Fluoroelastomer compounds

Abstract

Fluoroelastomer compounds containing a particular type of carbon black are disclosed, along with cured articles formed from these compounds. These compounds show numerous characteristics useful for cured fluoroelastomer articles.

Description

[0001] Cross - Reference to Related Applications

[0002] This application claims the benefit of U.S. Provisional Application No. 63 / 384,691, filed on November 22, 2022, the disclosure of which is hereby incorporated herein by reference in its entirety. Technical Field

[0003] The present invention relates to fluorocarbon elastomer blends containing a specific type of carbon black, and cured articles formed from these blends. Background Art

[0004] Fluorocarbon elastomer (FKM or FPM) articles are characterized by high temperature resistance, acid and alkali resistance, oil resistance, and chemical resistance. The properties of FKM articles are mainly due to the stability and inertness of the comonomers that make up the main part of the polymer backbone of these blends. Such monomers include tetrafluoroethylene (TFE) and vinylidene fluoride (VDF). To fully develop elastomeric properties, the elastomer blends are typically cross - linked (i.e., vulcanized or cured). For this purpose, a small percentage of cure site monomers are optionally copolymerized with these monomers. Upon cross - linking, the cure site monomers react with a curing agent to form a cross - linked elastomeric entity in the form of an article.

[0005] For the use of fluorocarbon elastomer articles in various industries, mechanical properties such as low compression set are also required. The mechanical properties of the cured elastomer blends are typically adjusted by incorporating additives. Carbon black is used as an additive to improve mechanical properties. U.S. Patent No. 10,472,494 (which is hereby incorporated herein by reference in its entirety) discloses fluorocarbon elastomer blends containing a specific type of curing agent and carbon black having an average particle size of at least about 100 nm to about 500 nm.

[0006] The final properties of the finished article can also depend on the type of curing agent selected. Therefore, it is necessary to select an appropriate curing agent that will allow good processing and allow the achievement of good mechanical properties. Summary of the Invention

[0007] Fluorocarbon elastomer blends containing a specific type of carbon black exhibit many properties useful for cured fluorocarbon elastomer articles.

[0008] The present invention relates to a blend comprising:

[0009] (A) a fluorocarbon elastomer having a hydrogen content of at least 0.75 wt% or higher,

[0010] (B) a curing agent comprising an organic peroxide and a polyfunctional co - agent, and

[0011] (C) one or more carbon blacks, at least one of which has a statistical thickness surface area between 20 and 40 m 2 / g.

[0012] The present invention further relates to an article produced using the blend disclosed above. Detailed Description

[0013] Abbreviations

[0014] The claims and the specification herein are to be interpreted using the abbreviations and definitions listed below.

[0015] "h", "hrs" mean hour.

[0016] "%" means the term percent.

[0017] "mol%" means mole percent.

[0018] "wt%" means weight percent.

[0019] "°C" means degree Celsius.

[0020] "parts" means parts by weight.

[0021] "phr" means parts per hundred parts of fluoroelastomer (rubber); this measurement term is used and recognized by those skilled in the art. For example, 3 parts of a component per 100 parts of fluoroelastomer is written as 3 phr. In the blends, methods, and articles described herein, phr is based on 100 parts of fluoroelastomer.

[0022] "g" means gram.

[0023] Definitions

[0024] As used herein, the article "a" means one as well as more than one and does not necessarily limit the noun it refers to to the singular grammatical category.

[0025] As used herein, when used to modify a quantity or value, the terms "about" and "at or about" mean a quantity or value that is an approximation greater than or less than the exact quantity or exact value recited in the claim or described herein. The exact value of the approximation is determined based on what those skilled in the art would recognize as a suitable approximation of that exact value. As used herein, this term indicates that similar values not recited exactly in the claim or not described exactly herein can result in the same results or effects as those values recited in the claim or described herein, for which those skilled in the art will recognize that these similar values acceptably cause.

[0026] 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 the article is unfinished, the term "article" can refer to any item, thing, object, element, device, etc. having a form, shape, or configuration that can undergo further processing to become a finished article. When the article is unfinished, the term "preform" can refer to that form, shape, or configuration, any part of which can undergo further processing to become finished. As used herein, when the article is finished, the term "article" refers to an item, thing, object, element, device, etc. in a form, shape, or configuration suitable for a particular use / purpose without further processing of the entire entity or a part thereof.

[0027] An article can include one or more components or sub-assemblies that are partially finished and awaiting further processing or assembly with other components / sub-assemblies that will together constitute the finished article. Additionally, as used herein, the term "article" can refer to a system or configuration of articles.

[0028] As used herein, the terms "comprises", "comprising", "includes", "including", "has", "having", or any other variations thereof refer to non-exclusive inclusion. For example, a process, method, article, or apparatus that includes a list of elements is not limited to the listed elements, but may include other elements not expressly listed or inherent thereto. Further, unless expressly stated to the contrary, "or" refers to inclusive "or" rather than exclusive "or". For example, the condition A or B is satisfied by any one of the following: A is true (or present) and B is false (or absent), A is false (or absent) 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 variations thereof can refer to non-exclusive inclusion or exclusive inclusion.

[0029] When these terms refer to more exclusive inclusion, these terms limit the scope of the claim to those materials or steps that substantially affect the novel elements of the invention.

[0030] When these terms refer to an exclusive inclusion, these terms exclude any element, step, or component not expressly recited in the claim. As used herein, terms describing a molecule or polymer follow the terms in the IUPAC Compendium of Chemical Terminology_ Version 2.15 (International Union of Pure and Applied Chemistry) of September 7, 2009.

[0031] As used herein, the prefix term "fluoro-", when placed as a prefix before the name of a chemical entity, means that at least one hydrogen atom of the chemical entity has been replaced by a fluorine atom.

[0032] As used herein, the term "fluorinated olefin" means a straight-chain, branched-chain, or cyclic fluorinated hydrocarbon structure containing at least one unsaturated double bond.

[0033] As used herein, the term "alkyl" means a straight-chain, branched-chain, or cyclic hydrocarbon structure and combinations thereof. Alkyl does not include aromatic structures. Examples of straight-chain alkyls include methyl, ethyl, propyl, butyl, pentyl, and hexyl. Branched-chain alkyls include, for example, sec-butyl and tert-butyl, and isopropyl. Examples of cyclic hydrocarbon groups include cyclopropyl, cyclopentyl, cyclohexyl, cyclobutyl, and cyclooctyl.

[0034] As used herein, the term "alkoxy" or "alkoxyl" means an alkyl 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, cyclopropoxy, and cyclohexoxy.

[0035] As used herein, the term "another curing agent different from curing agent B" means a curing agent that does not have the same chemical structure as curing agent B.

[0036] As used herein, the term "blend" means a composition that can be cured (i.e., a curable composition), and refers to a mixture of chemical entities that at least includes a fluoroelastomer and a curing agent. The mixture of chemical entities has not been cured or has not undergone processing conditions that would cause the mixture of chemical entities to cure to undergo curing.

[0037] As used herein, the term "cured" means the resulting entity that includes a fluoroelastomer and has been exposed to those conditions (i.e., curing conditions) that cause sufficient cross-linking to form among the fluoroelastomer molecules themselves, such that the resulting entity assumes a form or shape or configuration or structure that cannot be reprocessed, molded, or extruded into a different form or shape or configuration or structure. That is, once the resulting entity that includes a fluoroelastomer has been exposed to curing conditions and thus cured, the entity cannot be recured to assume a substantially different form or shape or configuration or structure.

[0038] As used herein, the terms "curing" and "cured" refer to the processing of a blend (also referred to herein as a curable composition) that results in an entity having a form, shape, configuration, or structure that cannot be reprocessed, molded, or extruded into a different form, shape, configuration, or structure. Such processing refers to the "curing process", which requires the blend to be exposed to certain conditions to initiate the curing process, such conditions being referred to as curing conditions.

[0039] The entity resulting from the curing process is a "cured" entity, i.e., an article as defined above. It is to be understood that curing results in a blend having the form, shape, configuration, or structure of an article. Cured articles of the blends described herein include, but are not limited to, O-rings, seals, and gaskets.

[0040] The terms "curing" and "cured" also expressly include different degrees of processing of the blend such that the resulting entity has a form, shape, configuration, or structure that cannot be reprocessed, molded, or extruded into a different form, shape, configuration, or structure and the resulting entity as a result of curing may exhibit certain physical properties.

[0041] In this regard, these blends can initially be cured to achieve a non-reprocessable form, shape, etc., which has been referred to herein as "cured". The cured blend can further be subjected to additional curing conditions that provide additional subsequent curing. Such additional curing conditions may be referred to differently herein as "curing" or "post-curing". That is, the terms "curing" and "cured" both refer to the initial curing process that results in the resulting entity of the first cure and also expressly refer to any subsequent curing process that results in a resulting entity of a subsequent cure that may or may not have different materials or physical properties from those of the resulting entity of the first cure.

[0042] Ranges and Preferred Variants

[0043] Unless otherwise expressly stated, any range set forth herein expressly includes its endpoints. Quantities, concentrations, or other values or parameters set forth as a range specifically disclose all possible ranges formed from any possible upper range limit and any possible lower range limit, regardless of whether such pairs of upper and lower range limits are expressly disclosed herein. The blends, methods, and articles described herein are not limited to the specific values disclosed when defining ranges in the specification.

[0044] The disclosure herein of any variations of the methods, blends, and articles described herein, in terms of materials, chemical entities, methods, steps, values, and / or ranges, etc. (whether or not identified as preferred), is specifically intended to include any possible combinations of materials, methods, steps, values, ranges, etc. For the purpose of providing detailed, accurate, and sufficient support for the claims, any disclosed combination is a preferred variation of the methods, blends, and articles described herein.

[0045] Blend

[0046] A) Fluoroelastomer

[0047] Fluoroelastomers (FKM) are typically copolymers containing copolymer units of a first fluoromonomer in an amount of 25 to 75 wt% based on the total weight of the fluoroelastomer. The first fluoromonomer can be vinylidene fluoride (VDF) or tetrafluoroethylene (TFE). The remaining units in the fluoroelastomer are constituted by one or more additional comonomers that are different from the first monomer and are selected from the group consisting of fluoromonomers, hydrocarbon olefins, and mixtures thereof. Examples of such comonomers include: perfluoromethyl vinyl ether (PMVE), ethylene (E), propylene (P), and hexafluoropropylene (HFP). The hydrogen content of the fluoroelastomer (FKM) is at least 0.75 wt% based on the total weight of the fluorocarbon elastomer.

[0048] The fluoroelastomer may also optionally contain units of one or more cure site monomers. When present, the copolymerized cure site monomers are typically at a level of 0.05 to 7 wt% based on the total weight of the fluoroelastomer. Examples of suitable cure site monomers include: i) fluorinated olefins or fluorinated vinyl ethers containing bromine, iodine, or chlorine; ii) fluorinated olefins or fluorinated vinyl ethers containing a nitrile group; and iii) non-conjugated dienes. The fluoroelastomer can be polymerized in the presence of an iodine- or bromine-containing chain transfer agent (such as diiodoperfluoroalkane compounds I(CF2) n I, where n is from 3 to 7) that provides a cure site with a thermal carbon bond to the fluoroelastomer.

[0049] Preferred TFE-based fluoroelastomer copolymers include: FE / PMVE / E, TFE / P, and TFE / P / VDF. Preferred VDF-based fluorocarbon elastomer copolymers include VDF / HFP, VDF / HFP / TFE, and VDF / PMVE / TFE. Any of these elastomer copolymers can further contain units of cure site monomers and an iodine- or bromine-containing chain transfer agent that forms a cure site.

[0050] Fluoroelastomers (FKM) typically have a glass transition temperature below 25 °C and exhibit little or no crystallinity and little or no melting temperature at room temperature.

[0051] (B) Curing agent

[0052] The fluoroelastomer used in the blend of the present invention is capable of undergoing a crosslinking reaction with a curing agent.

[0053] The curing agent is an organic peroxide / polyfunctional coagent system. Useful organic peroxides are those that generate free radicals at the curing temperature. Dialkyl peroxides or bis(dialkyl peroxides) that decompose at temperatures above 50 °C are particularly preferred. In many cases, di-tert-butyl peroxide having a tertiary carbon atom attached to the peroxy oxygen is preferably used. Among them, the most useful peroxides of this type are 2,5-dimethyl-2,5-di(tert-butylperoxy)hex-3-yne and 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane. Other peroxides can be selected from compounds such as dicumyl peroxide, benzoyl peroxide, tert-butyl perbenzoate, and bis[1,3-dimethyl-3-(tert-butylperoxy)butyl] carbonate. When present in the curable composition of the present invention, typically 1-5 phr of peroxide is used.

[0054] The polyfunctional coagent employed with the organic peroxide is a polyunsaturated compound capable of cooperating with the peroxide to provide useful curing. These coagents can be added in amounts between 0.1 and 10 phr, preferably between 2 and 5 phr. The coagent can be one or more of the following compounds: triallyl cyanurate; triallyl isocyanurate (TAIC); poly(triallyl isocyanurate), tris(methallyl) isocyanurate; tris(methallyl) isocyanate (TMAIC); tris(diallylamino)-s-triazine; triallyl phosphite; N,N-diallylacrylamide; hexallyl phosphoramide; N,N,N',N'-tetraalkyltetraphthalamide; N,N,N',N'-tetraallylmalonamide; trivinyl isocyanurate; 2,4,6-trivinylmethyltrisiloxane; and tris(5-norbornene-2-methylene) cyanurate. Particularly useful are triallyl isocyanurate (TAIC) and tris(methallyl) isocyanate (TMAIC).

[0055] (C) Carbon black

[0056] The blend of the present invention contains one or more carbon blacks.

[0057] One of the carbon blacks of the present invention has a statistical thickness surface area (STSA) between 20 and 40 m 2 / g, and alternatively between 25 and 35 m 2 / g. The STSA is the outer surface area accessible to the rubber, while the total surface measurement (NSA measurement) is the total surface area including micropores. The STSA can be measured according to ASTM D6556-07.

[0058] In addition, the iodine adsorption rate is higher than 60 g / kg and desirably at least 145 g / kg. The iodide absorption rate can be measured according to ASTM D1510.

[0059] In addition, the carbon black of the present invention preferably has at least 50 cm 3 / 100 g, and alternatively at least 74 cm 3 / 100 g of DBP absorption rate of nitrogen surface area. The nitrogen surface area can be measured according to ASTM D2414B.

[0060] In addition, the pH of the carbon black is at least 7, and alternatively at least 9.

[0061] The pH can be measured according to ASTM D1512.

[0062] This type of carbon black has undetectable PAH (polycyclic aromatic hydrocarbons), with a detection limit of 5 ppb.

[0063] The carbon black of the present invention can be amorphous.

[0064] An example of carbon black having the properties disclosed above is CarbonNeat 90 available from CarbonNeat, Inc., Room 102, 16930 West Catawba Avenue, Cornelius, NC 28031.

[0065] The concentration of carbon black (C) in the blend ranges from 1 to 100 phr, alternatively 5 to 60 phr.

[0066] Two or more types of carbon black can be used. When two or more types of carbon black are used, at least one type of carbon black needs to be the above-mentioned carbon black.

[0067] When using this specific carbon black, the composition shows good mechanical properties and excellent compression set.

[0068] Other ingredients

[0069] The blends described herein can additionally contain metal sulfides as disclosed in U.S. Published Patent No. 2017 / 0022347A. Examples of such metal sulfides include calcium sulfide, magnesium sulfide, manganese sulfide, iron sulfide, and copper sulfide. The concentration of the metal sulfide is generally about 0.1 to 20 phr, preferably 1 to 20 phr, more preferably 5 to 20 phr.

[0070] Additives typically used in compounding such as stabilizers, plasticizers, lubricants, fillers, and processing aids can be incorporated into the blends described herein provided they have sufficient stability for the intended use conditions. In particular, the low-temperature performance can be enhanced by incorporating perfluoropolyether.

[0071] In addition to or in combination with carbon black, non-carbon black fillers may be present in the blends described herein. Examples of non-carbon black fillers that may be used include anhydrous silica, such as acidic silica or fumed silica. Such silica is available from Degussa Aktiengesellschaft (Frankfurt, Germany) under a trade name. A particularly useful type is 200 silica. Other suitable silicas include those available from Tokuyama KK (Tokyo, Japan), such as silica, e.g., QS13, QS102, and QS30. The amount of silica ranges from 1 to 25 phr, but preferably does not exceed 1 to 7 phr.

[0072] Additional types of fillers include fine powders or fluorine additives. Fine powders are generally partially crystalline polymers. Fine powders include finely divided, readily dispersible plastic fluoropolymers that are solid at the highest temperatures used in the manufacture and curing of the blends described herein. The term "solid" refers to a plastic fluoropolymer having a crystalline melting temperature higher than the processing temperature of the blends described herein.

[0073] Fine powders that may be used in these blends include, but are not limited to, fine powders based on polymers of the group known as tetrafluoroethylene (TFE) polymers. This group includes polytetrafluoroethylene (PTFE) and copolymers of TFE with a small concentration of at least one copolymerizable modifying monomer of about 1 mole percent or less such that the fine powder does not melt or soften during the processing of the fluoroelastomer A containing the fine powder. The modifying monomer may be, for example, hexafluoropropylene (HFP), perfluoro(propyl vinyl) ether (PPVE), perfluorobutylethylene, chlorotrifluoroethylene, or another monomer that introduces a side group into the polymer molecule.

[0074] Tetrafluoroethylene polymers used as additives in these blends include copolymers of TFE having a sufficient concentration of copolymer units of one or more monomers to reduce the melting point to below that of PTFE. Such copolymers generally have a melt index in the range of 0.5 - 60×10 3The melt viscosity is within the range of Pa·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 copolymers and TFE / perfluoro(propyl vinyl) ether copolymers, provided that they meet the limitation of the melting temperature relative to the processing temperature of the fluoroelastomer. If the particle size is acceptable, then these copolymers can be used in the form of a powder separated from the polymerization medium, or they can be ground to a suitable particle size starting from a larger size feedstock.

[0075] In these blends, the amount of non-carbon black filler ranges from about 0.01 to 50 phr, alternatively 0.1 to 20 phr, alternatively at least about 1 to 5 phr.

[0076] Methods for preparing blends and cured articles

[0077] The blends described herein can be prepared by mixing one or more fluoroelastomers (A), one or more curing agents (B), one or more carbon blacks (C), and optional components using a rubber compounding procedure such as a two-roll rubber mill, an internal mixer, or in an extruder until homogeneous. These blends can be cured by applying heat and / or pressure sufficient to cause the curing agent B to form crosslinks with the curing sites, or a dual-curing system can also be used. When compression molding is used for curing, the pressure-curing cycle is preferably followed by a post-curing cycle to achieve an optimal cured state, during which the pressure-cured blend is heated at a high temperature above 200 °C for several hours.

[0078] When cured, the blends described herein become the 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 environments, in a wide range of chemical environments, in seals for high-temperature automotive applications, and as O-rings.

[0079] The blends of the present invention are useful in the production of gaskets, tubing, seals, and other molded parts. Such articles are typically produced by molding a curable composition admixed with various additives under pressure, curing the part, and then subjecting it to a post-curing cycle. The cured composition has excellent mechanical properties as well as excellent thermal stability and chemical resistance.

[0080] Examples

[0081] Curing characteristics

[0082] Unless otherwise specified, the curing characteristics are measured using a Montech D-RPA 3000 under the following conditions (ISO 6502):

[0083] Moving die head frequency: 1.66 Hz

[0084] Hertz oscillation amplitude: ±0.5° [degrees]

[0085] Temperature: 160 °C

[0086] Sample weight: 6 to 10 g

[0087] Duration: 45 minutes

[0088] Record the following curing parameters:

[0089] MH: Maximum torque level, in dN.m

[0090] ML: Minimum torque level, in dN.m

[0091] ts2: Minutes to rise 2.26 dNm from ML

[0092] tc90: Minutes to reach 90% of the maximum torque Physical properties

[0093] Physical properties

[0094] Compression set on laminated tubing according to ISO 815

[0095] Raw materials

[0096] Fluoroelastomer A: PL 855, a peroxide-curable grade, contains vinylidene fluoride (VDF), tetrafluoroethylene (TFE) and perfluoroalkyl vinyl ether (PAVE), with a fluorine content of 64%, available from Solvay

[0097] Fluoroelastomer B: Viton TM GBL-200S, a peroxide-curable grade, contains hexafluoropropylene (HFP), vinylidene fluoride (VDF) and tetrafluoroethylene (TFE), with a fluorine content of 68%, available from Chemours

[0098] Carbon black A: Neat90, STSA is 28 - 30, available from CarbonNeat, 16930 West Catawba Avenue, Suite 102, Cornelius, NC 28031

[0099] Carbon black B: Thermax N990, STSA is 6 - 9, available from Cancarb Limited

[0100] Curing agent: 101XL 45, available from (Arkema), is a curing agent formulation package that includes 2,5 - dimethyl - 2,5 - di - (tert - butylperoxy)hexane, and mineral carriers (CaCO3) and mineral carriers (SiO2).

[0101] Additive A TAIC: TAIC 72%, available from Harwick Standard Distribution Corporation, Akron, Ohio, USA.

[0102] Additive B: TMAIC, DIAK 8, available from Vanderbilt Chemicals, LLC

[0103] Examples 1 to 8

[0104] Prepare the blends disclosed in Tables 1 and 2.

[0105] Table 1

[0106]

[0107] Table 2

[0108]

[0109] The curable compositions (Examples 1 - 8) containing the components shown in Table 1 or 2 are prepared by compounding these components in a conventional manner using a Banbury mixer and / or a two - roll rubber mill. The properties are also shown in Tables 1 and 2.

[0110] Compared with the composition containing Carbon Black B, the compression set of the composition containing Carbon Black A is improved.

[0111] Formulations using typically commercially available carbon blacks such as Thermax N990 and cured using the TMAIC additive do exhibit a very low cure state, as indicated by a high compression set.

[0112] While the composition using the TMAIC additive and Neat90 carbon black exhibits a compression set value similar to the compression set value obtained using Thermax N990 and the TAIC additive known to be used in the market.

Claims

1. A blend comprising: (A) at least one fluoroelastomer having a hydrogen content of 0.75 wt% or higher, (B) at least one curing agent comprising an organic peroxide and a polyfunctional coagent, and (C) one or more carbon blacks, at least one of said carbon blacks having a statistical thickness surface area between 20 and 40 m 2 / g.

2. The admixture according to claim 1, wherein The carbon black has an iodine absorption rate of at least 60 g / kg as measured according to ASTM D1510.

3. The admixture according to claim 1 or 3, wherein The carbon black comprises two or more types of carbon black.

4. The admixture according to claim 3, wherein, The fluoroelastomer further comprises at least one curing site monomer.

5. The blend according to any one of claims 1 to 4, further comprising at least one component selected from the group consisting of: fine powder, stabilizer, plasticizer, lubricant, processing aid, and mixtures thereof.

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

7. The article according to claim 6, wherein the article is in the form of a molded article selected from the group consisting of gaskets, tubes, seals, spacers, sheets, or O-rings.

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