Method for decomposing fluorine-containing polymers

Abstract

To provide a method for decomposing a fluorine-containing polymer that is capable of decomposing the fluorine-containing polymer while suppressing impurity formation following the decomposition reaction.SOLUTION: A method for decomposing a fluorine-containing polymer comprises a decomposition step of reacting the fluorine-containing polymer in subcritical water at a temperature of 180°C or more and less than 250°C, with a concentration of 0.5 M or less of at least one basic compound selected from alkali metal hydroxides and alkaline earth metal hydroxides.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This disclosure relates to a method for decomposing fluorine-containing polymers. [Background technology]

[0002] Due to their high chemical stability and heat resistance, fluorine-containing polymers require high temperatures for incineration in waste treatment, and the hydrogen fluoride produced significantly degrades the incinerator material. Therefore, there is a need for new waste treatment methods that are neither incineration nor landfill. For example, Patent Documents 1 and 2 and Non-Patent Document 1 describe a method of decomposing fluorine-containing polymers by reacting them in subcritical water containing basic compounds such as potassium hydroxide. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2021-155478 [Patent Document 2] Japanese Patent Publication No. 2023-066742 [Non-patent literature]

[0004] [Non-Patent Document 1] Jin Hamaura et al., Eur. Polym. J. 182 (2023), 111724 [Overview of the project] [Problems that the invention aims to solve]

[0005] The purpose of this disclosure is to provide a method for decomposing fluorine-containing polymers that can decompose fluorine-containing polymers while suppressing the generation of impurities after the decomposition reaction. [Means for solving the problem]

[0006] (1) of this disclosure relates to a method for decomposing a fluorine-containing polymer, which includes a decomposition step of reacting the fluorine-containing polymer in subcritical water at a temperature of 180°C or higher and less than 250°C, in which the concentration of at least one basic compound selected from the group consisting of alkali metal hydroxides and alkaline earth metal hydroxides is 0.5 M or less.

[0007] Disclosure (2) is a method for decomposing a fluorine-containing polymer according to Disclosure (1), wherein the temperature of the subcritical water in the decomposition step is 200°C or higher.

[0008] Disclosure (3) is a method for decomposing the fluorine-containing polymer of Disclosure (1) or (2), wherein the fluorine-containing polymer is fluororubber.

[0009] This disclosure (4) is a method for decomposing a fluorine-containing polymer according to this disclosure (3), wherein the object to be decomposed in the above decomposition step is a crosslinked body of the composition containing the above-mentioned fluororubber.

[0010] Disclosure (5) is a method for decomposing a fluorine-containing polymer in any combination of any of Disclosures (1) to (4), which includes a grinding step of grinding the fluorine-containing polymer into pulverized particles having a maximum straight length of 3 mm or less, prior to the decomposition step.

[0011] Disclosure (6) is a method for decomposing a fluorine-containing polymer in any combination of the basic compound described in Disclosures (1) to (5), wherein the basic compound is sodium hydroxide and / or potassium hydroxide.

[0012] Disclosure (7) is a method for decomposing a fluorine-containing polymer in any combination of any of Disclosures (1) to (6), which includes a recovery step in which calcium hydroxide is added to the aqueous solution after decomposition to recover the generated calcium fluoride. [Effects of the Invention]

[0013] According to this disclosure, it is possible to provide a method for decomposing fluorine-containing polymers that can decompose fluorine-containing polymers while suppressing the generation of impurities after the decomposition reaction. [Modes for carrying out the invention]

[0014] The following provides a detailed explanation of this disclosure.

[0015] This disclosure relates to a method for decomposing a fluorine-containing polymer, which includes a decomposition step of reacting the fluorine-containing polymer in subcritical water at a temperature of 180°C or higher and less than 250°C, in which the concentration of at least one basic compound selected from the group consisting of alkali metal hydroxides and alkaline earth metal hydroxides is 0.5 M or less. Because the method for decomposing a fluorine-containing polymer according to this disclosure has the above configuration, it is possible to decompose the fluorine-containing polymer while suppressing the generation of impurities after the decomposition reaction.

[0016] In this disclosure, a fluorine-containing polymer is treated in subcritical water containing a basic compound. It is believed that the polymer decomposition occurs when hydrogen fluoride (HF) is extracted from the polymer by the basic compound. According to this mechanism, decomposition by this disclosure is difficult for polymers without hydrogen atoms, such as polytetrafluoroethylene (PTFE). Therefore, it is preferable that polymers without hydrogen atoms be excluded from this disclosure.

[0017] Furthermore, in this disclosure, as described above, decomposition is considered to occur by the extraction of HF from the polymer, and although fluorine atoms are removed from the polymer, the polymer is not completely decomposed into carbon dioxide. However, since the removal of fluorine atoms from the polymer is achieved, in this disclosure, even decomposition that does not completely decompose into carbon dioxide is treated as decomposition of the polymer.

[0018] Subcritical water is liquid water that, under pressure, is in a temperature range above 100°C but below its critical temperature of 374°C. Subcritical water has different physical properties from water below 100°C, and in particular, subcritical water in the range of 200°C to 300°C has a significantly reduced dielectric constant, exhibiting lipid solubility almost equivalent to methanol or acetone at room temperature, and 10°C at room temperature. -14The ion product was mol / L, but it was 10 -11 The concentrations of hydrogen ions and hydroxide ions reach the order of mol / L, and can be up to 30 times higher than that of water at room temperature. For this reason, it is known that subcritical water, especially at 200°C to 300°C, exhibits different reactivity than water at room temperature. In the decomposition method of this disclosure, the temperature of the subcritical water in the decomposition step is preferably less than 250°C, preferably 245°C or lower, more preferably 240°C or lower, even more preferably 235°C or lower, and also preferably 180°C or higher, preferably 200°C or higher, more preferably 205°C or higher, even more preferably 210°C or higher, even more preferably 215°C or higher, particularly preferably 220°C or higher, and especially preferably 225°C or higher.

[0019] The water used in preparing subcritical water is not particularly limited; any type of water may be used, such as tap water, deionized water, distilled water, or well water. However, deionized water or distilled water is preferred from the viewpoint of suppressing side reactions caused by coexisting salts, etc. The amount of water used should be enough to sufficiently immerse the fluorine-containing polymer to be treated. However, care must be taken because if the amount of water introduced into the sealed container for pressurization is extremely small, it will all turn into steam after heating and will not become subcritical water.

[0020] The decomposition method of this disclosure uses at least one basic compound selected from the group consisting of alkali metal hydroxides and alkaline earth metal hydroxides. As previously stated, the basic compound is used to cause a reaction in which HF is abstracted from the fluorine-containing polymer.

[0021] Examples of alkali metal hydroxides include lithium hydroxide, sodium hydroxide, potassium hydroxide, and cesium hydroxide, among which sodium hydroxide and / or potassium hydroxide are preferred. Potassium hydroxide is known to have higher activity and higher basicity than sodium hydroxide in concentrated solutions, and is expected to have high activity in the abstraction reaction of HF. In fact, in this disclosure, it has been confirmed that the decomposition of fluorine-containing polymers using potassium hydroxide is more active than when sodium hydroxide is used. From this viewpoint, potassium hydroxide is the most preferred.

[0022] Examples of alkaline earth metal hydroxides include calcium hydroxide and barium hydroxide.

[0023] The concentration of the basic compound in the above subcritical water is 0.5 M or less, preferably 0.45 M or less, more preferably 0.40 M or less, even more preferably 0.35 M or less, preferably 0.01 M or more, more preferably 0.05 M or more, even more preferably 0.10 M or more, and even more preferably 0.15 M or more. As is well known to those skilled in the art, the unit "M" means mol / L.

[0024] The pH of the subcritical water described above is preferably 12 or higher, more preferably 12.7 or higher, even more preferably 13 or higher, and also preferably 13.7 or lower, more preferably 13.6 or lower, and even more preferably 13.5 or lower.

[0025] Next, a method for reacting a fluorine-containing polymer in subcritical water containing a basic compound will be described. Water, a basic compound, and the fluorine-containing polymer to be treated are added to a pressure vessel of a size appropriate to the amount of fluorine-containing polymer to be treated, and the inside of the pressure vessel is pressurized and sealed. To pressurize the inside of the pressure vessel, a gas can be sealed inside. Examples of such gases include air, argon, and nitrogen. The degree of pressurization can be around 0.5 MPa, but is not particularly limited.

[0026] The pressure vessel that has undergone the above process is heated to initiate the decomposition reaction. The heating temperature is less than 250°C, but is preferably 245°C or lower, more preferably 240°C or lower, even more preferably 235°C or lower, and also 180°C or higher, preferably 200°C or higher, more preferably 205°C or higher, even more preferably 210°C or higher, even more preferably 215°C or higher, particularly preferably 220°C or higher, and especially preferably 225°C or higher. If the pressure vessel itself is equipped with a heating means, it may be heated using that heating means; if the pressure vessel itself is not equipped with a heating means, the entire pressure vessel may be heated in an autoclave or oven. The reaction time can be approximately 6 to 24 hours.

[0027] The aqueous solution after the decomposition reaction contains fluorine atoms that were contained in the fluorine-containing polymer as fluoride ions. The decomposition method of this disclosure preferably includes a recovery step after the decomposition step, in which calcium hydroxide is added to the aqueous solution after decomposition and the generated calcium fluoride is recovered. The fluoride ions contained in the aqueous solution after decomposition can be converted into calcium fluoride, which can be used as a raw material for any fluorine compound, by reacting with calcium ions generated from the added calcium hydroxide. The decomposition method of this disclosure, by including the recovery step, makes it possible to make effective use of resources. Furthermore, as described above, the decomposition method of fluorine-containing polymer of this disclosure can suppress the generation of impurities after the decomposition reaction, and therefore the amount of impurities when recovering calcium fluoride can also be reduced.

[0028] Furthermore, the aqueous solution remaining after the decomposition reaction contains not only fluoride ions but also polymer decomposition products remaining after HF has been abstracted. As already mentioned, these decomposition products are thought to be elemental carbon with double bonds and often appear black. Since they are solids, they can be easily separated, and because the fluorine atoms have been removed by the recovery process described above, they can also be easily disposed of by incineration.

[0029] The decomposition method of this disclosure preferably includes a grinding step before the above decomposition step, in which the fluorine-containing polymer is ground into pulverized particles with a maximum straight length of 3 mm or less. Including the above grinding step in the decomposition method of this disclosure makes it easier to decompose the fluorine-containing polymer.

[0030] While there are no particular limitations on the grinding method, examples include freeze grinding, disc milling, hammer milling, stone mill type grinding, and jet milling.

[0031] The grinding temperature is preferably -200°C or higher, and more preferably 90°C or lower. More preferably 40°C or lower, and even more preferably 0°C or lower.

[0032] The maximum linear length of the pulverized particles of the fluorine-containing polymer is preferably 3 mm or less, more preferably 2 mm or less, even more preferably 1 mm or less, and especially preferably 500 μm or less. Furthermore, it is preferably 10 μm or more, more preferably 30 μm or more, and even more preferably 100 μm or more. When the average particle size of the pulverized particles of the fluorine-containing polymer is within the above range, the fluorine-containing polymer becomes even easier to decompose.

[0033] The maximum straight line length mentioned above was determined by observing over 100 secondary particles using SEM imaging and measuring the major axis of each secondary particle. The largest major axis among these was defined as the maximum straight line length.

[0034] The transmittance of the aqueous solution after the decomposition reaction can be measured using an Agilent Cary 7000 UMS. The transmittance was defined as the average value of %T in the 380-780 nm range. A higher transmittance value indicates a lighter solution color and fewer impurities.

[0035] The transmittance of the aqueous solution after the above decomposition reaction is preferably 40%T or higher, more preferably 50%T or higher, and even more preferably 70%T or higher. There is no particular upper limit, and it may be 100%T, but it is usually around 90%T. If the transmittance of the aqueous solution after the above decomposition reaction is within the above range, calcium hydroxide can be added to the aqueous solution after the decomposition step to reduce the amount of impurities contained in the produced calcium fluoride.

[0036] The fluorine-containing polymers targeted for decomposition in this disclosure are polymers containing fluorine atoms in their molecules; any polymer containing even one fluorine atom in its molecule is subject to decomposition in this disclosure. Fluorine-containing polymers are valued for their high chemical resistance, heat resistance, weather resistance, and other properties, and are used in a wide range of applications, including industry and medicine. On the other hand, these polymers are not easily decomposed, which is a consequence of their high chemical stability and heat resistance. This disclosure provides a method for chemically decomposing these polymers. Preferably, such fluorine-containing polymers have hydrogen atoms in their molecules. Furthermore, the fluorine-containing polymer may be a fluororesin or a fluororubber, and may be a homopolymer or a copolymer.

[0037] Examples of the above-mentioned fluororesins include polytetrafluoroethylene [PTFE], tetrafluoroethylene [TFE] / perfluoro(alkyl vinyl ether) [PAVE] copolymer [PFA], TFE / hexafluoropropylene [HFP] copolymer [FEP], ethylene [Et] / TFE copolymer [ETFE], Et / TFE / HFP copolymer [EFEP], polychlorotrifluoroethylene [PCTFE], chlorotrifluoroethylene [CTFE] / TFE copolymer, CTFE / TFE / PAVE copolymer, Et / CTFE copolymer, polyvinyl fluoride [PVF], polyvinylidene fluoride [PVdF], vinylidene fluoride [VdF] / TFE copolymer, VdF / HFP copolymer, VdF / TFE / HFP copolymer, VdF / HFP / (meth)acrylic acid copolymer, VdF / CTFE copolymer, VdF / pentafluoropropylene copolymer, VdF / PAVE / TFE copolymer, TFE / perfluoroalkylallyl ether copolymer, and the like. The above perfluoroalkyl allyl ether is CF2=CFCF2-O-Rf 4 (Rf 4 It is a monomer represented by a perfluoroalkyl group having 1 to 5 carbon atoms.

[0038] The above-mentioned fluororesins include partially fluorinated polymers and perfluoropolymers, but partially fluorinated polymers are preferred.

[0039] Among the above fluororesins, at least one selected from the group consisting of ETFE, EFEP, Et / CTFE copolymer, PVF, PVdF, VdF / TFE copolymer, VdF / HFP copolymer, VdF / TFE / HFP copolymer, VdF / HFP / (meth)acrylic acid copolymer, VdF / CTFE copolymer, VdF / pentafluoropropylene copolymer, and VdF / PAVE / TFE copolymer is preferred, with VdF / HFP copolymer and VdF / TFE / HFP copolymer being more preferred.

[0040] In the above PAVE, the number of carbon atoms in the perfluoroalkyl group is preferably 1 to 10, and more preferably 1 to 5. Examples of perfluoroalkyl groups include perfluoromethyl, perfluoroethyl, perfluoropropyl, perfluorobutyl, perfluoropentyl, and perfluorohexyl groups, but perfluoro(propyl vinyl ether) [PPVE] in which the perfluoroalkyl group is a perfluoropropyl group is preferred.

[0041] Examples of the above-mentioned fluororubbers include partially fluorinated rubber and perfluororubber, but partially fluorinated rubber is preferred.

[0042] Examples of the partially fluorinated rubbers mentioned above include vinylidene fluoride (VdF)-based fluororubber, tetrafluoroethylene (TFE) / propylene (Pr)-based fluororubber, tetrafluoroethylene (TFE) / propylene / vinylidene fluoride (VdF)-based fluororubber, ethylene / hexafluoropropylene (HFP)-based fluororubber, ethylene / hexafluoropropylene (HFP) / vinylidene fluoride (VdF)-based fluororubber, and ethylene / hexafluoropropylene (HFP) / tetrafluoroethylene (TFE)-based fluororubber. Among these, it is preferable that at least one is selected from the group consisting of vinylidene fluoride-based fluororubber and tetrafluoroethylene / propylene-based fluororubber.

[0043] The above vinylidene fluoride-based fluororubber is preferably a copolymer consisting of 45 to 85 mol% vinylidene fluoride and 55 to 15 mol% of at least one other monomer copolymerizable with vinylidene fluoride. Preferably, it is a copolymer consisting of 50 to 80 mol% vinylidene fluoride and 50 to 20 mol% of at least one other monomer copolymerizable with vinylidene fluoride.

[0044] In the present specification, the content of each monomer constituting the fluoropolymer can be calculated by appropriately combining NMR, FT-IR, elemental analysis, and X-ray fluorescence analysis depending on the type of monomer.

[0045] Examples of the at least one other monomer copolymerizable with the vinylidene fluoride include tetrafluoroethylene [TFE], hexafluoropropylene [HFP], fluoroalkyl vinyl ether, trifluoroethylene, trifluoropropylene, pentafluoropropylene, trifluorobutene, tetrafluoroisobutene, hexafluoroisobutene, vinyl fluoride, perfluoroalkyl allyl ether, and general formula (6): CH2=CFRf 61 (wherein Rf 61 is a linear or branched fluoroalkyl group having 1 to 12 carbon atoms), a fluoromonomer represented by general formula (7): CH2=CH-(CF2) n -X 2 (wherein X 2 is H or F, and n is an integer of 3 to 10), monomers such as monomers that give crosslinking sites; and non-fluorinated monomers such as ethylene, propylene, and alkyl vinyl ether. These can be used each alone or in any arbitrary combination. Among these, it is preferable to use at least one selected from the group consisting of TFE, HFP, and fluoroalkyl vinyl ether. As the fluoroalkyl vinyl ether, general formula (8): CF2=CF-ORf 81 (wherein Rf 81 represents a perfluoroalkyl group having 1 to 8 carbon atoms), a fluoromonomer represented by general formula (9): CF2=CFOCF2ORf 91 (wherein Rf 91 is a linear or branched perfluoroalkyl group having 1 to 6 carbon atoms, a cyclic perfluoroalkyl group having 5 to 6 carbon atoms, or a linear or branched perfluorooxyalkyl group having 2 to 6 carbon atoms and containing 1 to 3 oxygen atoms), and a fluoromonomer represented by General formula (10): CF2=CFO(CF2CF(Y 10 )O) m (CF2) n F (In the formula, Y 10 represents a fluorine atom or a trifluoromethyl group. m is an integer from 1 to 4. n is an integer from 1 to 4. Preferably, it is at least one selected from the group consisting of fluoromonomers represented by ), and more preferably a fluoromonomer represented by general formula (8). The above perfluoroalkylallyl ethers include: General formula (11): CF2=CF-CF2ORf 111 (In the formula, Rf 111 represents a perfluoroalkyl group having 1 to 5 carbon atoms. Fluoromonomers represented by ) are preferred.

[0046] Specific examples of vinylidene fluoride-based fluororubbers include VdF / HFP rubber, VdF / HFP / TFE rubber, VdF / fluoromonomer rubber represented by general formula (6), VdF / fluoromonomer / TFE rubber represented by general formula (6), VdF / perfluoro(methyl vinyl ether) [PMVE] rubber, VdF / PMVE / TFE rubber, and VdF / PMVE / TFE / HFP rubber. Among the fluoromonomer rubber represented by VdF / general formula (6), VdF / CH2=CFCF3 rubber is preferred, and among the fluoromonomer / TFE rubber represented by VdF / general formula (6), VdF / TFE / CH2=CFCF3 rubber is preferred.

[0047] The above VdF / CH2=CFCF3 rubber is preferably a copolymer consisting of 40 to 99.5 mol% VdF and 30.5 to 60 mol% CH2=CFCF, and more preferably a copolymer consisting of 50 to 85 mol% VdF and 320 to 50 mol% CH2=CFCF.

[0048] The above-mentioned tetrafluoroethylene / propylene-based fluororubber is preferably a copolymer consisting of 45-70 mol% tetrafluoroethylene, 55-30 mol% propylene, and 0-5 mol% fluoromonomer that provides the crosslinking sites.

[0049] A monomer that provides crosslinking sites is a monomer (curation site monomer) that has crosslinkable groups that provide crosslinking sites to a fluoropolymer for crosslinking by a crosslinking agent.

[0050] As monomers that provide crosslinking sites, General formula (12):CX 3 2=CX 3 -R f 121 CHR 121 X 4 (In the formula, X 3 is a hydrogen atom, a fluorine atom, or CH3, R f 121 is a fluoroalkylene group, a perfluoroalkylene group, a fluoro(poly)oxyalkylene group or a perfluoro(poly)oxyalkylene group, R 121 is a hydrogen atom or CH3, X 4 Fluoromers represented by an iodine atom or a bromine atom, General formula (13):CX 3 2=CX 3 -R f 131 X 4 (In the formula, X 3 is a hydrogen atom, a fluorine atom, or CH3, R f 131 X is a fluoroalkylene group, a perfluoroalkylene group, a fluoropolyoxyalkylene group, or a perfluoropolyoxyalkylene group. 4 Fluoromers represented by an iodine atom or a bromine atom, General formula (14): CF2=CFO(CF2CF(CF3)O) m (CF2) n -X 5 (In the formula, m is an integer from 0 to 5, n is an integer from 1 to 3, X5 Fluoromers represented by a cyano group, a carboxyl group, an alkoxycarbonyl group, an iodine atom, a bromine atom, or -CH2I, General formula (15): CH2=CFCF2O(CF(CF3)CF2O) m (CF(CF3)) n -X 6 (In the formula, m is an integer from 0 to 5, n is an integer from 1 to 3, X 6 (where is a cyano group, a carboxyl group, an alkoxycarbonyl group, an iodine atom, a bromine atom, or -CH2OH) and, General formula (16):CR 162 R 163 =CR 164 -Z-CR 165 =CR 166 R 167 (In the formula, R 162 , R 163 , R 164 , R 165 , R 166 and R 167 , are the same or different hydrogen atoms or C1-C5 alkyl groups. Z is a linear or branched alkylene group having C1-C18, a cycloalkylene group having C3-C18, a C1-C10 alkylene group or oxyalkylene group having at least partially fluorinated, or , -(Q) p -CF2O-(CF2CF2O) m (CF2O) n -CF2-(Q) p - It is preferable that the monomer is at least one selected from the group consisting of monomers represented by (wherein Q is an alkylene group or an oxyalkylene group, p is 0 or 1, and m / n is 0.2 to 5) and has a molecular weight of 500 to 10000.

[0051] X 3 It is preferably a fluorine atom. f 121 and Rf 131 It is preferable that it is a perfluoroalkylene group having 1 to 5 carbon atoms. 121 It is preferably a hydrogen atom. 5 It is preferable that this is a cyano group, an alkoxycarbonyl group, an iodine atom, a bromine atom, or -CH2I. 6 It is preferable that the component is a cyano group, an alkoxycarbonyl group, an iodine atom, a bromine atom, or -CH2OH.

[0052] The monomers that provide the crosslinking site are CF2=CFOCF2CF(CF3)OCF2CF2CN, CF2=CFOCF2CF(CF3)OCF2CF2COOH, CF2=CFOCF2CF(CF3)OCF2CF2CH2I, CF2=CFOCF2CF2CH2I, CH2=CFCF2OCF(CF3)CF2OCF(CF3)CN, CH2=CFCF2OCF(CF3)CF2OCF(CF3)COOH, CH2=CFCF2OCF( It is preferable that it is at least one selected from the group consisting of CF3)CF2OCF(CF3)CH2OH, CH2=CHCF2CF2I, CH2=CH(CF2)2CH=CH2, CH2=CH(CF2)6CH=CH2, and CF2=CFO(CF2)5CN, and more preferably at least one selected from the group consisting of CF2=CFOCF2CF(CF3)OCF2CF2CN and CF2=CFOCF2CF2CH2I.

[0053] The above-mentioned fluororubber is preferably such that its glass transition temperature is -70°C or higher, more preferably -60°C or higher, and even more preferably -50°C or higher, in order to have excellent compression set characteristics at high temperatures. Furthermore, in order to have good cold resistance, it is preferably such that its glass transition temperature is 5°C or lower, more preferably 0°C or lower, and even more preferably -3°C or lower.

[0054] The above glass transition temperature can be determined by using a differential scanning calorimeter (Mettler-Toledo, DSC822e) to obtain a DSC curve by heating 10 mg of the sample at 10°C / min, and then finding the temperature at the midpoint of the intersection of the extension of the baseline before and after the second-order transition of the DSC curve and the tangent line at the inflection point of the DSC curve.

[0055] The above-mentioned fluororubber has good heat resistance, and its Mooney viscosity at 170°C is ML. (1+20) It is preferable that the ratio is 30 or more, more preferably 40 or more, and even more preferably 50 or more. Furthermore, in terms of good processability, it is preferable that the ratio is 150 or less, more preferably 120 or less, and even more preferably 110 or less.

[0056] The above-mentioned fluororubber has good heat resistance, and its Mooney viscosity at 140°C is ML. (1+20) It is preferable that the ratio is 30 or more, more preferably 40 or more, and even more preferably 50 or more. Furthermore, in terms of good processability, it is preferable that the ratio is 180 or less, more preferably 150 or less, and even more preferably 110 or less.

[0057] The above-mentioned fluororubber has good heat resistance, and its Mooney viscosity at 100°C is ML. (1+10) It is preferable that the ratio be 10 or more, more preferably 20 or more, and even more preferably 30 or more. Furthermore, in terms of good processability, it is preferable that the ratio be 120 or less, more preferably 100 or less, and even more preferably 80 or less.

[0058] The above Mooney viscosity can be measured using an ALPHA TECHNOLOGIES MV2000E Mooney viscometer at 170°C, 140°C, or 100°C, in accordance with JIS K6300.

[0059] In the decomposition method of this disclosure, the object to be decomposed in the decomposition step may be a crosslinked body of the composition containing the fluororubber. Preferably, the composition contains the fluororubber and a crosslinking agent.

[0060] Examples of the above crosslinking agents include those used in peroxide crosslinking, polyol crosslinking, polyamine crosslinking, triazine crosslinking, oxazole crosslinking, imidazole crosslinking, and thiazole crosslinking. When the above fluororubber is a fluororubber having a cyano group (-CN group), at least one selected from the group consisting of oxazole crosslinking agents, imidazole crosslinking agents, and thiazole crosslinking agents is preferred as the above crosslinking agent.

[0061] The crosslinking agent used in peroxide crosslinking can be any organic peroxide that can readily generate peroxy radicals in the presence of heat or an oxidation-reduction system. Specifically, for example, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane can be used. Generally, the type and amount of organic peroxide used are selected considering the amount of active -OO-, the decomposition temperature, etc.

[0062] Furthermore, any crosslinking aid that can be used in this case is a compound that has reactive activity with respect to peroxy radicals and polymer radicals, and examples include polyfunctional compounds having functional groups such as -CH=CH2, -CH2CH=CH2, -CF=CF2, -C(CF3)=CF2, -C(CH3)=CF2, -CF=CF(CF3), -CF=CF(CH3), -C(C6H5)=CF2, -CF=CF(C6H5), -CH=CF2, -CF=CHF, -C(CF3)=CHF, -CF=CH(CF3), and -CH=CF(CF3) (where "C6H5" represents a phenyl group). Specifically, examples include triallyl cyanurate, triallyl isocyanurate (TAIC), triacryl formal, triallyl trimellitate, N,N'-n-phenylene bismaleimide, dipropagyl terephthalate, diallyl phthalate, tetraallyl terephthalate amide, triallyl phosphate, bismaleimide, fluorinated triallyl isocyanurate (1,3,5-tris(2,3,3-trifluoro-2-propenyl)-1,3,5-triazine 2,4,6-trione), tris(diallylamine)-S-triazine, triallyl phosphite, N,N-diallylcrylamide, 1,6-divindodecafluorohexane, and the like.

[0063] Furthermore, as a crosslinking aid used with peroxide crosslinking agents, general formula (48): [ka] (In the formula, there are six R 31 Each of these is an independently selected halogenated group having 1 to 5 carbon atoms, which may contain H, a halogen atom, or an ether bond, and Z 31 This can also include compounds represented by a linear or branched alkylene group, cycloalkylene group, or (per)fluoropolyoxyalkylene group having 1 to 18 carbon atoms, which optionally contains a heteroatom.

[0064] Compounds represented by general formula (48) include general formula (49):

Chemical Formula

Chemical Formula

Chemical Formula

[0065] Examples of the crosslinking agent or the crosslinking assistant used together with the peroxide crosslinking agent include those represented by general formula (52):

Chemical Formula

[0066] Examples of the compound having the structure represented by General Formula (52) include General Formula (53):

Chemical Formula

[0067] (wherein R 35 to R 37 are as defined above. p is an integer of 0 to 2, and n is an integer of 2 to 6.), and General Formula (54):

Chemical Formula

[0068] The heteroatom-containing group is not particularly limited as long as it is a divalent group containing a heteroatom. Examples of the heteroatom include an oxygen atom, a nitrogen atom, a sulfur atom, a boron atom, and a phosphorus atom.

[0069] Examples of crosslinking agents used for polyol crosslinking include polyhydric alcohol compounds such as bisphenol A and bisphenol AF.

[0070] Examples of crosslinking agents used for polyamine crosslinking include polyhydric amine compounds such as hexamethylenediamine carbamate, N,N'-disinnamyridene-1,6-hexanediamine, and 4,4'-bis(aminocyclohexyl)methanecarbamate.

[0071] Examples of crosslinking agents used in oxazole crosslinking, imidazole crosslinking, and thiazole crosslinking include those of general formula (55):

[0072] [ka] (In the formula, R 41 -SO2-, -O-, -CO-, alkylene groups with 1 to 6 carbon atoms, perfluoroalkylene groups with 1 to 10 carbon atoms, or single bonds,

[0073] [ka]

[0074] The group is represented by R 42 and R 43 One side is -NH2 and the other is -NHR 44 , -NH2, -OH or -SH, R 44 is a hydrogen atom, a fluorine atom, or a monovalent organic group, preferably R 42 is -NH2 and R 43 ga-NHR 44 Examples of crosslinking agents that can be represented as follows: bisdiaminophenyl-based crosslinking agents, bisaminophenol-based crosslinking agents, and bisaminothiophenol-based crosslinking agents.

[0075] Preferred specific examples of alkylene groups having 1 to 6 carbon atoms include methylene, ethylene, propylene, butylene, pentylene, and hexylene groups, while perfluoroalkylene groups having 1 to 10 carbon atoms include... [ka] These are some examples.

[0076] These compounds are known as examples of bisdiaminophenyl compounds in Japanese Patent Publication No. 2-59177, Japanese Patent Application Publication No. 8-120146, and others.

[0077] For crosslinking agents used in oxazole crosslinking, imidazole crosslinking, and thiazole crosslinking, also, general formula (56): [ka] (In the formula, R 41 As mentioned above, R 45 Each of these is independently one of the following bases: [ka] A bisamido-razone crosslinking agent represented by the general formula (57): [ka] (In the formula, Rf 41 Amidorazone crosslinking agent represented by the general formula (58): (where is a perfluoroalkylene group having 1 to 10 carbon atoms) [ka] Bisamido oxime crosslinking agents represented by the formula (where n is an integer from 1 to 10), general formula (59): HN=CR 45 R 46 (In the formula, R 45 These are H, NH2, and NHR 47 Selected from the group consisting of R 46 Ph, SO2H, NR 48 R 49 Selected from the group consisting of , 2-pyridine, and CH2CONH2, R 47 It is selected from the group consisting of Ph, NH2, and CN, and R 48is selected from the group consisting of H, NHPh, CH2CONH2, linear alkyl groups having 1 to 8 carbon atoms, and branched alkyl groups having 1 to 8 carbon atoms, and R 49 Ph, COOC(CH3)3, NH2, CH2COOH, CSNH2, CNHNH3 + Cl - p-phenylCN, [ka] Other examples include compounds represented by (selected from the group consisting of COPh).

[0078] These bisaminophenol-based crosslinking agents, bisaminothiophenol-based crosslinking agents, and bisdiaminophenyl-based crosslinking agents have conventionally been used in crosslinking systems that use cyano groups as crosslinking sites. However, they also react with carboxyl groups and alkoxycarbonyl groups to form oxazole rings, thiazole rings, and imidazole rings, giving crosslinked products.

[0079] Furthermore, the above crosslinking agent is the general formula (60):X 41 -(CH2) n -R 50 -(CH2) m -X 41 (In the formula, X 41 Each of these independently comprises an alkyne group, a nitrile group, or Y 41 P N3(Y 41 (where is SO, SO2, C6H4 or CO, and p is 0 or 1), n ​​and m are independent integers from 1 to 4, and R 50 teeth, i) Fluoroalkylene group having 3 to 10 carbon atoms, ii) Fluoroalkoxylene groups having 3 to 10 carbon atoms, iii) Substituted arylene group, iv) Oligomers containing copolymer units of vinylidene fluoride and perfluoro(methyl vinyl ether), v) Oligomers containing copolymer units of vinylidene fluoride and hexafluoropropylene, vi) Oligomers containing copolymer units of tetrafluoroethylene and perfluoro(methyl vinyl ether), vii) A crosslinking agent may also be cited, which is selected from the group consisting of oligomers containing copolymer units of tetrafluoroethylene and hydrocarbon olefins. This crosslinking agent is preferably used together with fluororubber having a nitrile group, an azide group, a sulfonyl azide group, a carbonyl azide group, or an alkyne group. For example, the nitrile group of the fluororubber reacts with the azide group of the crosslinking agent to form a tetrazole ring and give a crosslinked product.

[0080] Particularly preferred crosslinking agents include compounds having multiple 3-amino-4-hydroxyphenyl groups or 3-amino-4-mercaptophenyl groups, or general formula (61):

[0081] [ka]

[0082] (In the formula, R 41 , R 42 and R 43Examples of compounds represented as above include, specifically, 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (generic name: bis(aminophenol)AF), 2,2-bis(3-amino-4-mercaptophenyl)hexafluoropropane, tetraaminobenzene, bis-3,4-diaminophenylmethane, bis-3,4-diaminophenyl ether, 2,2-bis(3,4-diaminophenyl)hexafluoropropane, 2,2-bis[3-amino-4-(N-phenylamino)pheni Examples include 2,2-bis[3-amino-4-(N-methylamino)phenyl]hexafluoropropane, 2,2-bis[3-amino-4-(N-ethylamino)phenyl]hexafluoropropane, 2,2-bis[3-amino-4-(N-propylamino)phenyl]hexafluoropropane, 2,2-bis[3-amino-4-(N-perfluorophenylamino)phenyl]hexafluoropropane, and 2,2-bis[3-amino-4-(N-benzylamino)phenyl]hexafluoropropane.

[0083] Among these, 2,2-bis[3-amino-4-(N-phenylamino)phenyl]hexafluoropropane is preferred as the crosslinking agent due to its heat resistance, steam resistance, amine resistance, and good crosslinking properties.

[0084] The amount of the crosslinking agent is preferably 0.01 to 10 parts by mass, and more preferably 0.05 to 5 parts by mass, per 100 parts by mass of fluororubber.

[0085] The above composition may contain a general filler.

[0086] Examples of the above-mentioned general fillers include imide-based fillers having an imide structure such as polyimide, polyamideimide, and polyetherimide; organic fillers made of engineering plastics such as polyarylate, polysulfone, polyethersulfone, polyphenylene sulfide, polyetheretherketone, polyoxybenzoate, and other polyoxybenzoates; metal oxide fillers such as aluminum oxide, silicon oxide, and yttrium oxide; metal carbides such as silicon carbide and aluminum carbide; metal nitride fillers such as silicon nitride and aluminum nitride; and inorganic fillers such as aluminum fluoride, carbon fluoride, and carbon black.

[0087] Among these, aluminum oxide, yttrium oxide, silicon oxide, polyimide, carbon fluoride, silicon carbide, silicon nitride, aluminum nitride, and carbon black are preferred.

[0088] Furthermore, the inorganic fillers and organic fillers mentioned above may be used individually or in combination of two or more types.

[0089] The amount of the above-mentioned general filler added is preferably 0.5 to 100 parts by mass, more preferably 5 to 50 parts by mass, per 100 parts by mass of fluororubber.

[0090] In fields where high purity and non-contamination are not particularly required, conventional additives used in fluorine-containing polymer compositions, such as fillers, processing aids, plasticizers, and colorants, may be added as needed. One or more commonly used crosslinking agents or crosslinking aids different from those mentioned above may also be added.

[0091] The above composition can be manufactured by kneading the above fluororubber, the above crosslinking agent, and optionally the above crosslinking accelerator and filler.

[0092] The above mixing can be carried out using conventional polymer processing machinery, such as open rolls, Banbury mixers, kneaders, and closed-type mixers.

[0093] The above-mentioned crosslinked material can be manufactured by molding the above-mentioned composition and crosslinking the resulting molded product, or by performing molding and crosslinking simultaneously.

[0094] The molding method is not particularly limited and includes, for example, compression molding, extrusion molding, transfer molding, injection molding, etc.

[0095] The crosslinking conditions are preferably determined by the type of crosslinking agent used. For example, crosslinking is preferably carried out at a temperature of 140 to 300°C for 1 minute to 24 hours. Crosslinking can also be carried out under normal pressure, pressurized pressure, reduced pressure, or in air.

[0096] The crosslinking method is not particularly limited and can be steam crosslinking, pressure molding, or a conventional method in which the crosslinking reaction is initiated by heating. Radiation crosslinking at room temperature and pressure is also acceptable.

[0097] While the initial cross-linking process (called primary cross-linking) alone may suffice, a post-processing step called secondary cross-linking may be performed after primary cross-linking.

[0098] When performing primary and secondary crosslinking, primary crosslinking is preferably carried out at 150-250°C for 5-120 minutes, and more preferably at 170-210°C for 5-60 minutes. Any known crosslinking method can be used, such as press crosslinking.

[0099] Secondary crosslinking is preferably carried out at 180-320°C for 2-24 hours, and more preferably at 280-310°C for 5-20 hours. STEP crosslinking is also acceptable. Any known crosslinking method may be used, such as oven crosslinking.

[0100] Although embodiments have been described above, it should be understood that various modifications to the form and details are possible without departing from the spirit and scope of the claims. [Examples]

[0101] The present disclosure will now be explained with reference to examples, but the present disclosure is not limited to such examples.

[0102] Each value in the examples was measured by the following method.

[0103] (1) Color of the solution after the decomposition reaction The transmittance of the solution after the decomposition reaction was measured using an Agilent Cary 7000 UMS, and the average value of %T in the 380-780 nm range was used as the transmittance. A higher transmittance value indicates a lighter color and fewer impurities in the solution.

[0104] (Manufacturing of crosslinked fluororubber compositions) The materials were mixed according to the compositions shown in Table 1 and kneaded in an open roll to obtain fluororubber compositions 1 to 3. Fluororubber composition 1 was pressed at 160°C for 10 minutes, followed by further heat treatment in an oven at 180°C for 4 hours to obtain crosslinked body 1. Fluororubber composition 2 was pressed at 170°C for 15 minutes, followed by further heat treatment in an oven at 230°C for 24 hours to obtain crosslinked body 2. The materials listed in Table 1 are as follows: Fluororubber 1: VdF / HFP = 78 / 22 (mol%), Mooney viscosity (ML) 1+10 (100℃) = 70 Fluororubber 2: VdF / HFP = 78 / 22 (mol%), Mooney viscosity (ML) 1+10 (100℃) = 57 Carbon Black: Product name "Thermax N990", manufactured by Cancarb. Crosslinking agent 1: Perhexa 25B (2,5-dimethyl-2,5-di(t-butylperoxy)hexane, manufactured by NOF Corporation) Crosslinking agent 2: Bisphenol AF Crosslinking agent: TAIC (Triallyl isocyanurate, manufactured by Nippon Chemical Corporation) Crosslinking accelerator: 8-benzyl-1,8-diazabicyclo[5.4.0]-7-undecenium chloride (DBU-B) Acid acceptor 1: Calcium hydroxide (product name "CALDIC#2000", manufactured by Kawamoto Co., Ltd.) Acid absorber 2: Magnesium oxide (product name "Kyowa Mag") TM 150 (Manufactured by Kyowa Chemical Industry Co., Ltd.)

[0105] (Freeze-grinding of the sample) Freeze-grinding was performed using the "JFC-5000" manufactured by Nippon Analytical Industry Co., Ltd. 10 mg of the sample and a 250 mm diameter stainless steel ball were added to a 75 mL sample container. After cooling with liquid nitrogen for 10 minutes, the sample was ground at 50 Hz and a grinding temperature of -196 °C for 10 minutes. This process was repeated twice to obtain a powder sample with a maximum linear length of 200 μm. Fluororubber 1, crosslinked material 1, and 2 were ground using this procedure and used in the following examples and comparative examples.

[0106] (Example 1) 30 mg of crosslinking agent 1 and 10 mL of 0.1 M potassium hydroxide aqueous solution were placed in a hot water reactor, pressurized to 0.5 MPa with argon gas, and reacted at 230°C for 6 hours. The reaction pressure was 3.4 MPa. After the reaction was complete, the contents were cooled to room temperature, and the yield of fluoride ions was confirmed by ion chromatography to quantify the fluoride ions generated in the aqueous phase. The results are shown in Table 2.

[0107] (Example 2) In Example 1, the reaction was carried out in the same manner as in Example 1, except that a 0.2 M potassium hydroxide aqueous solution was used instead of a 0.1 M potassium hydroxide aqueous solution, and the reaction pressure was changed from 3.4 MPa to 3.5 MPa. The results are shown in Table 2. Furthermore, calcium fluoride was obtained by centrifuging the aqueous solution after the reaction to remove the solid components, adding a stoichiometric amount of calcium hydroxide to the aqueous phase, and then washing with hydrochloric acid.

[0108] (Example 3) 30 mg of crosslinking agent 1 and 10 mL of 0.1 M potassium hydroxide aqueous solution were placed in a hot water reactor, pressurized to 0.5 MPa with argon gas, and reacted at 200°C for 18 hours. The reaction pressure was 2.3 MPa. After the reaction was complete, the contents were cooled to room temperature, and the yield of fluoride ions was confirmed by ion chromatography to quantify the fluoride ions generated in the aqueous phase. The results are shown in Table 2.

[0109] (Example 4) In Example 3, the reaction was carried out in the same manner as in Example 1, except that a 0.3 M potassium hydroxide aqueous solution was used instead of a 0.1 M potassium hydroxide aqueous solution, and the reaction time was changed from 18 hours to 6 hours. The results are shown in Table 2.

[0110] (Example 5) 30 mg of fluororubber and 10 mL of 0.1 M potassium hydroxide aqueous solution were placed in a hot water reactor, pressurized to 0.5 MPa with argon gas, and reacted at 230°C for 6 hours. The reaction pressure was 3.4 MPa. After the reaction was complete, the contents were cooled to room temperature, and the yield of fluoride ions was confirmed by ion chromatography to quantify the fluoride ions generated in the aqueous phase. The results are shown in Table 2.

[0111] (Example 6) 30 mg of crosslinking compound 2 and 10 mL of 0.2 M potassium hydroxide aqueous solution were placed in a hot water reactor, pressurized to 0.5 MPa with argon gas, and reacted at 200°C for 18 hours. The reaction pressure was 2.2 MPa. After the reaction was complete, the contents were cooled to room temperature, and the yield of fluoride ions was confirmed by ion chromatography to quantify the fluoride ions generated in the aqueous phase. The results are shown in Table 2.

[0112] (Example 7) 30 mg of fluororubber and 10 mL of 0.2 M sodium hydroxide aqueous solution were placed in a hot water reactor, pressurized to 0.5 MPa with argon gas, and reacted at 200°C for 18 hours. The reaction pressure was 2.3 MPa. After the reaction was complete, the contents were cooled to room temperature, and the yield of fluoride ions was confirmed by ion chromatography to quantify the fluoride ions generated in the aqueous phase. The results are shown in Table 2.

[0113] (Example 8) 30 mg of fluororubber and 10 mL of 0.2 M potassium hydroxide aqueous solution were placed in a hot water reactor, pressurized to 0.5 MPa with argon gas, and reacted at 200°C for 18 hours. The reaction pressure was 2.2 MPa. After the reaction was complete, the contents were cooled to room temperature, and the yield of fluoride ions was confirmed by ion chromatography to quantify the fluoride ions generated in the aqueous phase. The results are shown in Table 2.

[0114] (Comparative Example 1) 30 mg of crosslinking agent 1 and 10 mL of 0.3 M potassium hydroxide aqueous solution were placed in a hot water reactor, pressurized to 0.5 MPa with argon gas, and reacted at 250°C for 6 hours. The reaction pressure was 5.7 MPa. After the reaction was complete, the contents were cooled to room temperature, and the yield of fluoride ions was confirmed by ion chromatography to quantify the fluoride ions generated in the aqueous phase. The results are shown in Table 2.

[0115] (Comparative Example 2) 30 mg of fluororubber and 10 mL of 0.5 M potassium hydroxide aqueous solution were placed in a hot water reactor, pressurized to 0.5 MPa with argon gas, and reacted at 250°C for 6 hours. The reaction pressure was 4.4 MPa. After the reaction was complete, the contents were cooled to room temperature, and the yield of fluoride ions was confirmed by ion chromatography to quantify the fluoride ions generated in the aqueous phase. The results are shown in Table 2.

[0116] (Comparative Example 3) 30 mg of crosslinking agent 1 and 10 mL of 1.0 M potassium hydroxide aqueous solution were placed in a hot water reactor, pressurized to 0.5 MPa with argon gas, and reacted at 250°C for 6 hours. The reaction pressure was 4.2 MPa. After the reaction was complete, the contents were cooled to room temperature, and the yield of fluoride ions was confirmed by ion chromatography to quantify the fluoride ions generated in the aqueous phase. The results are shown in Table 2.

[0117] [Table 1]

[0118] [Table 2]

Claims

1. A method for decomposing a fluorine-containing polymer, comprising a decomposition step of reacting a fluorine-containing polymer having hydrogen atoms in its molecule with subcritical water at a temperature of 180°C or higher and less than 250°C, in which the concentration of at least one basic compound selected from the group consisting of alkali metal hydroxides and alkaline earth metal hydroxides is 0.5 M or less.

2. The method for decomposing a fluorine-containing polymer according to claim 1, wherein the temperature of the subcritical water in the decomposition step is 200°C or higher.

3. The method for decomposing a fluorine-containing polymer according to claim 1 or 2, wherein the fluorine-containing polymer is fluororubber.

4. The method for decomposing a fluorine-containing polymer according to claim 3, wherein the object to be decomposed in the decomposition step is a crosslinked body of the composition containing the fluororubber.

5. A method for decomposing a fluorine-containing polymer according to claim 1 or 2, comprising a grinding step of grinding the fluorine-containing polymer into pulverized particles having a maximum straight length of 3 mm or less, prior to the decomposition step.

6. The method for decomposing a fluorine-containing polymer according to claim 1 or 2, wherein the basic compound is sodium hydroxide and / or potassium hydroxide.

7. A method for decomposing a fluorine-containing polymer according to claim 1 or 2, further comprising a recovery step of adding calcium hydroxide to the aqueous solution after decomposition and recovering the generated calcium fluoride.

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