in any subcombination.

[0025] The articles "a" and "an" may be utilized in connection with various elements and components of the compositions, methods, or structures described herein. This is merely for convenience and to give a general sense of the composition, method, or structure. Such descriptions include "one or at least one" of the element or component. Furthermore, as used herein, the singular article also includes the description of a plurality of elements or components, unless it is clear from the specific context that a plurality is excluded.

[0026] Furthermore, unless expressly stated to the contrary, the conjunction "or" means an inclusive or, not an exclusive or. For example, the condition "A or B" is satisfied by any one of the following: A is true (or exists) and B is false (or does not exist), A is false (or does not exist) and B is true (or exists), and A and B are both true (or exist). Exclusive "or" is made clear herein by terms such as "either A or B" and "one of A or B."

[0027] The term "about" means that amounts, sizes, formulations, parameters, and other quantities and characteristics are not, and need not be, exact, but may be approximate and / or larger or smaller, as appropriate, to reflect tolerances, conversion factors, rounding, measurement errors, and the like, as well as other factors known to those of skill in the art. In general, an amount, size, formulation, parameter, or other quantity or characteristic is "about" or "approximate" whether or not it is expressly stated to be such.

[0028] Moreover, the ranges set forth herein include their endpoints unless otherwise specified in limited circumstances. Furthermore, when an amount, concentration, or other value or parameter is given as a range, one or more preferred ranges, or a list of an upper preferred value and a lower preferred value, this should be understood to specifically disclose all ranges formed from any pair of any range upper limit or preferred value and any range lower limit or preferred value, regardless of whether such pair is separately disclosed. The scope of the present invention is not limited to the specific values ​​recited when defining a range, but rather includes all real numbers within the range, including its endpoints.

[0029] In addition, any recitation of a variation of materials, chemicals, methods, steps, values, ranges, etc. of the processes, compounds, and articles described herein specifically includes combinations of that variation with other materials, methods, steps, values, ranges, etc. that constitute or form the processes, compounds, and articles described herein, whether identified as preferred or not.

[0030] The term "perfluoro", as used herein alone or in combination, such as in "perfluoroelastomer" and "perfluorovinyl ether", refers to a molecule or moiety in which all hydrogen atoms have been replaced with fluorine atoms. For example, the term "perfluoroacetone" refers to the compound (CF3)2C=O, and the term "perfluorinated olefin" refers to a linear, branched, or cyclic structure that contains at least one unsaturated double bond and that contains fluorine and carbon atoms but no hydrogen atoms.

[0031] As used herein, the term "fluoro", when used alone or in combination herein, such as, for example, "fluoroelastomer" and "fluorovinyl ether", means a molecule or moiety in which at least one fluorine atom is substituted for a hydrogen atom. The prefix "fluoro", when placed as a prefix before a chemical name, specifically includes "perfluoro" chemicals. Thus, the prefix "fluoro", when placed before a chemical name, refers to both "fluoro" and "perfluoro" entities.

[0032] As used herein, the term "alkyl" refers to linear, branched, or cyclic hydrocarbon structures and combinations of two or more of these structures. The term "alkyl" does not include unsaturated or aromatic structures. Examples of linear alkyl groups include methyl, ethyl, propyl, butyl, pentyl, and hexyl groups. Examples of branched alkyl groups include, for example, sec-butyl, tert-butyl, and isopropyl groups. Examples of cyclic hydrocarbon groups include cyclopropyl, cyclopentyl, cyclohexyl, cyclobutyl, and cyclooctyl groups.

[0033] As used herein, the term "alkoxy" or "alkoxyl" refers to an alkyl group connected by a single bond to an oxygen atom. The other bond of the oxygen atom is attached to a carbon atom. Examples include methoxy, ethoxy, propoxy, isopropoxy, butoxy, cyclopropyloxy, cyclopentyloxy, and cyclohexyloxy.

[0034] The term "cured", as used herein, whether alone or in combination, such as "cured", "curing" or "curable", is synonymous with the terms "crosslinked" and "vulcanized" and is used interchangeably to refer to a polymer that contains reactive sites that react to form covalent bonds, at least some of which link two polymer molecules. The curable fluoroelastomer compositions described herein can be cured to form sufficient crosslinks such that the resulting cured fluoroelastomer composition cannot be thermally processed, such as molded or extruded. That is, when the curable fluoroelastomer composition is exposed to curing conditions, such as in a compression molding process, it is thereby cured to form an article, which cannot be remolded to a substantially different form or shape, configuration or structure. In other words, the cured fluoroelastomer composition is a thermoset material.

[0035] The material resulting from the curing process is a "cured" material, i.e., a bulk fluoroelastomer, or an article as defined herein above. Curing results in a compound that takes the form or shape or configuration or structure of an article. Cured articles of the compounds described herein include, but are not limited to, blocks, slabs, O-rings, tubes, seals, and gaskets.

[0036] The term "cure" also expressly includes different degrees of crosslinking of the curable composition, for example, by controlling the stoichiometry of the cure sites or crosslinkers, or by controlling the curing conditions, such as time, temperature, or pressure. It may also be desirable to modify certain physical properties of the cured composition by varying the extent of curing. In other words, the curable fluoroelastomer compositions described herein may be partially crosslinked, fully crosslinked, or substantially fully crosslinked, depending on the desired properties of the cured fluoroelastomer composition or article.

[0037] A cured fluoroelastomer composition or article comprising the cured fluoroelastomer composition may be "post-cured", i.e., subjected to additional curing conditions that provide for further cure. A curable composition that has been subjected to more than one cure cycle, i.e., a "post-cured" composition, may also be described as "cured".

[0038] overview The curable fluoroelastomer compositions described herein comprise at least one fluoroelastomer having nitrile group cure sites and a cure system comprising at least two different dihydrazide curatives. Preferably, the curable fluoroelastomer compositions comprise the following: A) at least one fluoroelastomer comprising copolymerized units of a nitrile group-containing cure site monomer; B) a cure system comprising a mixture of two or more different dihydrazides; and C) Optionally, at least one additive Includes.

[0039] Additionally provided are preforms comprising the curable fluoroelastomer composition, methods for curing the curable fluoroelastomer composition, the resulting cured fluoroelastomer composition, and articles comprising the cured fluoroelastomer composition.

[0040] A) Fluoroelastomer The curable fluoroelastomer preferably comprises from 25 to 70 parts by weight, based on the total weight of the curable fluoroelastomer, of copolymerized units of at least one first monomer that is a fluorinated alkene. Suitable first monomers include, but are not limited to, 1,1-difluoroethylene (C2H2F2), hexafluoro-propylene (HFP), tetrafluoroethylene (TFE), 1,2,3,3,3-pentafluoropropene (1-HPFP), 1,1,3,3,3-pentafluoropropene (2-HPFP), chlorotrifluoroethylene (CTFE), 1,1,2-trifluoroethylene, 1-fluoroethylene, and combinations of two or more of these first monomers. The curable fluoroelastomer further comprises copolymerized residues of a second monomer that is a fluorovinyl ether, and copolymerized units of a cure site monomer. Optionally, the curable fluoroelastomer (A) may further comprise copolymerized units of one or more additional copolymerized monomers different from said first monomer, said second monomer, and said cure site monomer.

[0041] Suitable fluorine-containing vinyl ethers for use as monomer (ii) to prepare fluoroelastomers include, but are not limited to, fluoro(alkyl vinyl) ethers. Perfluoro(alkyl vinyl) ethers (PAVEs) are preferred. Suitable perfluoro(alkyl vinyl) ethers for use as monomers include those of the formula: CF2 = CFO(R f’ O) n (R f” O) m R f (I) (In the formula, R f’ and R f” are different linear or branched perfluoroalkylene groups of 2 to 6 carbon atoms, m and n are integers independently selected from the range of 0 to 10, R f is a perfluoroalkyl group of 1 to 6 carbon atoms.

[0042] A preferred class of perfluoro(alkyl vinyl) ethers includes compositions of the formula: CF2=CFO(CF2CFXO) n R f (II) (wherein X is F or CF3, n is an integer ranging from 0 to 5, and Rf is a perfluoroalkyl group of 1 to 6 carbon atoms).

[0043] A more preferred class of perfluoro(alkyl vinyl) ethers includes compositions of the formula: CF3O-(CF2O) n -CF2CF2-OCF=CF2(III) (In the formula, n is an integer ranging from 0 to 5.) A more preferred example of a perfluorinated ether is 1-[2-[difluoro(trifluoromethoxy)methoxy]-1,1,2,2-tetrafluoroethoxy]-1,2,2-trifluoroethene.

[0044] An even more preferred class of perfluoro(alkyl vinyl) ethers includes those where n is 0 or 1 and R f contains 1, 2 or 3 carbon atoms. Examples of such perfluorinated ethers include, but are not limited to, perfluoro(methyl vinyl) ether (PMVE), perfluoro(ethyl vinyl) ether (PEVE), and perfluoro(propyl vinyl) ether (PPVE).

[0045] Other suitable perfluoro(alkyl vinyl) ethers include those of the formula: CF2 = CFO[(CF2)mCF2CFZO]nR f (IV) (In the formula, R f is a perfluoroalkyl group having 1 to 6 carbon atoms, m=0 or 1, n=0, 1, 2, 3, 4 or 5, and Z=F or CF3). A preferred member of this class is R f is C3F7, m=0, and n=1.

[0046] Additional perfluoro(alkyl vinyl) ether monomers include compounds of the formula: CF2=CFO[(CF2CF{CF3}O)n(CF2CF2CF2O)m(CF2)p]C x F2x+1(V) (wherein m and n are integers independently selected from the range of 0 to 10, p=0, 1, 2 or 3, and x=1, 2, 3, 4 or 5.) Preferred members of this class include compounds where n=0 or 1, m=0 or 1, and x=1.

[0047] Other examples of useful perfluoro(alkyl vinyl) ethers include those of the formula: CF2 = CFOCF2CF(CF3)O(CF2O) m C n F 2n+1 (VI) (wherein n=1, 2, 3, 4 or 5, m=1, 2 or 3, preferably n=1).

[0048] When copolymerized units of PAVE are present in the curable fluoroelastomer, the content of copolymerized PAVE units generally ranges from 25 to 75% by weight, preferably from 35 to 65% by weight, based on the total weight of the curable fluoroelastomer. When perfluoro(methyl vinyl) ether is used, the curable fluoroelastomer preferably contains 40 to 60% by weight of copolymerized PMVE units.

[0049] The curable fluoroelastomer generally further comprises a nitrile group-containing cure site monomer in an amount of 0.1 to 5 weight percent. This range is preferably 0.5 to 3.5 weight percent, more preferably 1 to 3 weight percent, based on the total weight of the curable fluoroelastomer. Suitable cure site monomers include nitrile-containing perfluorinated olefins and nitrile-containing perfluorinated vinyl ethers. Useful nitrile-containing cure site monomers include those of the formula shown below: CF2=CF-O(CF2)n-CN (VII) (wherein n is selected from the range of 2 to 12, preferably from the range of 2 to 6); CF2=CF-O[CF2-CFCF3-O] n -CF2-CFCF3-CN (VIII) wherein n is 0, 1, 2, 3 or 4, preferably 0, 1 or 2; CF2=CF-[OCF2CFCF3]xO-(CF2)n-CN (IX) where x=1 or 2 and n=1, 2, 3 or 4; and CF2=CF-O-(CF2) n -O-CF(CF3)CN (X) where n=2, 3 or 4.

[0050] Preferred are nitrile-containing perfluorinated vinyl ethers of formula (VIII). More preferred cure site monomers are perfluoropolyethers having nitrile groups and trifluorovinyl ether groups. Even more preferred cure site monomers are CF2=CFOCF2CF(CF3)OCF2CF2CN (XI) That is, perfluoro(8-cyano-5-methyl-3,6-dioxa-1-octene) or 8-CNVE.

[0051] Suitable optional additional monomers include, but are not limited to, hydrocarbon olefins. Suitable hydrocarbon olefins include, but are not limited to, ethylene and propylene. Cure site monomers that do not contain nitrile groups, such as isomers of trifluoropropylene (TFP) and isomers of bromotetrafluorobutene (BTFB), are also suitable additional monomers. When copolymerized units of hydrocarbon olefins are present in the curable fluoroelastomer, they are present in a concentration of 0.1-30 wt%, or 4-30 wt%, or 0.1-25 wt%, 0.1-20 wt%, 0.1-15 wt%, 0.1-10 wt%, or 0.1-5 wt%, based on the total weight of the curable fluoroelastomer. One suitable curable fluoroelastomer with optional additional monomers is TFE / Propylene / BTFB / TFP / CNVE.

[0052] Preferably, the curable fluoroelastomer (A) is one of the following: i) at least one first monomer which is a perfluorinated olefin; ii) at least one second monomer which is a perfluorovinyl ether; and iii) one or more nitrile-containing cure site monomers selected from the group consisting of nitrile-containing perfluorinated olefins and nitrile-containing perfluorinated vinyl ethers; Contains copolymerized units of:

[0053] The amounts of copolymerized residues of all comonomers in the curable fluoroelastomer are complementary, in other words the sum of the weight percentages of copolymerized residues of all comonomers in the curable fluoroelastomer is 100 weight %.

[0054] Suitable fluoroelastomers may be prepared by methods known in the art, such as those described in US Pat. No. 5,789,489.

[0055] B) Curing system The cure system used in the curable fluoroelastomer composition comprises a curing agent mixture of at least two different dihydrazides. Suitable dihydrazides are described in U.S. Patents 8,765,875 and 8,765,876, both issued to Bish et al. Preferred dihydrazides include, but are not limited to, malonic acid dihydrazide, succinic acid dihydrazide, adipic acid dihydrazide, oxalyl dihydrazide, 1,3-imidazolidinedipropanoic acid, 4-(1-methylethyl)-2,5-dioxo-, 1,3-dihydrazide, tetradecanoic acid, 1,14-dihydrazide, hexanedioic acid, 2,2,3,3,4,4,5,5-octafluoro-, 1,6-dihydrazide, isophthalic acid dihydrazide, carbonic acid dihydrazide, carbonic acid dihydrazide dihydrochloride, 1,2-hydrazinedicarboxylic acid, dihydrazide, diaminobiuret, and p-phenylene-bis-semicarbazide. More preferred dihydrazides include isophthalic acid dihydrazide and oxalyl dihydrazide.

[0056] The combination of dihydrazides is selected to balance or optimize the properties of the cured fluoroelastomer.For example, a dihydrazide curing agent that acts on a fluoroelastomer composition to produce a cured fluoroelastomer with a given hardness and a given elongation at break can be combined with a second different dihydrazide curing agent that acts on the same fluoroelastomer to produce a cured fluoroelastomer with a similar hardness and a different elongation at break.For example, the cured fluoroelastomer resulting from a combination of dihydrazides acting on the same fluoroelastomer composition can have an elongation at break that is intermediate between those of the cured fluoroelastomers produced from the individual dihydrazides.

[0057] A hardener mixture of two different dihydrazides is preferred. The two dihydrazides may be combined in a weight ratio of about 99:1 to about 1:99; about 49:1 to about 1:49; about 19:1 to about 1:19; about 9:1 to about 1:9; about 5:1 to about 1:5; about 4:1 to about 1:4; about 3:1 to about 1:3. A weight ratio of about 3:1 to about 1:2 is preferred. More preferably, the two different dihydrazides are isophthalic dihydrazide and oxalyl dihydrazide in a weight ratio of isophthalic dihydrazide:oxalyl dihydrazide ranging from about 3:1 to about 1:2 or about 1:1 to about 2:1.

[0058] Optionally, a cure accelerator may be used in combination with the dihydrazide curing agent, such as a compound that releases ammonia at the cure temperature. Examples and suitable amounts of compounds that decompose to release ammonia at the cure temperature are described in U.S. Pat. No. 6,281,296 B1 and U.S. Patent Application Publication No. 2011 / 00095969.

[0059] Optionally, in addition to the dihydrazide, another curing agent commonly used to crosslink fluoroelastomers with nitrile group cure sites may be used. Examples of such other curing agents include, but are not limited to, diaminobisphenol AF, 2,2-bis(3-amino-4-anilinophenyl)hexafluoropropane, mono- or bis-amidines, mono- or bis-amidrazones, mono- or bis-amidoximes, or organic peroxides plus coagents.

[0060] The total concentration of the cure system in the fluoroelastomer composition may range from about 0.1 to about 4 phr, preferably 0.5 to 2 phr. For example, a composition containing 100 parts by weight of fluoroelastomer further contains 0.5 phr of oxalyl dihydrazide and 0.8 phr of isophthalic dihydrazide for a total of 1.3 phr of cure system per 100 phr, and the ratio of weight of isophthalic dihydrazide to weight of oxalyl dihydrazide is 1.6:1.

[0061] C) Optional Additives Optional additives that can be used in the fluoroelastomer composition to improve or optimize various physical properties include, but are not limited to, carbon black, fluoropolymer micropowders, stabilizers, plasticizers, lubricants, fillers (e.g., mineral fillers such as silica, alumina, aluminum silicate, barium sulfate, titanium dioxide), coagents and processing aids. Suitable optional additives have sufficient thermal, chemical or mechanical stability to be incorporated into the curable fluoroelastomer composition under those processing conditions, including cure conditions, or to function satisfactorily under the intended use conditions of the cured fluoroelastomer composition.

[0062] Examples of suitable carbon blacks include carbon blacks having particle sizes ranging from about 10 nm (small) to 500 nm (large). Examples of small particle size carbon blacks include SAF carbon black, Spheron 6400®, and FEF carbon. Highly reinforced blacks having an average particle size of about 14 nm and designated N110 in Group No. 1 by ASTM D1765. Large carbon black particles describe a specific classification of carbon blacks having an average particle size of at least about 100 nm to about 500 nm as determined by ASTM D3849, as discussed in U.S. Pat. No. 5,554,680. Examples include MT blacks (medium pyrolytic blacks) designated N-991, N-990, N-908, and N-907, as well as large particle size furnace blacks. MT blacks are preferred.

[0063] Blends of small and large particle size carbon blacks may also be used, for example the larger carbon black particles in the blend of different size carbon black particles may be present in an amount ranging from about 40 to 60 phr and the smaller carbon black particles may range from 2 to 8 phr.

[0064] If present, the total concentration of the optional additives may range from about 0.1 to 200 phr, preferably from about 1 to 100 phr.

[0065] Preparation of Curable Fluoroelastomer Compositions The curable fluoroelastomer composition can be prepared by mixing the fluoroelastomer, the cure system, and optional additives using standard rubber compounding procedures. For example, the ingredients can be mixed on a two-roll rubber mill, in an internal mixer (e.g., a Banbury™ internal mixer), or in an extruder.

[0066] Preforms and Articles The curable fluoroelastomer composition can be formed into objects of various shapes by physical means without undergoing any chemical reaction. These uncured objects are known as "preforms". For example, the curable composition can be formed into a preform by any suitable method, such as rolling, molding, die cutting or extrusion. The preform can be subjected to curing conditions, such as heat or pressure, to form a cured article.

[0067] Alternatively, the curable fluoroelastomer composition may be formed into a blank having the shape of, for example, a disk, slab, or block. In addition, the blank may have no particular shape, provided that the curable composition is cured in the same form in which it is produced or compounded. The blank is cured and then machined to form an article comprising the cured fluoroelastomer composition. The shape and size of the curable composition before curing is determined by the dimensions of the machined article.

[0068] The cured article or blank may be of a similar shape and size to the preform, or uncured blank from which it is made, although dimensions may vary between the two.

[0069] In another process for producing articles comprising the cured fluoroelastomer composition, the curable fluoroelastomer composition can be molded or crosslinked (i.e., cured) by application of heat, pressure, or both heat and pressure to produce a cured article. Molding is generally followed by a post-cure cycle during which the press-cured composition is heated at elevated temperatures, e.g., above 300° C., for several hours. When compression molding is utilized, a press-cure cycle is preferably also used.

[0070] The cured fluoroelastomer compositions have excellent thermal stability, sealing properties and hot water resistance, as well as a favorable balance of other properties including elongation at break, modulus, hardness, compression set and volume swell. Preferably, the cured fluoroelastomer compositions and blanks and articles comprising the cured fluoroelastomer compositions have a volume swell of less than 5%, 8%, 10% or 20% measured according to ASTM D1414:2015, or an elongation at break of at least 40%, 43%, 46%, 50%, 60%, 70%, 80%, 90% or 100% measured according to ASTM D412-06a:2013 after 70 hours exposure to water at 225°C.

[0071] The curable fluoroelastomer compositions are useful, for example, in the manufacture of gaskets, tubing, and seals. Cured articles made from the curable fluoroelastomer compositions are particularly useful in the oil and gas industry for downwell applications where drilling assemblies are exposed to aqueous environments at high temperatures and where pressures can fluctuate rapidly.

[0072] The following examples are provided to further illustrate the present invention. These examples, which indicate preferred modes presently contemplated for carrying out the invention, are intended to illustrate, but not to limit, the invention. EXAMPLES

[0073] The following examples and comparative examples illustrate the use of the dihydrazide cure systems described herein in curable fluoroelastomer compositions. In this section, unless otherwise specified in limited circumstances, all parts are based on 100 phr and the fluoroelastomer is a rubber.

[0074] material FFKM: A perfluoroelastomer containing 61.9 mole percent copolymerized units of TFE, 37.4 mole percent copolymerized units of PMVE, and 0.7 mole percent copolymerized units of 8-CNVE was prepared by the general process described in U.S. Pat. Nos. 5,789,489, 7,977,426, and 7,999,049. Oxalyl dihydrazide (CAS # 996-98-5) was obtained from Sigma-Aldrich, St. Louis, Missouri, USA. Isophthalic dihydrazide (CAS # 2760-98-7) was obtained from TCI America, Portland, Oregon, USA. Carbon Black: Thermal carbon black having an average particle size of 280 nm, available as Thermax® N990 from Cancarb of Medicine Hat, Alberta, Canada. Plasticizer: A perfluoropolyether available as Krytox® XHT-1000 from The Chemours Company FC, LLC, of ​​Wilmington, Delaware.

[0075] Test Method Elastic modulus / elongation at break / tensile strength at break Modulus, elongation at break, and tensile strength at break were determined according to ASTM D412-06a:2013. Dumbbell-shaped specimens (Figure 2 ASTM D 412-06aVol.09-01, Die "C") were cut from 2 mm (0.8 in) thick molded and cured slabs of fluoroelastomer composition. Samples were conditioned at 23°C and 50% relative humidity for 3 hours prior to testing.

[0076] An Instron Single Station Tensile Machine model #5564 equipped with a mechanical grip-type contact extensometer programmed with Instron Bluehill version 2.6 software was used for testing at a crosshead speed of 500 mm / min at 23° C. A minimum of three specimens were tested for each composition, and the median value of each property is reported.

[0077] Shore A hardness Shore A hardness was determined according to ASTM D2240-05:2010. Dumbbell-shaped specimens (Figure 2 ASTM D 412-06aVol.09-01, Die "C") were cut from molded and cured slabs of the fluoroelastomer compositions. The specimens were conditioned at 23°C and 50% relative humidity for 3 hours prior to testing.

[0078] Testing was performed on a New Age Hardness Tester fitted with a Shore A Head at a temperature of 23°C with a descent speed of the indenter on the specimen of 3.2 mm / sec. Three measurements were made on a four-ply laminate of dumbbell specimens die-cut from molded slabs of 2 mm (0.08 in) thickness. The first measurement was made at the center of the specimen. The specimen was then rotated 180 degrees and a second measurement was made at the center of the dumbbell. The specimen was turned over and a final measurement was made at the center of the dumbbell. The median of the triplicate results is reported in the table.

[0079] Compression set Compression set at constant deflection (25%) was determined according to ASTM D395-14:2014. The specimen type was AS-214 O-rings. From this, a small portion of each O-ring was cut and removed so that the inner surface was exposed to the same environment as the outer surface. For each composition, three AS-214 O-ring specimens were compressed and aged at elevated temperature in air or water. After aging, the specimens were removed from their compression apparatus, allowed to cool to room temperature, and the heights were measured to determine the relationship between their initial height before compression and aging (h0) and their height after compression and aging (h), expressed as a percentage (h / h0). * The median of the three results for each composition is reported in the table.

[0080] Volume swelling percentage Percent volume swelling was measured on AS-214 O-rings according to ASTM D471-12a:2012. Prior to testing, the weights of the O-rings were measured in air at 23°C and in an ethanol / water solution with a specific gravity of 0.820+ / -0.001. The O-rings were then aged in distilled water for 70 hours at 225°C using the aging procedure of ASTM D1414:2015. After aging in distilled water, the O-rings were reweighed in air and in the ethanol / water solution to determine the percentage volume swelling. Archimedes' principle was used to calculate the volume change, whereby the density of the article can be determined by taking the weight of the article in air and the weight of that article in a fluid of known density. The percent volume swelling after aging was calculated according to the equation in D471-12a:2012 section 17.2(3).

[0081] Preparation of Examples and Comparative Examples The curable fluoroelastomer compositions were compounded on a two-roll rubber mill in the compositions and proportions shown in Tables 1 and 2. O-rings for compression set and volume swell testing were prepared from these curable fluoroelastomer compositions by press curing at 200°C for t90+5 minutes, followed by post curing at 305°C for 26 hours in a nitrogen atmosphere. The physical properties of the cured fluoroelastomer compositions are shown in Tables 1 and 2.

[0082] [Table 1]

[0083] Table 1 shows the properties of the cured fluoroelastomer composition E1, which contains a mixture of dihydrazides, compared to the properties of the fluoroelastomer compositions C1 and C2, which contain only a single dihydrazide as a curing agent. E1 contains about half the mass of each dihydrazide compared to each of C1 and C2. Based on this relationship, it was predicted that for E1, properties that depend on the cure site structure, such as volume swelling, would be approximately the average between the volume swelling of the C1 and C2 formulations. However, the measured volume swelling of E1 is significantly less than the average volume swelling expected based on C1 and C2. Thus, the measured volume swelling of E1 is unexpectedly small compared to the volume swelling of C1 and C2, while maintaining a balance of other favorable properties, such as elongation.

[0084] [Table 2]

[0085] Table 2 shows the properties of cured fluoroelastomer composition E2 containing a mixture of dihydrazides with different ratios of isophthalic dihydrazide to oxalyl dihydrazide, compared to those of fluoroelastomer compositions C3 and C4 containing only a single dihydrazide as a curing agent. The volumetric swelling of E2 is significantly less than that expected based on C3 and C4. Thus, the measured volumetric swelling of E2 is unexpectedly small compared to that of C3 and C4, while maintaining a balance of other favorable properties such as elongation.

[0086] While certain preferred embodiments of the present invention have been described and specifically exemplified above, it is not intended that the invention be limited to such embodiments. Various modifications may be made without departing from the scope and spirit of the invention as set forth in the following claims.

Claims

1. A) at least one fluoroelastomer comprising copolymerized units of a nitrile group-containing cure site monomer, The at least one fluoroelastomer is i) at least one fluorinated olefin selected from the group consisting of tetrafluoroethylene, hexafluoropropylene, and a combination of tetrafluoroethylene and hexafluoropropylene; ii) at least one fluorovinyl ether selected from the group consisting of perfluoro(methyl vinyl) ether; perfluoro(ethyl vinyl) ether; perfluoro(propyl vinyl) ether; CF3O-(CF2O)n-CF2CF2-OCF=CF2, where n is 0, 1, 2, 3, 4, or 5; and combinations of two or more of perfluoro(methyl vinyl) ether; perfluoro(ethyl vinyl) ether; perfluoro(propyl vinyl) ether; and CF3O-(CF2O)n-CF2CF2-OCF=CF2, where n is 0, 1, 2, 3, 4, or 5; and iii) a fluoroelastomer comprising copolymerized units of a nitrile group-containing perfluorinated olefin and at least one nitrile group-containing cure site monomer selected from the group consisting of perfluoro(8-cyano-5-methyl-3,6-dioxa-1-octene); B) a curing system comprising at least two different dihydrazides selected from the group consisting of isophthalic dihydrazide and oxalyl dihydrazide, wherein the weight ratio of isophthalic dihydrazide to oxalyl dihydrazide is in the range of 1:1 to 2:1; and optionally C) at least one additive; 1. A curable fluoroelastomer composition comprising:

2. 2. The curable fluoroelastomer composition of claim 1, wherein the at least one additive is present and comprises one or more additives selected from the group consisting of carbon black, lubricants, fillers, fluoropolymer micropowders, stabilizers, plasticizers, and processing aids.

3. 3. The curable fluoroelastomer composition of claim 1 or 2, wherein said at least one additive comprises at least one filler selected from the group consisting of silica, alumina, aluminum silicate, barium sulfate, titanium dioxide, and combinations of two or more of silica, alumina, aluminum silicate, barium sulfate, and titanium dioxide.

4. A cured fluoroelastomer composition which is the cured product of the curable fluoroelastomer composition of any one of claims 1 to 3.

5. 5. The cured fluoroelastomer composition of claim 4 having a volume swell of less than 10% measured according to ASTM D1414:2015 after exposure to water at 225°C for 70 hours.

6. An article comprising the cured fluoroelastomer composition of claim 4 or 5.

7. 7. The article of claim 6 in the form of a gasket, tube, seal or O-ring.

8. 8. The cured article of claim 6 or 7, having a volume swell of less than 10% as measured according to ASTM D1414:2015 after exposure to water at 225° C. for 70 hours.

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