CURABLE FLUOROELASTOMER COMPOSITIONS AND LOW FRICTION CURED FLUOROELASTOMERS FORMED THEREFROM (fkM)

Abstract

A curable fluoroelastomer composition comprises a curable fluoroelastomer, a dehydrohalogenating agent, an acid acceptor comprising bismuth oxide present in the curable fluoroelastomer composition in an amount of at least 3 parts per hundred parts by weight of the curable fluoroelastomer, and at least one silicon-containing chemical present in the curable fluoroelastomer composition in an amount of at least 0.2 parts per hundred parts by weight of the curable fluoroelastomer. A cured fluoroelastomer cured from the curable fluoroelastomer composition has a static coefficient of friction and a dynamic coefficient of friction of less than 1.

Description

[0001] Cross - Reference to Related Applications

[0002] This application claims the benefit of priority of U.S. Provisional Patent Application No. 63 / 415,436, filed on October 12, 2022, the disclosure of which is hereby incorporated by reference in its entirety. Technical Field

[0003] This disclosure relates to compositions and methods for curing fluorinated elastomers and cured fluorinated elastomers. More specifically, this disclosure relates to curable fluorinated elastomer compositions that comprise a curable fluorinated elastomer, a dehydrohalogenating agent, an acid acceptor comprising bismuth oxide, and at least one silicone - containing chemical. Background Art

[0004] Low - friction fluorinated elastomer materials are desirable for many applications.

[0005] In automotive shaft seals, high friction between the fluorinated elastomer shaft seal and the rotating shaft results in energy loss in internal combustion engines, and low surface friction of the shaft seal has been sought to improve fuel efficiency.

[0006] In electric vehicle systems, high rotational speeds of the motor shaft generate excessive frictional heat on the sealing material, and reduction of surface friction is considered important for minimizing heat generation and enabling system design at high motor speeds.

[0007] The application of low - friction coatings is one way to reduce friction between the surfaces of rubber components. However, this requires additional processes and costs, and the durability of the coatings often becomes a problem.

[0008] A better way to achieve low surface friction is through material composition rather than coating application. Summary of the Invention

[0009] The curable fluorinated elastomer compositions disclosed herein provide cured fluorinated elastomers with low friction. Relative to conventional low - friction coating methods, the friction reduction of the fluorinated elastomers can highly contribute to improving energy efficiency and reducing costs.

[0010] In one embodiment, the curable fluorinated elastomer composition comprises a curable fluorinated elastomer, a dehydrohalogenating agent, an acid acceptor comprising bismuth oxide (Bi 2 O 3 ) present in the curable fluorinated elastomer composition in an amount of at least 3 parts per hundred parts by weight of the curable fluorinated elastomer (phr), and at least one silicone - containing chemical present in the curable fluorinated elastomer composition in an amount of at least 0.05 parts per hundred parts by weight of the curable fluorinated elastomer.

[0011] In one embodiment of the composition, bismuth oxide is present in the curable fluorine-containing elastomer composition in an amount of 5 parts per hundred parts by weight to 15 parts per hundred parts by weight of the curable fluorine-containing elastomer.

[0012] In another embodiment of the composition, the at least one silicon-containing chemical is present in the curable fluorine-containing elastomer composition in an amount of 0.05 parts per hundred parts by weight to 5 parts per hundred parts by weight of the curable fluorine-containing elastomer.

[0013] In another embodiment of the composition, the at least one silicon-containing chemical is selected from the group consisting of silica, calcium silicate (Ca 2 SiO 4 ), calcium metasilicate (CaSiO 3 ), silicone, γ-aminopropyltriethoxysilane, vinyltriethoxysilane, and combinations thereof.

[0014] In another embodiment of the composition, the dehydrohalogenating agent is present in the curable fluorine-containing elastomer composition in an amount of at least 1.0 part per hundred parts by weight of the curable fluorine-containing elastomer.

[0015] In another embodiment of the composition, the dehydrohalogenating agent is selected from the group consisting of 2,2-bis(4-hydroxyphenyl)hexafluoropropane, methylhydroquinone, and 2-methylresorcinol.

[0016] In another embodiment of the composition, the curable fluorine-containing elastomer comprises a peroxide-curable fluorine-containing elastomer capable of being cured by a peroxide curing system, and the curable fluorine-containing elastomer composition further comprises a peroxide curing agent.

[0017] In another embodiment of the composition, the curable fluorine-containing elastomer composition contains magnesium oxide and calcium hydroxide in a combined form of less than 0.1 part per hundred parts by weight of the curable fluorine-containing elastomer.

[0018] In another embodiment of the composition, the curable fluorine-containing elastomer composition does not contain or substantially does not contain magnesium oxide and calcium hydroxide.

[0019] In another embodiment of the composition, the curable fluorine-containing elastomer is a dimer of hexafluoropropene and vinylidene fluoride.

[0020] In another embodiment, the cured fluorine-containing elastomer cured from the curable fluorine-containing elastomer composition comprises a curable fluorine-containing elastomer, a dehydrohalogenating agent, and bismuth oxide (Bi 2 O 3) an acid acceptor, and at least one silicon-containing chemical present in the curable fluorine-containing elastomer composition in an amount of at least 0.05 parts per hundred parts by weight of the curable fluorine-containing elastomer.

[0021] In one embodiment of the cured fluorine-containing elastomer, bismuth oxide is present in the curable fluorine-containing elastomer composition in an amount of 5 parts per hundred parts by weight to 15 parts per hundred parts by weight of the curable fluorine-containing elastomer.

[0022] In another embodiment of the cured fluorine-containing elastomer, the at least one silicon-containing chemical is present in the curable fluorine-containing elastomer composition in an amount of 0.05 parts per hundred parts by weight to 5 parts per hundred parts by weight of the curable fluorine-containing elastomer.

[0023] In another embodiment of the cured fluorine-containing elastomer, the at least one silicon-containing chemical is selected from the group consisting of silica, calcium metasilicate (CaSiO 3 ), silicone, γ-aminopropyltriethoxysilane, vinyltriethoxysilane, and combinations thereof.

[0024] In another embodiment of the cured fluorine-containing elastomer, the dehydrohalogenating agent is present in the curable fluorine-containing elastomer composition in an amount of at least 1.0 part per hundred parts by weight of the curable fluorine-containing elastomer.

[0025] In another embodiment of the cured fluorine-containing elastomer, the dehydrohalogenating agent is selected from the group consisting of 2,2-bis(4-hydroxyphenyl)hexafluoropropane, methylhydroquinone, and 2-methylresorcinol.

[0026] In another embodiment of the cured fluorine-containing elastomer, the curable fluorine-containing elastomer comprises a peroxide-curable fluorine-containing elastomer capable of being cured by a peroxide curing system, and the curable fluorine-containing elastomer composition further comprises a peroxide curing agent.

[0027] In another embodiment of the cured fluorine-containing elastomer, the curable fluorine-containing elastomer composition contains less than 0.1 part per hundred parts by weight of the curable fluorine-containing elastomer of magnesium oxide and calcium hydroxide in combination.

[0028] In another embodiment of the cured fluorine-containing elastomer, the cured fluorine-containing elastomer does not contain or substantially does not contain magnesium oxide and calcium hydroxide.

[0029] In another embodiment of the cured fluorine-containing elastomer, the cured fluorine-containing elastomer has a static coefficient of friction less than 0.5.

[0030] In another embodiment of the cured fluorine-containing elastomer, the cured fluorine-containing elastomer has a static coefficient of friction of 0.2 to 0.4.

[0031] In another embodiment of the cured fluorine-containing elastomer, the cured fluorine-containing elastomer has a dynamic coefficient of friction of less than 0.5.

[0032] In another embodiment of the cured fluorine-containing elastomer, the cured fluorine-containing elastomer has a dynamic coefficient of friction of 0.15 to 0.4.

[0033] In another embodiment of the cured fluorine-containing elastomer, the cured fluorine-containing elastomer has a tensile strength of 9.0 MPa to 25 MPa.

[0034] In another embodiment of the cured fluorine-containing elastomer, the cured fluorine-containing elastomer has an elongation at break of 150% to 200%.

[0035] In yet another embodiment, a method of curing a curable fluorine-containing elastomer includes forming a curable fluorine-containing elastomer composition and heating the curable fluorine-containing elastomer composition to a curing temperature to cure the curable fluorine-containing elastomer. The curable fluorine-containing elastomer composition comprises the curable fluorine-containing elastomer, a dehydrohalogenating agent, an acid acceptor comprising bismuth oxide (Bi 2 O 3 ) present in the curable fluorine-containing elastomer composition in an amount of at least 3 parts per hundred parts by weight of the curable fluorine-containing elastomer, and at least one silicon-containing chemical present in the curable fluorine-containing elastomer composition in an amount of at least 0.05 parts per hundred parts by weight of the curable fluorine-containing elastomer.

[0036] In one embodiment of the method, the heating includes pressure curing the curable fluorine-containing elastomer composition, and wherein the curing temperature is in the range of about 160 °C to about 190 °C, and the curing time is in the range of about 5 minutes to about 90 minutes.

[0037] In another embodiment of the method, the method further includes post-curing the cured fluorine-containing elastomer at a post-curing temperature for a post-curing time.

[0038] In another embodiment of the method, the post-curing temperature is in the range of about 200 °C to about 260 °C, and the post-curing time is about 15 minutes or longer.

[0039] In another embodiment of the method, bismuth oxide is present in the curable fluorine-containing elastomer composition in an amount of 5 parts per hundred parts by weight to 15 parts per hundred parts by weight of the curable fluorine-containing elastomer.

[0040] In another embodiment of the method, the at least one silicon-containing chemical is present in the curable fluorine-containing elastomer composition in an amount of 0.05 parts per hundred parts by weight to 5 parts per hundred parts by weight of the curable fluorine-containing elastomer.

[0041] In another embodiment of the method, the at least one silicon-containing chemical is selected from the group consisting of silica, calcium silicate (Ca 2 SiO 4 ), calcium metasilicate (CaSiO 3 ), silicone, γ-aminopropyltriethoxysilane, vinyltriethoxysilane, and combinations thereof.

[0042] In another embodiment of the method, the dehydrohalogenating agent is present in the curable fluorine-containing elastomer composition in an amount of at least 1.0 part per hundred parts by weight of the curable fluorine-containing elastomer.

[0043] In another embodiment of the method, the dehydrohalogenating agent is selected from the group consisting of 2,2-bis(4-hydroxyphenyl)hexafluoropropane, methylhydroquinone, and 2-methylresorcinol.

[0044] In another embodiment of the method, the curable fluorine-containing elastomer comprises a peroxide-curable fluorine-containing elastomer capable of being cured by a peroxide curing system, and the curable fluorine-containing elastomer composition further comprises a peroxide curing agent.

[0045] In another embodiment of the method, the curable fluorine-containing elastomer composition contains less than 0.1 part per hundred parts by weight of the curable fluorine-containing elastomer of magnesium oxide and calcium hydroxide in combination.

[0046] In another embodiment of the method, the cured fluorine-containing elastomer is free or substantially free of magnesium oxide and calcium hydroxide.

[0047] In another embodiment of the method, the cured fluorine-containing elastomer has a static coefficient of friction of less than 0.5.

[0048] In another embodiment of the method, the cured fluorine-containing elastomer has a static coefficient of friction of 0.2 to 0.4.

[0049] In another embodiment of the method, the cured fluorine-containing elastomer has a dynamic coefficient of friction of less than 0.5.

[0050] In another embodiment of the method, the cured fluorine-containing elastomer has a dynamic coefficient of friction of 0.15 to 0.4.

[0051] In combination with the accompanying drawings that illustrate the principles of the invention by way of example, other features and advantages of the invention will be apparent from the following more detailed description of the preferred embodiments. Detailed Description

[0052] Exemplary curable fluorinated elastomer compositions and cured fluorinated elastomers are provided that contain bismuth oxide and at least one silicon-containing chemical.

[0053] In exemplary embodiments, the compositions and methods provide cured fluorinated elastomers with low friction. In exemplary embodiments, the low-friction cured fluorinated elastomers are free or substantially free of strong acid acceptors, which include but are not limited to magnesium oxide, calcium oxide, and calcium hydroxide.

[0054] As used herein, "silicon-containing chemical" or "Si-containing chemical" refers to any compound that contains silicon.

[0055] As used herein, "low-friction cured fluorinated elastomer" refers to a cured fluorinated elastomer having a static coefficient of friction less than 1 and a dynamic coefficient of friction less than 1. In exemplary embodiments, the low-friction cured fluorinated elastomer has a static coefficient of friction of about 0.5 or less and a dynamic coefficient of friction of about 0.5 or less.

[0056] As used herein, "substantially free of strong acid acceptors" refers to a curable fluorinated elastomer composition or a cured fluorinated elastomer formed from a curable fluorinated elastomer composition that has less than 1 part per hundred parts by weight of curable fluorinated elastomer (phr) of strong acid acceptor. Suitable amounts of strong acid acceptor in the curable fluorinated elastomer composition can include but are not limited to less than 1 phr, less than 0.5 phr, less than 0.4 phr, less than 0.3 phr, less than 0.2 phr, less than 0.1 phr, less than 0.05 phr, or any value, range, or sub-range therebetween.

[0057] In exemplary embodiments, the curable fluorinated elastomer composition comprises a curable fluorinated elastomer, a dehydrohalogenating agent, an acid acceptor comprising bismuth oxide (Bi 2 O 3 ) present in the curable fluorinated elastomer composition in an amount of at least 3 phr, and at least one silicon-containing chemical present in the curable fluorinated elastomer composition in an amount of at least 0.05 phr.

[0058] Suitable amounts of bismuth oxide in the curable fluorinated elastomer composition can include but are not limited to 1.5 phr or greater, 2 phr or greater, 3 phr or greater, 1.5 phr to 25 phr, 2 phr to 20 phr, 3 phr to 18 phr, 5 phr to 15 phr, or any value, range, or sub-range therebetween.

[0059] Suitable amounts of the silicon-containing chemical may include, but are not limited to, at least 0.05 phr, at least 0.1 phr, at least 0.2 phr, from 0.05 phr to 15 phr, from 0.1 phr to 15 phr, from 0.2 phr to 5 phr, or any value, range or sub-range therebetween.

[0060] Suitable silicon-containing chemicals may include, but are not limited to, silica; calcium silicate (Ca 2 SiO 4 ); calcium metasilicate (CaSiO 3 ); silicone; γ-aminopropyltriethoxysilane; vinyltriethoxysilane; talc; diatomaceous earth; wollastonite; metal silicates including, but not limited to, calcium silicate, sodium silicate, borosilicate, lithium disilicate and / or potassium silicate; water glass; soda-lime glass; borosilicate glass; Z-glass; E-glass; sintered glass; silica including, but not limited to, fumed silica, pyrogenic silica, precipitated silica and / or silica fume; and / or metallic silicon.

[0061] Suitable amounts of the dehydrohalogenating agent may include, but are not limited to, at least 1.0 phr, from 1.0 phr to 5 phr, at least 1.2 phr, from 1.2 phr to 5 phr, from 1.0 phr to 4 phr, or any value, range or sub-range therebetween.

[0062] Suitable dehydrohalogenating agents may include, but are not limited to, 2,2-bis(4-hydroxyphenyl)hexafluoropropane (BpAF), methylhydroquinone, 2-methylresorcinol, 2,2-bis(4-hydroxyphenyl)propane, 2,2-bis(4-hydroxyphenyl)perfluoropropane, resorcinol, 1,3-dihydroxybenzene, 1,7-dihydroxynaphthalene, 2,7-dihydroxynaphthalene, 1,6-dihydroxynaphthalene, 4,4'-dihydroxybiphenyl, 4,4'-dihydroxystilbene, 2,6-dihydroxyanthracene, hydroquinone, catechol, 2,2-bis(4-hydroxyphenyl)butane, 4,4-bis(4-hydroxyphenyl)valeric acid, 2,2-bis(4-hydroxyphenyl)tetrafluorodichloropropane, 4,4'-dihydroxydiphenyl sulfone, 4,4'-dihydroxydiphenyl ketone, tris(4-hydroxyphenyl)methane, 3,3',5,5'-tetrachlorobisphenol A and / or 3,3',5,5'-tetrabromobisphenol A.

[0063] In some embodiments, the curable fluorinated elastomer comprises a polyhydroxy-curable fluorinated elastomer capable of being cured by a polyhydroxy curing agent. As used herein, "polyhydroxy-curable" refers to a fluorinated elastomer known to crosslink with polyhydroxy curing agents such as BpAF. Such fluorinated elastomers include, but are not limited to, those fluorinated elastomers having multiple carbon-carbon double bonds along the elastomeric polymer backbone and fluorinated elastomers containing sites that can be easily dehydrofluorinated. The latter fluorinated elastomers include, but are not limited to, those fluorinated elastomers containing adjacent copolymer units of vinylidene fluoride (VF2) and hexafluoropropylene (HFP), and fluorinated elastomers containing adjacent copolymer units of VF2 (or tetrafluoroethylene) and a fluorinated comonomer having an acidic hydrogen atom (e.g., 2-hydro-pentafluoropropene; 1-hydro-pentafluoropropene; trifluoroethylene; 2,3,3,3-tetrafluoropropene; or 3,3,3-trifluoropropene). Preferred fluorinated elastomers include copolymers of: i) vinylidene fluoride with hexafluoropropylene and optionally tetrafluoroethylene (TFE); ii) vinylidene fluoride with perfluoro(alkyl vinyl ether) such as perfluoro(methyl vinyl ether), 2-hydro-pentafluoropropene and optionally tetrafluoroethylene; iii) tetrafluoroethylene with propylene and 3,3,3-trifluoropropene; iv) tetrafluoroethylene, perfluoro(methyl vinyl ether) and hexafluoro-2-(pentafluorophenoxy)-1-(trifluorovinyloxy)propane, and v) ethylene with tetrafluoroethylene, perfluoro(methyl vinyl ether) and 3,3,3-trifluoropropene. In some embodiments, the polyhydroxy-curable fluorinated elastomer is a dimer of hexafluoropropylene and vinylidene fluoride. The polyhydroxy-curable fluorinated elastomer may also include an iodine-containing elastomer, a bromine-containing elastomer or a chlorine-containing elastomer. For example, a small amount (0.01 wt% - 1 wt%) of chlorine, bromine or iodine may be introduced together with a telogen (e.g., CH 2 I 2 or I(CF 2 ) 4 I) or a monomer (e.g., CH 2 =CHCF 2 CF 2 X (X = Br, I) or chlorotrifluoroethylene). In some embodiments, the polyhydroxy-curable fluorinated elastomer contains a diolefin, such as, for example, CH 2 =CH(CF 2 ) n CH=CH 2 (where n = 2 - 8) or CF 2 =CFO(CF 2 ) n OCF=CF 2 (where n = 2 - 8).

[0064] In some embodiments, the curable fluorinated elastomer is a dimer of hexafluoropropylene and vinylidene fluoride.

[0065] In some embodiments, the curable fluorinated elastomer comprises a peroxide-curable fluorinated elastomer capable of being cured by a peroxide curing system, and the curable fluorinated elastomer composition further comprises a peroxide curing agent.

[0066] In some embodiments, the curable composition comprises one or more additives. Suitable additives can include, but are not limited to, fillers, processing aids, accelerators, weak acid acceptors, peroxides, and / or colorants.

[0067] The filler can be one or more inorganic fillers, one or more polymeric fillers, or a combination thereof. Suitable inorganic fillers can include, but are not limited to, medium thermal carbon black, silica, talc, titanium dioxide (TiO 2 ), barium sulfate (BaSO 4 ), and / or calcium carbonate (CaCO 3 ). Suitable polymeric fillers can include, but are not limited to, polytetrafluoroethylene (PTFE).

[0068] Suitable amounts of the filler can include, but are not limited to, about 10 phr to about 40 phr, about 20 phr to about 40 phr, about 25 phr to about 35 phr, about 30 phr, or any value, range, or sub-range therebetween.

[0069] Suitable amounts of the processing aid can include, but are not limited to, about 0.1 phr to about 2 phr, about 0.2 phr to about 2 phr, about 0.5 phr to about 1.5 phr, about 1 phr, or any value, range, or sub-range therebetween.

[0070] Suitable accelerators can include, but are not limited to, tertiary sulfonium salts such as [(C 6 H 5 ) 2 S + (C 6 H 13 )][Cl] - and [(C 6 H 13 ) 2 S(C 6 H 5 )] + [CH 3 CO 2 - and quaternary ammonium, phosphonium, arsonium, and stibonium salts of the formula R 5 R 6 R 7 R 8 Y + X - wherein Y is phosphorus, nitrogen, arsenic, or antimony; R 5 、R 6 、R 7 and R​8 each being C 1 -C 20 alkyl, aryl, aralkyl, alkenyl and their chloro-, fluoro-, bromo-, cyano-, -OR and -COOR-substituted analogs, where R is C 1 -C 20 alkyl, aryl, aralkyl, alkenyl, and where X is halide, hydroxide, sulfate, sulfite, carbonate, pentachlorothiophenolate, tetrafluoroborate, hexafluorosilicate, hexafluorophosphate, dimethylphosphate, and C 1 -C 20 alkyl, aryl, aralkyl and alkenyl carboxylates and dicarboxylates. Particular preference is given to benzyltriphenylphosphonium chloride, benzyltriphenylphosphonium bromide, tetrabutylammonium hydrogensulfate, tetrabutylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium bromide, tributylallylphosphonium chloride, tributyl-(2-methoxypropyl)phosphonium chloride, 1,8-diazabicyclo[5.4.0]undec-7-ene and benzyldiphenyl(dimethylamino)phosphonium chloride. Other suitable curing accelerators include methyltrioctylammonium chloride, methyltributylammonium chloride, tetrapropylammonium chloride, benzyltrioctylphosphonium bromide, benzyltrioctylphosphonium chloride, methyltrioctylphosphonium acetate, tetraoctylphosphonium bromide, methyltriphenylarsonium tetrafluoroborate, tetraphenylantimony bromide, 4-chlorobenzyltriphenylphosphonium chloride, 8-benzyl-1,8-diazabicyclo(5.4.0)-7-undecenyl chloride, diphenylmethyltriphenylphosphonium chloride, allyltriphenylphosphonium chloride, tetrabutylphosphonium bromide, m-trifluoromethyl-benzyltrioctylphosphonium chloride, and other quaternary compounds disclosed in U.S. Patent Nos. 5,591,804; 4,912,171; 4,882,390; 4,259,463; 4,250,278 and 3,876,654.

[0071] In some embodiments, the curable fluorinated elastomer is a peroxide-curable fluorinated elastomer, and the curable fluorinated elastomer composition is a peroxide-curable fluorinated elastomer composition further comprising a peroxide curing agent.

[0072] Suitable peroxide curing agents can include but are not limited to triallyl isocyanurate (TAIC), 1,1-bis(tert-butylperoxy)-3,5,5-trimethylcyclohexane, 2,5-dimethylhexane-2,5-dihydroperoxide, di-tert-butyl peroxide, tert-butyl cumyl peroxide, dicumyl peroxide, α,α-bis(tert-butylperoxy)-p-diisopropylbenzene, 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane, 2,5-dimethyl-2,5-bis(tert-butylperoxy)-hex-3-yne, benzoyl peroxide, tert-butyl peroxybenzene, tert-butyl peroxymaleic acid, tert-butyl peroxyisopropyl carbonate, and / or tert-butyl peroxybenzoate.

[0073] Suitable amounts of peroxide curing agents in peroxide-curable fluororubber compositions can include, but are not limited to, from about 3.0 phr to about 5.0 phr, from about 3.2 phr to about 4.8 phr, from about 3.4 phr to about 4.6 phr, from about 3.6 to about 4.4 phr, from about 3.8 phr to about 4.2 phr, about 4 phr, or any value, range, or sub-range therebetween.

[0074] Suitable weak acid acceptors can include, but are not limited to, zinc oxide, lead oxide, and / or hydrotalcite.

[0075] Suitable amounts of weak acid acceptors can include, but are not limited to, about 1 phr or less, from about 0.1 phr to about 1 phr, from about 0.2 phr to about 0.8 phr, about 0.5 phr or less, from about 0.2 to about 0.5 phr, or any value, range, or sub-range therebetween.

[0076] In some embodiments, the curable fluororubber composition contains less than 1.0 phr, such as, for example, less than 0.1 phr, of magnesium oxide and calcium hydroxide in combined form. In some embodiments, the curable fluororubber composition is free or substantially free of magnesium oxide and calcium hydroxide.

[0077] In some embodiments, the cured fluororubber formed from the curable fluororubber composition comprises the curable fluororubber, a dehydrohalogenating agent, an acid acceptor comprising bismuth oxide (Bi 2 O 3 ) present in the curable fluororubber composition in an amount of at least 3 parts per hundred parts by weight of the curable fluororubber, and at least one silicon-containing chemical present in the curable fluororubber composition in an amount of at least 0.05 parts per hundred parts by weight of the curable fluororubber.

[0078] In some embodiments, the cured fluororubber has a coefficient of static friction of less than 0.5, such as, for example, from 0.2 to 0.4.

[0079] In some embodiments, the cured fluororubber has a coefficient of dynamic friction of less than 0.5, such as, for example, from 0.15 to 0.4.

[0080] In some embodiments, the cured fluororubber has a tensile strength of 9.0 MPa to 25 MPa.

[0081] In some embodiments, the cured fluororubber has an elongation at break of 150% to 200%.

[0082] In some embodiments, a method of curing a curable fluorinated elastomer includes forming a curable fluorinated elastomer composition and heating the curable fluorinated elastomer composition to a curing temperature to cure the curable fluorinated elastomer. The curable fluorinated elastomer composition comprises the curable fluorinated elastomer, a dehydrohalogenating agent, an acid acceptor comprising bismuth oxide (Bi 2 O 3 ) present in the curable fluorinated elastomer composition in an amount of at least 3 parts per hundred parts by weight of the curable fluorinated elastomer, and at least one silicone-containing chemical present in the curable fluorinated elastomer composition in an amount of at least 0.05 parts per hundred parts by weight of the curable fluorinated elastomer.

[0083] In some embodiments, the curable fluorinated elastomer composition is cured under conventional curing conditions.

[0084] In some embodiments, heating includes pressure curing.

[0085] Suitable curing temperatures for heating can include, but are not limited to, about 160 °C to about 190 °C, about 165 °C to about 185 °C, about 170 °C to about 180 °C, about 170 °C, about 180 °C, or any value, range, or sub-range therebetween.

[0086] Suitable curing times for heating can depend on the curing temperature and can include, but are not limited to, about 5 minutes to about 90 minutes, about 5 minutes to about 60 minutes, about 5 minutes to about 40 minutes, about 10 minutes to about 30 minutes, about 5 minutes to about 20 minutes, or any value, range, or sub-range therebetween.

[0087] In some embodiments, the method further includes post-curing the cured fluorinated elastomer at a post-curing temperature for a post-curing period.

[0088] Suitable post-curing temperatures can include, but are not limited to, about 200 °C to about 260 °C, about 210 °C to about 250 °C, about 220 °C to about 240 °C, about 225 °C to about 235 °C, about 230 °C, or any value, range, or sub-range therebetween.

[0089] Suitable post-curing times can depend on the post-curing temperature and can include, but are not limited to, about 15 minutes or longer, about 15 minutes to about 24 hours, about 15 minutes to about 16 hours, about 15 minutes to about 8 hours, about 15 minutes to about 4 hours, about 15 minutes to about 2 hours, about 15 minutes to about 1 hour, or any value, range, or sub-range therebetween.

[0090] Without being bound by theory, it is believed that the availability of hydrogen fluoride (HF) results in the formation of a low-friction layer on the cured fluorinated elastomer of the present invention through the reaction of HF with Si-containing chemicals to form orthosilicic acid (Si(OH) 4 ) at the surface of the cured fluorinated elastomer. The curing reaction in the polyhydroxy curing system (such as with BpAF) generates HF, but strong acid acceptors (such as magnesium oxide and calcium hydroxide) capture HF, thus preventing it from reacting with Si-containing chemicals. It is believed that bismuth oxide as an acid acceptor allows the curing process to continue while allowing some HF to be available for reaction with Si-containing chemicals.

[0091] In contrast, it is believed that the pure peroxide curing system does not generate HF for reaction with Si-containing chemicals to form a low-friction surface layer, but some BpAF can be included as a dehydrohalogenating agent to generate some HF for forming a low-friction surface layer in the presence of bismuth oxide and Si-containing chemicals (and in some cases in the absence of bismuth oxide).

[0092] Testing method

[0093] Static friction coefficient and dynamic friction coefficient

[0094] The static and dynamic coefficient of friction were measured using a Shimadzu Autograph AGS-5kNX tester. These values were calculated by the force of dragging a stainless-steel reference material at a rate of 100 mm / min over a cured fluorinated elastomer sheet sample.

[0095] Tensile strength and elongation at break

[0096] The tensile strength (in MPa) and elongation at break (in %) of the cured and unaged fluorinated elastomer were determined at 23 °C by the ISO 37:2011 test protocol.

[0097] Examples

[0098] Examples of curing fluorine-containing elastomers for comparison

[0099] The comparative fluorinated elastomer curing compositions comprise a curable fluorinated elastomer, 30 parts by weight per 100 parts of curable fluorinated elastomer (phr) of carbon black filler, and the amounts of dehydrohalogenating agent and acid acceptor shown in Tables 1 to 4. Certain comparative fluorinated elastomer curing compositions further comprise accelerators, Si-containing chemicals, and / or processing aids indicated in phr in Tables 1 to 4.

[0100] Examples of curing fluorine-containing elastomers of the present invention

[0101] The fluorine-containing elastomer curing composition of the present invention comprises a curable fluorine-containing elastomer, 30 phr of carbon black filler, and a dehydrohalogenating agent, Bi 2 O 3 acid acceptor and Si-containing chemical, except that Example 10 of the present invention only contains 5 phr of carbon black filler, and some of the listed Si-containing chemicals also serve as fillers. Certain fluorine-containing elastomer curing compositions of the present invention further comprise a promoter, a processing aid, and / or an additional acid acceptor indicated in phr in Tables 1 to 4.

[0102] Curing results and curing properties of fluorine-containing elastomers

[0103] The fluorine-containing elastomer curing composition is pressure-cured at a pressure-curing temperature in the range of 170 °C to 180 °C for a pressure-curing time in the range of 7 minutes to 60 minutes. Then, the cured fluorine-containing elastomer is post-cured at a post-curing temperature of 230 °C for a post-curing time in the range of 30 minutes to 24 hours, except for Comparative Example 7 and Comparative Example 8, where Comparative Example 7 was not cured and Comparative Example 8 was not post-cured.

[0104] Effect of acid acceptor and Si-containing chemicals on friction properties

[0105] Table 1 shows that the presence of bismuth oxide and Si-containing chemicals in combination in the curable fluorine-containing elastomer composition produces a cured fluorine-containing elastomer with low friction.

[0106] In Examples 1 to 8 of the present invention, the combination of different types and amounts of Si-containing chemicals with bismuth oxide as the sole acid acceptor produces a cured fluorine-containing elastomer having a static coefficient in the range of 0.18 to 0.34 and a dynamic friction coefficient in the range of 0.16 to 0.32. The Si-containing chemicals in Examples 1 to 8 of the present invention are respectively: silica (1.1), sodium salt of silicic acid (1), silica (2), silica (3), silica (4), silica (5), γ-aminopropyltriethoxysilane (6), vinyltriethoxysilane (7), a combination of silicone and silica (8), and wollastonite (9).

[0107] Example 9 of the present invention shows that further comprising a small amount of a weak acid acceptor (zinc oxide) does not adversely affect the friction performance of the resulting cured fluorine-containing elastomer.

[0108] Table 1: Compositions of different acid acceptors and Si-containing chemicals

[0109]

[0110] Comparative Example 1 shows that in the absence of Si-containing chemicals, bismuth oxide as an acid acceptor does not provide a cured fluorine-containing elastomer with low friction.

[0111] Comparative Examples 2 and 3 show that the standard acid acceptor combination of 3 phr magnesium oxide and 6 phr calcium hydroxide (both strong acid acceptors) in place of bismuth oxide does not provide a cured fluorine-containing elastomer with low friction, either in the absence or presence of Si-containing chemicals.

[0112] Finally, Comparative Examples 4 and 5 show that the presence of only 1 phr magnesium oxide or calcium hydroxide disrupts the ability of the combination of bismuth oxide and Si-containing chemicals to provide a cured fluorine-containing elastomer with low friction. Comparative Example 1.1 shows that a relatively low amount (0.01 phr) of Si-containing chemicals results in relatively poor frictional properties of the resulting cured fluorine-containing elastomer.

[0113] Dehydrohalogenating agent and amount of Bi 2 O 3 Effect on friction performance

[0114] Example 10 of the present invention in Table 2 shows that an amount of BpAF dehydrohalogenating agent as low as 1.28 phr is sufficient to produce a cured fluorine-containing elastomer with low friction, while 0.96 phr of BpAF in Comparative Example 6 is insufficient. Compositions containing 1.12 phr of alternative dehydrohalogenating agents methylhydroquinone and 2-methylresorcinol, which are Examples 11 and 12 of the present invention in place of BpAF, can also provide a cured fluorine-containing elastomer with low friction.

[0115] Table 2: Composition of different dehydrohalogenating agents and amount of Bi 2 O 3 quantity

[0116]

[0117] Example 13 of the present invention shows that an amount of Bi 2 O 3 as low as 5 phr is sufficient to produce a cured fluorine-containing elastomer with low friction, while 1 phr of bismuth oxide in Comparative Example 7 fails to cure.

[0118] Effect of post-curing on friction properties

[0119] Table 3 shows that the composition of Comparative Example 8 without post-curing did not obtain a cured fluorine-containing elastomer with low friction.

[0120] Table 3: Composition of different dehydrohalogenating agents and the amount of Bi 2 O 3 quantity

[0121]

[0122] Examples 14 to 16 of the present invention have the same composition as Comparative Example 8, but are post-cured at 230 °C for the time amounts indicated in Table 3. A post-curing time of only 30 minutes at 230 °C is sufficient to produce a cured fluorine-containing elastomer with low friction, and increasing the post-curing time up to 24 hours does not further reduce the coefficient of friction.

[0123] Effect of curable fluorine-containing elastomers on friction properties

[0124] Table 4 shows that compositions of peroxide (PO)-curable fluorine-containing elastomers can also be cured into low-friction cured fluorine-containing elastomers by including appropriate amounts of bismuth oxide and Si-containing chemicals in the compositions. Examples 17, 18, and 19 of the present invention each contain different PO-curable fluorine-containing elastomers having 66% F, 68% F, and 64% F, respectively. The compositions of Table 4 also contain 1.5 phr of 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane and 2.5 phr of triallyl isocyanurate (TAIC) as peroxide curing agents.

[0125] Table 4: Compositions of peroxide-curable fluorine-containing elastomers

[0126]

[0127] In contrast, Comparative Example 9 lacks bismuth oxide and Comparative Example 10 lacks Si-containing chemicals, and neither of these two compositions produces a low-friction cured fluorine-containing elastomer.

[0128] The tensile strength and elongation at break of the peroxide-curable compositions of Table 4 were measured (data not shown). Although the examples of the present invention in Table 4 have favorable low-friction properties, they also have lower tensile strength and lower elongation at break than the comparative examples in Table 4, which was not observed in the polyhydroxy-curable fluorine-containing elastomers.

[0129] In addition to the different PO-curable fluorine-containing elastomers of Table 4, compositions containing Bi 2 O 3 and Si-containing chemicals and containing different BpAF-curable fluorine-containing elastomers (having different F contents in the range of 66% to 70%) were tested, and these compositions produced low-friction cured fluorine-containing elastomers (data not shown).

[0130] All of the above references are hereby incorporated herein by reference.

[0131] Although the present invention has been described with reference to the preferred embodiments, those skilled in the art should understand that various changes can be made and elements thereof can be replaced with equivalents without departing from the scope of the present invention. In addition, various modifications can be made to adapt a particular situation or particular material to the teachings of the present invention without departing from the essential scope of the present invention. Therefore, the present invention is not intended to be limited to the specific embodiments disclosed as the best contemplated mode for carrying out the present invention, but rather the present invention will include all embodiments falling within the scope of the appended claims.

Claims

1. A curable fluorine-containing elastomer composition, the curable fluorine-containing elastomer composition comprising: A curable fluorine-containing elastomer; A dehydrohalogenating agent; An acid acceptor containing bismuth oxide (Bi 2 O 3 ), which is present in the curable fluorine-containing elastomer composition in an amount of at least 3 parts per 100 parts by weight of the curable fluorine-containing elastomer; and At least one silicon-containing chemical, the at least one silicon-containing chemical being present in the curable fluorine-containing elastomer composition in an amount of at least 0.05 parts per hundred parts by weight of the curable fluorine-containing elastomer.

2. The curable fluorine-containing elastomer composition according to claim 1, wherein the bismuth oxide is present in the curable fluorine-containing elastomer composition in an amount of 5 parts per hundred parts by weight to 15 parts per hundred parts by weight of the curable fluorine-containing elastomer.

3. The curable fluorine-containing elastomer composition according to claim 1 or 2, wherein the at least one silicon-containing chemical is present in the curable fluorine-containing elastomer composition in an amount of 0.05 parts per hundred parts by weight to 5 parts per hundred parts by weight of the curable fluorine-containing elastomer.

4. The curable fluorine-containing elastomer composition according to any one of the preceding claims, wherein the at least one silicon-containing chemical is selected from the group consisting of silica, calcium silicate (Ca 2 SiO 4 ), calcium metasilicate (CaSiO 3 ), silicone, γ-aminopropyltriethoxysilane, vinyltriethoxysilane, and combinations thereof.

5. The curable fluorine-containing elastomer composition according to any one of the preceding claims, wherein the dehydrohalogenating agent is present in the curable fluorine-containing elastomer composition in an amount of at least 1.0 part per hundred parts by weight of the curable fluorine-containing elastomer.

6. The curable fluorine-containing elastomer composition according to any one of the preceding claims, wherein the dehydrohalogenating agent is selected from the group consisting of 2,2-bis(4-hydroxyphenyl)hexafluoropropane, methylhydroquinone, and 2-methylresorcinol.

7. The curable fluorine-containing elastomer composition according to any one of the preceding claims, wherein the curable fluorine-containing elastomer comprises a peroxide-curable fluorine-containing elastomer capable of being cured by a peroxide curing system, and the curable fluorine-containing elastomer composition further comprises a peroxide curing agent.

8. The curable fluorine-containing elastomer composition according to any one of the preceding claims, wherein the curable fluorine-containing elastomer composition contains less than 0.1 part per hundred parts by weight of the curable fluorine-containing elastomer of magnesium oxide and calcium hydroxide in combination.

9. The curable fluorine-containing elastomer composition according to any one of the preceding claims, wherein the curable fluorine-containing elastomer composition does not contain or substantially does not contain magnesium oxide and calcium hydroxide.

10. The curable fluorine-containing elastomer composition according to claim 1, wherein the curable fluorine-containing elastomer is a dimer of hexafluoropropene and vinylidene fluoride.

11. A cured fluorine-containing elastomer cured from a curable fluorine-containing elastomer composition, the curable fluorine-containing elastomer composition comprising: A curable fluorine-containing elastomer; A dehydrohalogenating agent; An acid acceptor containing bismuth oxide (Bi 2 O 3 ), wherein the acid acceptor is present in the curable fluorine-containing elastomer composition in an amount of at least 3 parts per 100 parts by weight of the curable fluorine-containing elastomer; and At least one silicon-containing chemical, the at least one silicon-containing chemical being present in the curable fluorine-containing elastomer composition in an amount of at least 0.05 parts per hundred parts by weight of the curable fluorine-containing elastomer.

12. The cured fluorine-containing elastomer according to claim 11, wherein the bismuth oxide is present in the curable fluorine-containing elastomer composition in an amount of 5 parts per hundred parts by weight to 15 parts per hundred parts by weight of the curable fluorine-containing elastomer.

13. The cured fluorinated elastomer according to claim 11 or 12, wherein the at least one silicon-containing chemical is present in the curable fluorinated elastomer composition in an amount of 0.05 parts per hundred parts by weight to 5 parts per hundred parts by weight of the curable fluorinated elastomer.

14. The cured fluorine-containing elastomer according to any one of claims 11 to 13, wherein the at least one silicon-containing chemical is selected from the group consisting of silica, calcium silicate (Ca 2 SiO 4 ), calcium metasilicate (CaSiO 3 ), silicone, γ-aminopropyltriethoxysilane, vinyltriethoxysilane, and combinations thereof.

15. The cured fluorinated elastomer according to any one of claims 11 to 14, wherein the dehydrohalogenating agent is present in the curable fluorinated elastomer composition in an amount of at least 1.0 part per hundred parts by weight of the curable fluorinated elastomer.

16. The cured fluorinated elastomer according to any one of claims 11 to 15, wherein the dehydrohalogenating agent is selected from the group consisting of 2,2-bis(4-hydroxyphenyl)hexafluoropropane, methylhydroquinone, and 2-methylresorcinol.

17. The cured fluorinated elastomer according to any one of claims 11 to 16, wherein the curable fluorinated elastomer comprises a peroxide-curable fluorinated elastomer capable of being cured by a peroxide curing system, and the cured fluorinated elastomer further comprises a peroxide curing agent.

18. The cured fluorinated elastomer according to any one of claims 11 to 17, wherein the curable fluorinated elastomer composition contains less than 0.1 part per hundred parts by weight of the curable fluorinated elastomer of magnesium oxide and calcium hydroxide in combination.

19. The cured fluorinated elastomer according to any one of claims 11 to 18, wherein the cured fluorinated elastomer is free or substantially free of magnesium oxide and calcium hydroxide.

20. The cured fluorinated elastomer according to any one of claims 11 to 19, wherein the cured fluorinated elastomer has a static coefficient of friction of less than 0.

5.

21. The cured fluorinated elastomer according to any one of claims 11 to 20, wherein the cured fluorinated elastomer has a static coefficient of friction of 0.2 to 0.

4.

22. The cured fluorinated elastomer according to any one of claims 11 to 21, wherein the cured fluorinated elastomer has a dynamic coefficient of friction of less than 0.

5.

23. The cured fluorinated elastomer according to any one of claims 11 to 22, wherein the cured fluorinated elastomer has a dynamic coefficient of friction of 0.15 to 0.

4.

24. The cured fluorinated elastomer according to any one of claims 11 to 23, wherein the cured fluorinated elastomer has a tensile strength of 9.0 MPa to 25 MPa.

25. The cured fluorinated elastomer according to any one of claims 11 to 24, wherein the cured fluorinated elastomer has an elongation at break of 150% to 200%.

26. A method for curing a curable fluorinated elastomer, the method comprising: forming a curable fluorinated elastomer composition, the curable fluorinated elastomer composition comprising the curable fluorinated elastomer; a dehydrohalogenating agent; An acid acceptor containing bismuth oxide (Bi 2 O 3 ), wherein the acid acceptor is present in the curable fluorine-containing elastomer composition in an amount of at least 3 parts per 100 parts by weight of the curable fluorine-containing elastomer; and at least one silicon-containing chemical, wherein the at least one silicon-containing chemical is present in the curable fluorine-containing elastomer composition in an amount of at least 0.05 parts per hundred parts by weight of the curable fluorine-containing elastomer; and heating the curable fluorine-containing elastomer composition to a curing temperature for a curing time sufficient to cure the curable fluorine-containing elastomer.

27. The method according to claim 26, wherein the heating comprises pressure curing the curable fluorine-containing elastomer composition, and wherein the curing temperature is in the range of about 160 °C to about 190 °C, and the curing time is in the range of about 5 minutes to about 90 minutes.

28. The method according to claim 26 or 27, the method further comprising post-curing the cured fluorine-containing elastomer at a post-curing temperature for a post-curing time.

29. The method according to claim 28, wherein the post-curing temperature is in the range of about 200 °C to about 260 °C, and the post-curing time is about 15 minutes or longer.

30. The method according to any one of claims 26 to 29, wherein the bismuth oxide is present in the curable fluorine-containing elastomer composition in an amount of 5 parts per hundred parts by weight to 15 parts per hundred parts by weight of the curable fluorine-containing elastomer.

31. The method according to any one of claims 26 to 30, wherein the at least one silicon-containing chemical is present in the curable fluorine-containing elastomer composition in an amount of 0.05 parts per hundred parts by weight to 5 parts per hundred parts by weight of the curable fluorine-containing elastomer.

32. The method according to any one of claims 26 to 31, wherein the at least one silicon-containing chemical is selected from the group consisting of silica, calcium silicate (Ca 2 SiO 4 ), calcium metasilicate (CaSiO 3 ), silicone, γ-aminopropyltriethoxysilane, vinyltriethoxysilane, and combinations thereof.

33. The method according to any one of claims 26 to 32, wherein the dehydrohalogenating agent is present in the curable fluorine-containing elastomer composition in an amount of at least 1.0 part per hundred parts by weight of the curable fluorine-containing elastomer.

34. The method according to any one of claims 26 to 33, wherein the dehydrohalogenating agent is selected from the group consisting of 2,2-bis(4-hydroxyphenyl)hexafluoropropane, methylhydroquinone, 2 and 2-methylresorcinol.

35. The method according to any one of claims 26 to 34, wherein the curable fluorine-containing elastomer comprises a peroxide-curable fluorine-containing elastomer capable of being cured by a peroxide curing system, and the curable fluorine-containing elastomer composition further comprises a peroxide curing agent.

36. The method according to any one of claims 26 to 35, wherein the curable fluorine-containing elastomer composition contains less than 0.1 part per hundred parts by weight of the curable fluorine-containing elastomer of magnesium oxide and calcium hydroxide in combination.

37. The method according to any one of claims 26 to 36, wherein the cured fluorine-containing elastomer is free or substantially free of magnesium oxide and calcium hydroxide.

38. The method according to any one of claims 26 to 37, wherein the cured fluorine-containing elastomer has a static coefficient of friction of less than 0.

5.

39. The method according to any one of claims 26 to 38, wherein the cured fluorine-containing elastomer has a static coefficient of friction of 0.2 to 0.

4.

40. The method according to any one of claims 26 to 39, wherein the cured fluorine-containing elastomer has a dynamic coefficient of friction of less than 0.

5.

41. The method according to any one of claims 26 to 40, wherein the cured fluorine-containing elastomer has a dynamic coefficient of friction of 0.15 to 0.4.

Images