FLUORINATED COPOLYMER, FLUORINATED COPOLYMER COMPOSITION, AND CROSSLINKED RUBBER ARTICLE

Abstract

To provide a fluorinated copolymer, whereby it is possible to produce a crosslinked rubber article excellent in mold release properties.

The fluorinated copolymer of the present invention has units based on tetrafluoroethylene, units based on a perfluoro(alkyl vinyl ether), units based on a monomer having a fluorine atom and at least two polymerizable unsaturated bonds, and units based on a monomer having a nitrile group and a fluorine atom.

Claims

1. A fluorinated copolymer having units based on tetrafluoroethylene, units based on a perfluoro(alkyl vinyl ether), units based on a monomer having a fluorine atom and at least two polymerizable unsaturated bonds, and units based on a monomer having a nitrile group and a fluorine atom.

2. The fluorinated copolymer according to claim 1, of which the storage modulus G′ is at least 470 kPa.

3. The fluorinated copolymer according to claim 1, wherein the molar ratio of the content of the units based on the monomer having a fluorine atom and at least two polymerizable unsaturated bonds to the content of the units based on the monomer having a nitrile group and a fluorine atom, is from 0.002 to 20.

4. The fluorinated copolymer according to claim 1, wherein the perfluoro(alkyl vinyl ether) is a monomer represented by the following formula (1):
CF.sub.2═CF—O—R.sup.f1   (1) in the formula (1), R.sup.f1 represents a C.sub.1-10 perfluoroalkyl group.

5. The fluorinated copolymer according to claim 1, wherein the monomer having a fluorine atom and at least two polymerizable unsaturated bonds is a monomer represented by the following formula (2):
(CR.sup.21R.sup.22═CR.sup.23).sub.a2R.sup.24   (2) in the formula (2), R.sup.21, R.sup.22 and R.sup.23 each independently represent a hydrogen atom, a fluorine atom, a methyl group or a trifluoromethyl group, a2 represents an integer of from 2 to 6, R.sup.24 represents an a2 valent C.sub.1-10 perfluorohydrocarbon group or a group having an etheric oxygen atom at the terminal or between carbon-carbon atoms of the perfluorohydrocarbon group, and the plurality of R.sup.21, the plurality of R.sup.22 and the plurality of R.sup.23 may, respectively, be the same or different from one another.

6. The fluorinated copolymer according to claim 5, wherein the monomer represented by the formula (2) is a monomer represented by the following formula (3) or a monomer represented by the following formula (4):
(CF.sub.2═CF).sub.2R.sup.31   (3) in the formula (3), R.sup.31 is a divalent C.sub.1-10 perfluorohydrocarbon group or a group having an etheric oxygen atom at the terminal or between carbon-carbon atoms of the perfluorohydrocarbon group,
(CH.sub.2═CH).sub.2R.sup.41   (4) in the formula (4), R.sup.41 is a divalent C.sub.1-10 perfluorohydrocarbon group or a group having an etheric oxygen atom at the terminal or between carbon-carbon atoms of the perfluorohydrocarbon group.

7. The fluorinated copolymer according to claim 1, wherein the monomer having a nitrile group and a fluorine atom is a monomer represented by the following formula (5):
CR.sup.51R.sup.52═CR.sup.53—R.sup.54—CN   (5) in the formula (5), R.sup.51, R.sup.52 and R.sup.53 each independently represent a hydrogen atom, a fluorine atom or a methyl group, and R.sup.54 is a divalent C.sub.1-10 perfluorohydrocarbon group or a group having an etheric oxygen atom at the terminal or between carbon-carbon atoms of the perfluorohydrocarbon group.

8. The fluorinated copolymer according to claim 1, wherein to all units of the fluorinated copolymer, the content of units based on tetrafluoroethylene is from 59 to 80 mol %, the content of units based on a perfluoro(alkyl vinyl ether) is from 19 to 40 mol %, the content of units based on a monomer having a fluorine atom and at least two polymerizable unsaturated bonds is from 0.01 to 1.0 mol %, and the content of units based on a monomer having a nitrile group and a fluorine atom is from 0.05 to 5 mol %.

9. The fluorinated copolymer according to claim 1, wherein the fluorinated copolymer has an iodine atom.

10. A fluorinated copolymer composition comprising the fluorinated copolymer as defined in claim 1 and at least one of a crosslinking agent and a catalyst.

11. The fluorinated copolymer composition according to claim 10, which does not substantially contain a mold release agent.

12. A crosslinked rubber article having the fluorinated copolymer in the fluorinated copolymer composition as defined in claim 10 crosslinked.

Description

EXAMPLES

[0130] In the following, the present invention will be described in detail with reference to Examples. Ex. 1 to Ex. 6 are Examples of the present invention, and Ex. 7 and 8 are Comparative Examples. However, the present invention is not limited to these Examples. Further, the contents of the respective components in the Tables given later, are based on mass, unless otherwise specified.

[Content of Units Based on the Respective Monomers in the Fluorinated Copolymer]

[0131] The content (mol %) of DVE units to all units of the fluorinated copolymer was calculated based on the amount of DVE used in the production of the fluorinated copolymer (amount of DVE used).

[0132] Further, the contents (mol %) of TFE units, PAVE units and R.sub.CN units to all units of the fluorinated copolymer were calculated based on the .sup.19F-nuclear magnetic resonance (NMR) analyses.

<Calculation of the Content of DVE Units to All Units of the Fluorinated Copolymer>

[0133] The filtrate after coagulating the latex after polymerization to remove the fluorinated copolymer and the filtrate remaining after washing the latex were filtered, through a disc filter, to obtain the resulting liquid, which was analyzed by an ion chromatography measurement device (manufactured by Dia Instruments Co. Ltd., a device having a pretreatment apparatus AQF-100 Model for automatic sample combustion device ion chromatograph and an ion chromatograph combined).

[0134] In a case where at least 3 mass % of fluoride ions to the charged amount of DVE are detected, as the amount of DVE used, a value obtained by subtracting the amount of DVE in the liquid calculated based on the above results of the ion chromatography measurement from the amount of DVE added to the reactor (the amount of DVE charged) was used.

[0135] On the other hand, in a case where at least 3 mass % of fluoride ions to the charged amount of DVE are not detected, it is assumed that all the DVE used for charging has been polymerized, and as the amount of DVE used, the amount of DVE charged was used.

[0136] Based on the amount of DVE units used, thus obtained, the content (mol %) of DVE units to all units of the fluorinated copolymer was calculated.

[Storage Modulus G′ of Fluorinated Copolymer]

[0137] Using rubber processing analysis system (manufactured by Alpha Technologies, Inc. RPA2000), in accordance with ASTM D6204, a value measured under conditions of a temperature of 100° C., an amplitude of 0.5 degree, and a vibration frequency of 50 times/min., was adopted as the storage modulus G′ of the fluorinated copolymer. The storage modulus G′ of the fluorinated copolymer is an index for the flowability at the time of molding of a crosslinked rubber article.

[Storage Modulus G′.sub.0.1 and G′.sub.1 of Fluorinated Copolymer]

[0138] Using rubber processing analysis system (manufactured by Alpha Technologies, Inc. RPA2000), in accordance with ASTM D4440, values measured under conditions of a temperature of 140° C. and shear rates of 0.1 degree/second and 1 degree/second, respectively, were adopted as the storage modulus G′.sub.0.1 and G′.sub.1 of the fluorinated copolymer.

[Degree of Crosslinking in Fluorinated Copolymer Composition]

[0139] With respect to the fluorinated copolymer composition, the crosslinking properties of the fluorinated copolymer composition were measured by using a crosslinking property measuring instrument (manufactured by Alfa Technologies, Inc., product name “RPA2000”) in accordance with ASTM D5289 under conditions of 177° C. for 12 minutes at an amplitude of 3 degrees.

[0140] M.sub.H to be measured represents the maximum value of torque, M.sub.L represents the minimum value of torque, and M.sub.H-M.sub.L (M.sub.H minus M.sub.L) represents the degree of crosslinking (unit: dNm). The crosslinking properties are an index for the crosslinking reactivity of the fluorinated copolymer, and the larger the value of M.sub.H-M.sub.L, the better the crosslinking reactivity.

[Specific Gravities of Fluorinated Copolymer and Crosslinked Rubber Article]

[0141] With respect to the fluorinated copolymer and the crosslinked rubber article, the specific gravities were measured by using a specific gravity meter (manufactured by Shinko Denshi Co., Ltd.) in accordance with JIS K6220-1: 2015.

[Tensile Strength, 100% Modulus and Tensile Elongation of Crosslinked Rubber Article]

[0142] Using a test specimen having a plate-shaped crosslinked rubber article (thickness: 1 mm) punched out by a No. 4 dumbbell, the tensile strength, 100% modulus and tensile elongation were measured in accordance with JIS K6251: 2010 (corresponding international standard ISO 37:2005).

[0143] Here, as the measuring device, a tensile testing machine with data processing means (Quick Reader TS-2530, manufactured by Ueshima Seisakusho Co., Ltd.) was used.

[0144] Each test was conducted by using three test specimens, and the arithmetic mean value of the measured values of the three test specimens was recorded.

[Hardness]

[0145] Using a test specimen of the crosslinked rubber article, the hardness (Shore-A) was measured by using a type A durometer in accordance with JIS K6253: 2012.

[0146] Here, as the measuring device, an automatic hardness tester for rubber (Digitest Shore-A, manufactured by H. Bareiss) was used.

[0147] The test was conducted by using three test specimens, and the arithmetic mean value of the measured values of the three test specimens was recorded.

[Compression Set]

[0148] Using a test specimen of the crosslinked rubber article, the compression set (%) when the test specimen was held at 250° C. for 70 hours was measured in accordance with JIS K6262. The smaller the value of the compression set, the better the recovery property of the crosslinked rubber article, i.e., the better the crosslinking.

[0149] The test was conducted by using three test specimens, and the arithmetic mean value of the measured values of the three test specimens was recorded.

[Heat Aging Test]

[0150] The thickness of a test specimen of the crosslinked rubber article was measured by a thickness gauge, and then, the test specimen was heated at 300° C. for 70 hours under an air atmosphere (heat aging).

[0151] After cooling the test specimen to room temperature after heat aging, the tensile strength, 100% modulus and tensile elongation after heat aging were measured by using the cooled test specimen under the same conditions as the above described test method.

[0152] The test was conducted by using three test specimens, and the arithmetic mean value of the measured values of the three test specimens was recorded. The rate of change before and after the heat aging test (heat aging test change rate) was calculated in accordance with the following formula, based on the measured value of the test specimen not subjected to heat aging (normal test value) and the measured value of the test specimen after heat aging (test value after heat aging). The closer the rate of change to 0%, the better the heat resistance.

[0153] Heat aging test change rate (%)=100×{(normal test value)−(test value after heat aging)}/(normal test value)

[Mold Release Property Test]

[0154] By introducing the fluorinated copolymer composition into a sheet-shaped mold, the fluorinated copolymer composition was crosslinked at 180° C. for 20 minutes to obtain a crosslinked rubber article (100 mm in length×60 mm in width×1 mm in thickness). After the crosslinking reaction was completed, air was immediately sprayed to the interface between the crosslinked rubber article and the mold by using an air gun (product name: Cyclone Duster, manufactured by Chuo Kuki Co., Ltd.), and the mold release properties were evaluated in accordance with the following evaluation standards.

[0155] Here, since air is injected immediately after the completion of the crosslinking reaction, the temperature of the crosslinked article at the time of air injection is considered to be close to 180° C.

<Conditions for Air Injection by Air Gun>

[0156] Pressure: 0.5 MPa [0157] Air injection time: 3 seconds

<Evaluation Standards>

[0158] O: The crosslinked rubber article was detached from the mold. [0159] x: The crosslinked rubber article did not detach from the mold.

[Ex. 1]

<Production of Fluorinated Copolymer 1>

[0160] A stainless steel pressure-resistant reactor with an internal volume of 20 L equipped with anchor blades was degassed, and then, 7.2 L of ultrapure water, 880 g of a 30 mass % solution of C.sub.2F.sub.5OCF.sub.2CF.sub.2OCF.sub.2COONH.sub.4 as an emulsifier, 7.3 g of 8CNVE, 17.7 g of C3DVE, and 15.9 g of a 5 mass % aqueous solution of disodium hydrogen phosphate 12 hydrate, were charged, and the gas phase was replaced with nitrogen. While stirring with the anchor blades at a speed of 375 rpm, 137 g of TFE and 635 g of PMVE were injected under pressure into the vessel, and then, the internal temperature was raised to 80° C. The reactor internal pressure was 0.90 MPa [gauge]. 40 mL of a 3 mass % aqueous solution of ammonium persulfate (APS) was added, to initiate polymerization. The addition ratio of the monomers injected under pressure before the initiation of polymerization (hereinafter referred to as “initially added monomers”) as expressed by a molar ratio, was TFE:PMVE:8CNVE:C3DVE=26.0:72.6:0.4:1.0.

[0161] After the initiation of polymerization, monomers were injected under pressure as follows as the polymerization progressed. Hereafter, injection of monomers under pressure after the initiation of polymerization will be referred to also as “post-adding” and monomers to be injected under pressure after the initiation of polymerization will be referred to also as “post-added monomers”.

[0162] At the time when the reactor internal pressure dropped to 0.89 MPa [gauge], TFE was injected under pressure, and the reactor internal pressure was raised to 0.90 MPa [gauge]. This operation was repeated, and each time when 119.3 g of TFE was injected under pressure, 3.6 g of 8CNVE, 74 g of PMVE and 3.6 g of 8CNVE, were injected under pressure in this order.

[0163] At the time when the polymerization speed decreased, a 3 mass % aqueous solution of APS was optionally added. The total of the 3 mass % aqueous solution of APS added after the initiation of polymerization was 51 mL.

[0164] Upon completion of the cycle when the total added mass of TFE became to be 1,073.7 g, 119.3 g of TFE was injected under pressure. At the time when the total mass of post-added TFE reached 1,193 g, the addition of post-added monomers was stopped, and the reactor internal temperature was cooled to 10° C. to stop the polymerization reaction and to obtain a latex containing a fluorinated copolymer. The polymerization time was 375 minutes. Further, the total added masses of the respective post-added monomers were 1,193 g of TFE, 666 g of PMVE and 64.8 g of 8CNVE, which can be converted into the molar ratio of TFE:PMVE:8CNVE=74.1:24.9:1.0.

[0165] The latex was added to a 5 mass % aqueous solution of potassium aluminum sulfate to flocculate and separate the fluorinated copolymer. The fluorinated copolymer was filtered, washed with ultrapure water, and vacuum dried at 50° C., to obtain white fluorinated copolymer 1. The contents (molar ratio) of the respective units in the obtained fluorinated copolymer 1 were TFE units/PMVE units/8CNVE units/C3DVE units=68.9/30.3/0.5/0.3.

[0166] Further, the filtrate after flocculation of the latex after polymerization and taking out of the fluorinated copolymer and the filtrate remaining after washing the latex, were filtered through a disc filter, and the obtained liquid was analyzed by an ion chromatography measurement device, whereby no fluoride ions were detected at a level of at least 3 mass % to the charged amount of C3DVE. Therefore, it was assumed that all the C3DVE used in charging was polymerized, and the content of C3DVE units to all units in the polymer was calculated based on the charged amount of C3DVE.

<Production of Fluorinated Copolymer Composition 1>

[0167] The fluorinated copolymer composition 1 was obtained by mixing the respective components in the ratio of 100 parts by mass of the fluorinated copolymer 1, 8 parts by mass of carbon black (manufactured by Tokai Carbon Co., Ltd., Seast 9), 3 parts by mass of tetraphenyltin (manufactured by Tokyo Chemical Industry Co., Ltd.) and 0.1 part by mass of 18-crown-6 (manufactured by FUJIFILM Wako Pure Chemical Corporation), followed by kneading with two rolls.

<Production of Crosslinked Rubber Article 1>

[0168] The fluorinated copolymer composition 1 was crosslinked and molded at 180° C. for 20 minutes to obtain a crosslinked rubber sheet of 100 mm in length×60 mm in width×1 mm in thickness (primary crosslinking). Then, under a nitrogen atmosphere, the crosslinked rubber sheet was heated at 90° C. for 3 hours, then raised to 305° C. over 5 hours, and heated for another 13 hours while maintaining 305° C. (secondary crosslinking).

[0169] The obtained crosslinked rubber sheet after secondary crosslinking was cooled to room temperature, and then punched into a No. 4 dumbbell shape as specified in JIS K6251, to obtain three test specimens of the crosslinked rubber article 1.

[Ex. 2 to Ex. 7]

[0170] Fluorinated copolymers 2 to 7, fluorinated copolymer compositions 2 to 7 and test specimens of crosslinked rubber articles 2 to 7 were obtained in the same manner as in Ex. 1, except that the types of monomers used, the addition ratio of initially added monomers, the addition ratio of post-added monomers, the order of addition of post-added monomers, the number of repetitions of the order of addition of post-added monomers, the amount of additional addition of polymerization initiator, and the polymerization conditions were changed as shown in Tables 1-1 and 1-2.

[Ex. 8]

<Production of Fluorinated Copolymer 8>

[0171] After degassing a stainless steel pressure-resistant reactor with an internal volume of 20 L equipped with anchor blades, 7.2 L of ultrapure water, 880 g of a 30 mass % solution of C.sub.2F.sub.5OCF.sub.2CF.sub.2OCF.sub.2COONH.sub.4 as an emulsifier, 17.5 g of C3DVE, and 15.9 g of a 5 mass % aqueous solution of disodium hydrogen phosphate 12 hydrate, were charged, and the gas phase was replaced with nitrogen. While stirring at a speed of 375 rpm by using the anchor blades,140 g of TFE and 631 g of PMVE were injected under pressure into the vessel, and then, the internal temperature was raised to 80° C. The reactor internal pressure was 0.90 MPa [gauge]. 40 mL of a 3 mass % aqueous solution of ammonium persulfate (APS) was added, to initiate polymerization. The added ratio of monomers to be injected under pressure before the initiation of polymerization (hereinafter referred to also as “initially added monomers”) as expressed by a molar ratio, was TFE:PMVE:C3DVE =26.7:72.4:1.0.

[0172] At the time when the reactor internal pressure dropped to 0.89 MPa [gauge] along with the progress of the polymerization, TFE was injected under pressure, and the reactor internal pressure was increased to 0.90 MPa [gauge]. This operation was repeated, and each time when 110 g of TFE was injected under pressure, 90 g of PMVE was also injected under pressure. Further, at the time when 30 g of TFE was injected under pressure, 7.0 g of 1,4-diiodoperfluorobutane was injected under pressure into the reactor from an ampoule tube, together with 50 mL of ultrapure water. When the polymerization rate started to decrease, a 3 mass % aqueous solution of APS was optionally added. The total amount of the 3 mass % aqueous solution of APS added after the initiation of polymerization was 45 mL.

[0173] Upon completion of the cycle when the total added mass of TFE became to be 990 g, 110 g of TFE was injected under pressure. At the time when the total mass of post-added TFE reached 1,100 g, the addition of the post-added monomers was stopped, and the reactor internal temperature was cooled to 10° C. to stop the polymerization reaction and to obtain a latex containing fluorinated copolymer 8. The polymerization time was 396 minutes. Further, the total added masses of the respective post-added monomers were 1,100 g of TFE and 810 g of PMVE, which can be converted to a molar ratio of TFE:PMVE=69.3:30.7.

[0174] The molar ratio of the respective units in the fluorinated copolymer 8 obtained by flocculating the latex after polymerization with a 5 mass % aqueous solution of potassium aluminum sulfate in accordance with Example 1, was TFE units:PMVE units:C3DVE units =68.5:31.2:0.3. Further, the content of iodine atoms in the fluorinated copolymer 8 was 0.20 mass %, as calculated by an apparatus combining an automatic sample combustion device as a pretreatment device for ion chromatography (manufactured by Mitsubishi Chemical Analytic Corporation, AQF-100 Model) and an ion chromatograph.

[0175] Further, the filtrate after flocculation of the latex after polymerization and taking out of the fluorinated copolymer and the filtrate remaining after washing the latex, were filtered through a disc filter, and the obtained liquid was analyzed by an ion chromatography measurement device, whereby no fluoride ions were detected at a level of at least 3 mass % to the charged amount of C3DVE. Therefore, it was assumed that all the C3DVE used in charging was polymerized, and the content of C3DVE units to all units in the polymer was calculated based on the charged amount of C3DVE.

<Production of Fluorinated Copolymer Composition 8>

[0176] The fluorinated copolymer composition 8 was obtained by mixing the respective components in the ratio of 100 parts by mass of the fluorinated copolymer 8, 15 parts by mass of carbon black (Thermax N990 manufactured by cancarb, Inc.), 3 parts by mass of triallyl isocyanurate (manufactured by Mitsubishi Chemical Corp., TAIC WH-60), 1 part by mass of 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane (manufactured by NOF Corporation, Perhexa 25B) and 1 part by mass of calcium stearate (manufactured by Kanto Chemical Co., Inc.), followed by kneading with two rolls.

<Production of Crosslinked Rubber Article 8>

[0177] With respect to the fluorinated copolymer composition 8, heat pressing (primary crosslinking) was conducted at 150° C. for 20 minutes, followed by secondary crosslinking in an oven at 250° C. for 4 hours to obtain a crosslinked rubber sheet with a thickness of 1 mm. The obtained crosslinked rubber sheet after secondary crosslinking was cooled to room temperature, and then punched into a No. 4 dumbbell shape as specified in JIS K6251, to obtain three test specimens of a crosslinked rubber article 8.

[0178] The evaluation results in the respective Ex. are shown in Table 1-1 and Table 1-2.

TABLE-US-00001 TABLE 1-1 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Ex. 8 Types of monomers used for producing fluorinated TFE TFE TFE TFE TFE TFE TFE TFE copolymer PMVE PMVE PMVE PMVE PMVE PMVE PMVE PMVE 8CNVE 8CNVE 8CNVE MV5CN 8CNVE 8CNVE 8CNVE — C3DVE C3DVE C3DVE C3DVE C6DV C3DVE — C3DVE Initially added TFE mol % 26.0 26.0 26.0 26.0 26.0 25.5 26.3 26.7 monomers PMVE mol % 72.6 72.6 72.6 72.6 72.6 71.1 73.4 72.4 8CNVE or MV5CN mol % 0.4 0.4 0.4 0.4 0.4 2.5 0.4 0 C3DVE or C6DV mol % 1.0 1.0 1.0 1.0 1.0 1.0 0 1.0 TFE g 137 137 137 137 137 137 137 140 PMVE g 635 635 635 635 635 635 635 631 8CNVE or MV5CN g 7.3 7.3 7.3 7.1 7.3 51.4 7.3 0.0 C3DVE or C6DV g 17.7 17.7 17.7 17.7 10.6 17.7 0.0 17.5 Post-added TFE mol % 74.1 74.0 74.0 74.0 74.0 74.0 74.0 69.3 monomers PMVE mol % 24.9 25.0 25.0 24.9 25.0 25.0 25.0 30.7 8CNVE or MV5CN mol % 1.0 1.1 1.1 1.1 1.0 1.1 1.1 0 C3DVE or C6DV mol % 0 0 0 0 0 0 0 0 TFE g 1193 1193 1193 1193 1193 1193 1193 1100 PMVE g 666 668 668 668 668 668 668 810 8CNVE or MV5CN g 54.8 66.7 66.7 65.9 65.7 66.7 66.2 0 C3DVE or C6DV g 0 0 0 0 0 0 0 0 Order of addition TFE.fwdarw. TFE.fwdarw. TFE.fwdarw. TFE.fwdarw. TFE.fwdarw. TFE.fwdarw. TFE.fwdarw. TFE.fwdarw. 8CNVE PMVE PMVE PMVE PMVE 8CNVE 8CNVE PMVE .fwdarw. .fwdarw. .fwdarw. .fwdarw. .fwdarw. .fwdarw. .fwdarw. PMVE 8CNVE 8CNVE MV5CN 8CNVE PMVE PMVE .fwdarw. .fwdarw. .fwdarw. 8CNVE 8CNVE 8CNVE Number of repetitions times 9 9 19 9 19 9 9 9 of the order of addition Polymerization Additionally added amount mL 51 45 50 45 50 50 35 45 initiator of APS aqueous solution Added amount of APS g 2.8 2.6 2.8 2.6 2.8 2.8 2.3 2.6 Polymerization Polymerization time min 375 387 401 390 380 465 375 396 results Solid content in latex mass % 21.0 21.18 21.5 21.2 20.9 21.3 20.05 20.54

TABLE-US-00002 TABLE 1-2 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Ex. 8 Contents of the TFE units mol % 68.9 69.0 68.7 68.6 68.8 68.7 68.9 58.5 respective units PMVE units mol % 30.3 30.2 30.5 30.6 30.5 31.0 30.2 31.2 in fluorinated 8CNVE or MV5CN units mol % 0.5 0.5 0.5 0.5 0.4 1.0 0.5 0 copolymer (molar C3DVE or C6DV units mol % 0.3 0.3 0.3 0.3 0.3 0.3 0 0.3 ratio) DVE units/CN units — 0.60 0.59 0.56 0.59 0.75 0.30 0.00 — Physical G′ kPa 456 479 482 490 482 482 437 462 properties G′.sub.0.1 kPa 535 542 547 — — 328 477 — G′.sub.1 kPa 746 746 744 — — 531 691 — Specific gravity g/cm.sup.3 2.033 2.043 2.037 2.043 2.036 2.029 2.035 2.038 M.sub.H dNm 36.0 37.7 39.1 42.7 42.0 52.7 37.0 125.0 M.sub.L dNm 22.1 21.8 21.9 19.2 21.9 14.0 17.1 14.5 M.sub.H − M.sub.L dNm 13.9 15.9 17.2 23.5 20.1 38.6 19.9 110.5 Tensile strength MPa 18.5 19.5 16.6 15.2 17.2 17.8 24.7 21.5 Tensile elongation % 159 157 143 196 155 180 198 177 100% modulus MPa 7.27 8.19 8.01 4.73 8.01 5.97 6.99 8.80 Hardness shoreA 77 79 79 71 77 73 76 73 Compression set % 63 28.8 28.7 31.0 26.2 39.8 108.1 52.0 Heat aging test Tensile strength % −43 −4.8 −2.53 −4.1 −3.2 −26.2 — — Tensile elongation % 81 19.1 34.2 20.1 29.1 28.8 — — 100% modulus % 1 0 0 1 1 −1 — — Mold release property test ◯ ◯ ◯ ◯ ◯ ◯ X X

[0179] As shown in Table 1-1 and Table 1-2, it has been confirmed that it is possible to obtain a crosslinked rubber article excellent in mold release properties, when a fluorinated copolymer having TFE units, PAVE units, DVE units and R.sub.CN units, is used (Ex. 1 to Ex. 6). Further, it has been confirmed that it is possible to make the compression set of a crosslinked rubber article smaller, when a fluorinated copolymer having a storage modulus G′ of at least 470 kPa is used (Ex. 1 to Ex. 6).

[0180] Whereas, it has been confirmed that the mold release properties of the crosslinked rubber article are insufficient when a fluorinated copolymer not having DVE units or R.sub.CN units is used (Ex. 7 and Ex. 8). Further, with respect to the crosslinked rubber obtained by using the fluorinated copolymer not having DVE units or R.sub.CN units, the test specimen underwent deformation, when it was heated to 300° C. for the heat aging test, and thus it was not possible to measure the tensile strength, 100% modulus, and tensile elongation.

[0181] This application is a continuation of PCT Application No. PCT/JP2020/040280, filed on Oct. 27, 2020, which is based upon and claims the benefit of priority from Japanese Patent Application No. 2019-197115 filed on Oct. 30, 2019. The contents of those applications are incorporated herein by reference in their entireties.