Fluoroelastomer compounds

Abstract

A fluoroelastomer compounds containing specific types of carbon black, and cured articles formed from the compounds. The compounds show many useful properties for cured fluoroelastomer articles.

Description

FLUOROELASTOMER COMPOUNDSCROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of US Provisional Application No. 63 / 384,691, filed on November 22, 2022, the disclosure of which is hereby expressly incorporated herein by reference in its entirety.TECHNICAL FIELD

[0002] This invention relates to fluoroelastomer compounds comprising specific types of carbon black, and cured articles formed from the compounds.BACKGROUND

[0003] Fluoroelastomer (FKM or FPM) articles are characterized by high temperature resistance, acid and alkali resistance, oil resistance and chemical resistance. The properties of FKM articles arise largely because of the stability and inertness of the copolymerized monomers that make up the major portion of the polymeric backbone of these compounds. Such monomers include tetrafluoroethylene (TFE) and vinylidene fluoride (VDF). In order to develop elastomeric properties fully, elastomer compounds are typically crosslinked, i.e., vulcanized or cured. To this end, a small percentage of cure site monomer is optionally copolymerized with the monomers. Upon crosslinking, the cure site monomer reacts with a curing agent to form a crosslinked elastomer entity in the form of an article.

[0004] Mechanical properties such as low compression set are also required of fluoroelastomer articles for use of the article in various industries. Mechanical properties of cured elastomer compounds are normally adjusted by incorporating additives. Carbon black is used as an additive to improve mechanical properties. U.S. Pa. No. 10,472,494, which is hereby incorporated herein by reference in its entirety, discloses fluoroelastomer compounds containing specific types of curing agent and carbon black with average particle sizes at least about 100 nm to about 500 nm.

[0005] The final properties of the finished article may also depend on the type of curing agent selected. Thus the need to select an appropriate curing agent that will allow good processing and allow to achieve good mechanical properties.BRIEF SUMMARY

[0006] Fluoroelastomer compounds comprising specific types of carbon black showmany useful properties for cured fluoroelastomer articles.

[0007] The invention is directed to a compound comprising:(A) a fluoroelastomer in which the hydrogen content is at least 0.75 wt% or more,(B) a curing agent comprising an organic peroxide and polyfunctional coagent, and(C) one or more carbon black, at least one of the carbon black has between 20 and 40 m2 / g of statistical thickness surface area.

[0008] The invention is further directed to an article produced using the compound disclosed above.DETAILED DESCRIPTION

[0009] AbbreviationsThe claims and description herein are to be interpreted using the abbreviations and definitions set forth below.“h”, “hrs” refers to hours.“%” refers to the term percent.“mole %” refers to mole percent.“wt %” refers to weight percent.“°C” refers to degree Celsius.“parts” refers to parts by weight.“phr” refers to parts per hundred parts of fluoroelastomer (rubber); one of skill in the art uses and recognizes this term of measurement. For example, 3 parts of a component per 100 parts fluoroelastomer is written as 3 phr. In these compounds, processes, and articles described herein, phr is based on 100 parts of fluoroelastomer.“g” refers to grams.

[0010] DefinitionsAs used herein, the article “a” refers to one as well as more than one and does not necessarily limit its referent noun to the grammatical category of singular number.

[0011] As used herein, the terms “about” and “at or about”, when used to modify an amount or value, refers to an approximation of an amount or value that is more or less than the precise amount or value recited in the claims or described herein. The precise value of the approximation is determined by what one of skill in the art would recognize as an appropriate approximation to the precise value. As used herein, the term conveysthat similar values, not precisely recited in the claims or described herein, can bring about results or effects that are equivalent to those recited in the claims or described herein, for which one of skill in the art would acknowledge as acceptably brought about by the similar values.

[0012] As used herein, the term “article” refers to an unfinished or finished item, thing, object, or an element or feature of an unfinished or finished item, thing or object. As used herein, when an article is unfinished, the term “article” may refer to any item, thing, object, element, device, etc. that has a form, shape, configuration that may undergo further processing in order to become a finished article. When an article is unfinished, the term “preform” may refer to that form, shape, configuration, any part of which may undergo further processing to become finished. As used herein, when an article is finished, the term “article” refers to an item, thing, object, element, device, etc. that is in a form, shape, configuration that is suitable for a particular use / purpose without further processing of the entire entity or a portion of it.

[0013] An article may comprise one or more element(s) or subassembly(ies) that either are partially finished and awaiting further processing or assembly with other elements / subassemblies that together will comprise a finished article. In addition, as used herein, the term “article” may refer to a system or configuration of articles.

[0014] As used herein, the terms “comprises,” “comprising,” “includes,” “including,” “has,” “having” or any other variation of these, refer to a non-exclusive inclusion. For example, a process, method, article, or apparatus that comprises a list of elements is not limited to only the listed elements but may include other elements not expressly listed or inherent. Further, unless expressly stated to the contrary, “or” refers to an inclusive, not an exclusive, or. For example, a condition A or B is satisfied by any one of the following: A is true (or present) and B is false (or not present), A is false (or not present) and B is true (or present), and both A and B are true (or present). As used herein, the terms “comprises,” “comprising,” “includes,” “including,” “has,” “having”, “consisting essentially of’, and “consisting of’ or any other variation of these, may refer either to a non-exclusive inclusion or to an exclusive inclusion.

[0015] When these terms refer to a more exclusive inclusion, these terms limit the scope of a claim to those recited materials or steps that materially affect the novel elements of the recited invention.When these terms refer to a wholly exclusive inclusion, these terms exclude any element, step or component not expressly recited in the claim. As used herein, terms that describe molecules or polymers follow the terminology in the IUPAC Compendium of Chemical Terminology version 2.15 (International Union of Pure and Applied Chemistry) of Sep. 7, 2009.

[0016] As used herein, the prefix term “fluoro”, when placed as a prefix before a chemical entity name, refers to at least one hydrogen atom of the chemical entity has been replaced by fluorine atom.As used herein, the term “fluorinated olefin” refers to linear, branched, or cyclic fluorinated hydrocarbon structures which comprise at least one unsaturated double bond.As used herein, the term “alkyl” refers to linear, branched, or cyclic hydrocarbon structures and combinations of there. Alkyl does not include aromatic structures. Examples of linear alkyl groups include methyl, ethyl, propyl, butyl, pentyl, and hexyl groups. Branched alkyl groups include for example s-and t-butyl, and isopropyl groups. Examples of cyclic hydrocarbon groups include cyclopropyl, cyclopentyl, cyclohexyl, cyclobutyl, and cyclooctyl groups.As used herein, the term “alkoxy” or “alkoxyl” refers to alkyl groups attached to an oxygen atom by a single bond. The other bond of the oxygen atom is connected to a carbon atom. Examples include methoxy, ethoxy, propoxy, isopropoxy, cyclopropyloxy, and cyclohexyloxy.As used herein, the term “another curing agent different from curing agent B” refers to a curing agent that does not have the same chemical structure as curing agent B.

[0017] As used herein, the term “compound” refers to a composition that is able to be cured, i.e., a curable composition, as well as to a mixture of chemical entities that comprises at least a fluoroelastomer and a curing agent. The mixture of chemical entities has not been cured nor has undergone processing conditions that would cause the curing of the mixture of chemical entities to undergo curing.As used herein, the term “cured” refers to that resultant entity that comprised a fluoroelastomer and which has been exposed to those conditions that caused the fluoroelastomer molecules to form sufficient crosslinks among themselves (that is, curing conditions) such that the resultant entity takes on a form or shape orconfiguration or structure that cannot be reprocessed, molded, or extruded into a different one. That is, once a resultant entity which comprised a fluoroelastomer has been exposed to curing conditions to thereby be cured, that entity cannot be re-cured to take on a substantially different form or shape or configuration or structure.

[0018] As used herein, the terms “curing”, “cured” refer to that processing of a compound, also called herein curable composition, which results in an entity taking on a form or shape or configuration or structure that cannot be reprocessed, molded, or extruded into a different one. Such processing refers to the “curing process / processing”, which requires compounds to be exposed to certain conditions in order to initiate the curing process, such conditions called curing conditions.

[0019] The resultant entity of the curing process is a “cured” entity, that is, an article as defined hereinabove. To be clear, curing results in compounds taking on a form or shape or configuration or structure of an article. Cured articles of compounds described herein include, but are not limited to, O-rings, seals, and gaskets.The terms “curing”, “cured” also expressly include differing degrees of processing of a compound such that the resultant entity takes on a form or shape or configuration or structure that cannot be reprocessed, molded, or extruded into a different one and which may exhibit certain physical properties as a result of the curing.

[0020] To the point, these compounds may be initially cured to achieve a non- reprocessable form, shape, etc., which has been termed “cured” herein. The cured compounds may be further subjected to additional curing conditions, which provide additional, subsequent curing. Such additional curing conditions may be variously termed herein either as “curing” or as “post-curing”. That is, the terms “curing”, “cured” refer to both an initial curing process that results in a first cured, resultant entity and also expressly refer to any subsequent curing process that results in a subsequently cured, resultant entity that may or not possess different material or physical properties than those of the first cured, resultant entity.

[0021] Ranges and Preferred VariantsAny range set forth herein expressly includes its endpoints unless explicitly stated otherwise. Setting forth an amount, concentration, or other value or parameter as a range specifically discloses all possible ranges formed from any possible upper range limit and any possible lower range limit, regardless of whether such pairs of upper and lowerrange limits are expressly disclosed herein. Compounds, processes and articles described herein are not limited to specific values disclosed in defining a range in the description.

[0022] The disclosure herein of any variation in terms of materials, chemical entities, methods, steps, values, and / or ranges, etc. — whether identified as preferred or not — of the processes, compounds and articles described herein specifically intends to include any possible combination of materials, methods, steps, values, ranges, etc. For the purpose of providing photographic and sufficient support for the claims, any disclosed combination is a preferred variant of the processes, compounds, and articles described herein.

[0023] CompoundsA) Fluoroelastomers Fluoroelastomers (FKM) typically are copolymers containing 25 to 75 wt %, based on total weight of the fluoroelastomer, of copolymerized units of a first fluoromonomer which may be vinylidene fluoride (VDF) or tetrafluoroehylene (TFE). The remaining units in the fluoroelastomers are comprised of one or more additional copolymerized monomers, different from the first monomer, selected from the group consisting of fluoromonomers, hydrocarbon olefins and mixtures thereof. Examples of such copolymerized monomers include; perfluoromethylvinylether (PMVE), ethylene (E), propylene (P), and hexafluoropropylene (HFP). The hydrogen content of fluoroelastomers (FKM) is at least 0.75 wt%, based on total weight of fluorocarbon elastomer.

[0024] Fluoroelastomers may also, optionally, comprise units of one or more cure site monomers. When present, copolymerized cure site monomers are typically at a level of 0.05 to 7 wt%, based on total weight of fluoroelastomer. Examples of suitable cure site monomers include: i) bromine-, iodine-, or chlorine- containing fluorinated olefins or fluorinated vinyl ethers; ii) nitrile group-containing fluorinated olefins or fluorinated vinyl ethers; and iii) non- conjugated dienes. Fluoroelastomers can be polymerized in the presence of iodide-containing or bromine-containing chain transfer agents such as the diodoperfluoroalkane compounds I(CF2)nI, wherein n is 3 to 7, that provide cure site bonded to thermal carbons of the fluoroelastomer.

[0025] Preferred TFE based fluoroelastomer copolymers include; FE / PMVEZE, TFE / Pand TFE / P / VDF. Preferred VDF based fluorocarbon elastomer copolymer include VDF / HFP, VDF / HFP / TFE, and VDF / PMVE / TFE. Any of these elastomer copolymers may further comprise units of cure site monomer and cure sites formed iodine- containing or bromine-containing chain transfer agents.

[0026] Fluoroelastomers (FKM) typically have a glass transition temperature below 25 degrees C and exhibit little or no crystallinity at room temperature and little or no melting temperature.

[0027] (B) Curing agentThe fluoroelastomers employed in the compounds of the present invention are capable of undergoing crosslinking reactions with curing agent.

[0028] The curing agent is an organic peroxide / polyfunctional coagent system. Useful organic peroxides are those which generate free radicals at curing temperatures. A dialkyl peroxide or a bis(dialkyl peroxide) which decomposes at a temperature above 50 °C. is especially preferred. In many cases it is preferred to use a ditertiarybutyl peroxide having a tertiary carbon atom attached to a peroxy oxygen. Among the most useful peroxides of this type are 2,5-dimethyl-2,5-di(tertiarybutylperoxy)hexyne-3 and 2,5-dimethyl-2,5-di(tertiarybutylperoxy)-hexane. Other peroxides can be selected from such compounds as dicumyl peroxide, dibenzoyl peroxide, tertiarybutyl perbenzoate, and di[l,3-dimethyl-3-(t-butylperoxy)butyl]carbonate. When present in the curable compositions of the invention, 1-5 phr peroxide is typically used.

[0029] The polyfunctional coagent employed with an organic peroxide is a polyunsaturated compound that is capable of cooperating with the peroxide to provide a useful cure. These coagents can be added in an amount between 0.1 and 10 phr, preferably between 2-5 phr. The coagent may be one or more of the following compounds: triallyl cyanurate; triallyl isocyanurate (TAIC); poly triallyl isocyanurate, tri(methallyl)isocyanurate; tris(methallyl)isocyanate (TMAIC); tris(diallylamine)-s- triazine; triallyl phosphite; N,N-diallyl acrylamide; hexaallyl phosphoramide;N,N,N',N' -tetraalkyl tetraphthalamide; N,N,N',N' -tetraallyl malonamide; trivinyl isocyanurate; 2,4,6-trivinyl methyltrisiloxane; and tri(5-norbomene-2- methylene)cyanurate. Particularly useful is triallyl isocyanurate (TAIC) and tri(methallyl) isocyanate (TMAIC).

[0030] (C) Carbon blackThe compounds of the invention comprise one or more carbon blacks.One of the carbon blacks of the invention has a statistical thickness surface area (STSA) between 20 and 40 m2 / g, and alternatively, between 25 and 35 m2 / g. STSA is the external surface area which is accessible to rubber, while the total surface measurement (NSA measurement) is the total surface area which includes micropores. STSA can be measured according to ASTM D6556-07.In addition, the iodine adsorption is above 60 g / kg and ideally at least 145 g / kg. Iodide absorption can be measured according to ASTM D1510.

[0031] Furthermore, the carbon blacks of the invention preferably have a DBP Absorption at least 50 cm3 / 100g, and alternatively, at least 74 cm3 / 100g of nitrogen surface area. Nitrogen surface area can be measured according to ASTM D2414B. Furthermore, the pH of the carbon blacks is at least 7, and alternatively, at least 9. pH can be measured according to ASTM D1512.

[0032] This type of carbon black has non-detectable PAH (Poly Aromatic Hydrocarbons), with a detection limit of 5ppb.The carbon black of the invention can be amorphous.

[0033] An example of the carbon blacks which have the properties disclosed above is CarbonNeat 90 available from CarbonNeat 16930 West Catawba Ave., Suite 102, Cornelius, NC 28031.

[0034] The concentration of carbon black (C) in the compounds ranges from 1 to 100 phr, alternatively, from 5 to 60 phr.

[0035] Two or more carbon blacks can be used. When two or more carbon blacks are used, at least one carbon black needs to be the above-mentioned carbon black.

[0036] When using such specific carbon black, the composition shows good mechanical properties and excellent compression set.

[0037] Other ingredientsThe compounds described herein may additionally comprise a metal sulfide as disclosed in U.S. Published Patent No. 2017 / 0022347A. Examples of such metal sulfide includecalcium sulfide, magnesium sulfide, manganese sulfide, iron sulfide, and copper sulfide. The concentration of metal sulfide is generally from about 0.1 to 20 phr, preferably from 1 to 20 phr, more preferably from 5 to 20 phr.

[0038] Additives such as stabilizers, plasticizers, lubricants, fillers, and processing aids typically utilized in compounding can be incorporated into the compounds described herein, provided they have adequate stability for the intended service conditions. In particular, low temperature performance can be enhanced by incorporation of perfluoropoly ethers.

[0039] In addition to, or in combination with carbon blacks, non-carbon black fillers may be present in the compounds described herein. An example of a non-carbon black filler that may be used includes anhydrous silica such as acidic silica or fumed silica. Such silicas are available from Degussa Aktiengesellschaft (Frankfurt, Germany) under the Aerosil® trademark. A particularly useful type is Aerosil® 200 silica. Other suitable silicas include Reolosil® silicas, available from Tokuyama KK (Tokyo, Japan), for example Reolosil® QS13, Reolosil® QS102, and Reolosil® QS30. Silica amounts range from 1 to 25 phr, but preferably no more than 1 to 7 phr.

[0040] Additional types of fillers include micropowders or fluoroadditives. Micropowders are ordinarily partially crystalline polymers. Micropowders include finely divided, easily dispersed plastic fluoropolymers that are solid at the highest temperature utilized in fabrication and curing of the compounds described herein. The term “solid” refers to a plastic fluoropolymer that has a crystalline melting temperature above the processing temperature(s) of the compounds described herein.

[0041] Micropowders that can be used in these compounds include, but are not limited to, micropowders based on the group of polymers known as tetrafluoroethylene (TFE) polymers. This group includes polytetrafluoroethylene (PTFE) and copolymers of TFE with small concentrations of about 1 mole percent or less of at least one copolymerizable modifying monomer such that the micropowders do not melt or soften during processing of fluoroelastomer A that comprise the micropowders. The modifying monomer may be, for example, hexafluoropropylene (HFP), perfluoro(propyl vinyl) ether (PPVE), perfluorobutyl ethylene, chlorotrifluoroethylene, or another monomer that introduces side groups into the polymer molecule.

[0042] Tetrafluoroethylene polymers used as additives in these compounds includecopolymers of TFE having sufficient concentrations of copolymerized units of one or more monomers to reduce the melting point below that of PTFE. Such copolymers generally have melt viscosity in the range of 0.5-60* 103Pa- s, but viscosities outside this range are also known. Perfluoroolefins and perfluoro(alkyl vinyl) ethers are preferred comonomers. Hexafluoropropylene and perfluoro(propyl vinyl) ether are most preferred. Examples of TFE copolymers include TFE / hexafluoropropylene copolymer and TFE / perfluoro(propyl vinyl)ether copolymers, provided they satisfy constraints on melting temperature with respect to fluoroelastomer processing temperature. These copolymers can be utilized in powder form as isolated from the polymerization medium, if particle size is acceptable, or they can be ground to suitable particle size starting with stock of larger dimensions.

[0043] The amount of non-carbon black filler in these compounds ranges from about 0.01 to 50 phr, alternatively from 0.1 to 20 phr, alternatively at least about 1 to 5 phr.

[0044] Process for preparing the compounds and curing articlesThe compounds described herein may be prepared by mixing until homogeneous fluoroelastomer(s) (A), curing agent(s) (B), carbon black(s) (C), and optional components using rubber compounding procedures such as a two-roll rubber mill, an internal mixer, or in an extruder. These compounds may be cured by the application of heat and / or of pressure sufficient to cause curing agent B to form crosslinks with cure site or a dual cure system may also be used. When compression molding is used to cure, a press cure cycle is preferably followed by a post cure cycle to achieve optimal state of cure during which the press cured compound is heated at elevated temperatures in excess of 200° C. for several hours.

[0045] When cured, the compounds described herein become articles described herein and exhibit suitable thermal stability and chemical resistance for the applications in which these articles are used. These articles are useful: as seals and gaskets for high temperature contexts, in a wide range of chemical environments, in seals for high temperature automotive uses, and O-rings.

[0046] The compounds of the present invention are useful in production of gaskets, tubing, seals and other molded components. Such articles are generally produced bymolding a compounded formulation of the curable composition with various additives under pressure, curing the part, and then subjecting it to a post cure cycle. The cured compositions have excellent mechanical properties as well as excellent thermal stability and chemical resistance.EXAMPLES

[0047] Cure CharacteristicsUnless otherwise noted, cure characteristics were measured using a Montech D-RPA 3000 under the following conditions (ISO 6502):Moving die frequency: 1.66 HzHertz Oscillation amplitude: ±0.5°[deg.]Temperature: 160°C.Sample weight: 6 to 10 gDuration: 45 minutesThe following cure parameters were recorded:MH: maximum torque level, in units of dN.mML: minimum torque level, in units of dN.m ts2: minutes to a 2.26 dNm rise above ML tc90: minutes to 90% of maximum torque Physical Properties

[0048] Physical PropertiesCompression set was performed on plied pips according to ISO 815

[0049] Raw materialsFluoroelastomer A: Tecnoflon® PL 855, is a peroxide curable grade containing vinylidene fluoride (VDF), tetrafluoroethylene (TFE) and, perfluoroalkyl vinyl ether (PAVE), fluorine content is 64%, available from Solvay.Fluoroelastomer B: Viton™ GBL-200S, is a peroxide curable grade containing hexafluoropropylene (HFP), vinylidene fluoride (VDF) and tetrafluoroethylene (TFE), fluorine content is 68%, available from Chemours.Carbon black A: Neat90, STSA is 28-30, available from CarbonNeat 16930 West Catawba Ave., Suite 102, Cornelius, NC 28031Carbon black B: Thermax N990, STSA is 6 to 9, available from Cancarb Limited. Curing agent: Luperox® 101 XL 45, available from (Arkema), it is a curing agent package, including 2,5-DIMETHYL-2,5-DI-(TERT-BUTYLPEROXY)HEXANE, and mineral carriers(CaCO3) and (SiCh).Coagent A TAIC: TAIC DLC®-A 72%, available from Harwick Standard Distribution Corporation, Akron, Ohio, USA.Coagent B: TMAIC, DIAK 8, available from Vanderbilt Chemicals, LLC

[0050] Examples 1 to 8Compounds disclosed in Tables 1 and 2 were prepared.

[0051] Table 1

[0052] Table 2

[0053] Curable composition (Examples 1-8) containing ingredients shown in Table 1 or 2 were made by compounding these ingredients in a conventional manner using an internal mixer and / or a two-roll rubber mill. The properties are also shown in Table 1 and 2.

[0054] Compression set for the composition comprising Carbon black A is improved compare with the composition comprising Carbon black B.The formulation using typically commercially available carbon black such as Thermax N990 and cured using TMAIC coagent do exhibit very low state of cure as indicated by the high compression set.

[0055] While composition using TMAIC coagent and the Neat90 carbon black exhibit compression set value similar to the compression set values obtained using Thermax N990 and TAIC coagent which are known to be used in the market.

Claims

CLAIMSWhat is claimed is:

1. A compound comprising:(A) at least one fluoroelastomer in which the hydrogen content is 0.75 wt% or more,(B) at least a curing agent comprising an organic peroxide and polyfunctional coagent, and(C) one or more carbon blacks, at least one of the carbon blacks has between 20 and 40 m2 / g of statistical thickness surface area.

2. The compound of claim 1, wherein the carbon black has at least 60 g / kg of iodide absorption measured according to ASTM DI 510.

3. The compound of claims 1 or 3, wherein the carbon black comprises two or more kinds of carbon black.

4. The compound of claim 3, wherein the fluoroelastomer further comprises at least one cure site monomer.

5. The compound any one of claims 1 to 4, further comprising at least one ingredient selected from the group comprising micropowders, stabilizers, plasticizers, lubricants, processing aids, and mixtures of these.

6. An article made by curing the composition of any one of the claims 1 to 5.

7. The article of claim 6, in the form of a molded article selected from gasket, tube, seal, diaphragm, sheet, or O-ring.

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