Method for decomposing fluorine-containing polymer

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] The present disclosure relates to a method for decomposing fluorine-containing polymers.

Background Art

[0002] Due to the high chemical stability and heat resistance of fluorine-containing polymers, not only high temperatures are required for incineration in waste treatment, but also the deterioration of incinerator materials due to the generated hydrogen fluoride is remarkable. Therefore, a new waste treatment method that is neither incineration nor landfill is required. For example, Patent Documents 1 and 2 and Non-Patent Document 1 describe a method of decomposing a fluorine-containing polymer by reacting it in subcritical water containing a basic compound such as potassium hydroxide.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Non-Patent Documents

[0004]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] An object of the present disclosure is to provide a method for decomposing a fluorine-containing polymer that can decompose the fluorine-containing polymer while suppressing the generation of impurities after the decomposition reaction.

Means for Solving the Problems

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

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

[0008] The present disclosure (3) is a method for decomposing a fluorine-containing polymer according to the present disclosure (1) or (2), wherein the fluorine-containing polymer is a fluororubber.

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

[0010] The present disclosure (5) is a method for decomposing a fluorine-containing polymer in any combination with the present disclosure (1) to (4), which includes a pulverization step of pulverizing the fluorine-containing polymer into pulverized particles having a maximum linear length of 3 mm or less before the decomposition step.

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

[0012] The present disclosure (7) is a method for decomposing a fluorine-containing polymer in any combination with the present disclosure (1) to (6), which includes a recovery step of adding calcium hydroxide to the aqueous solution after the decomposition step and recovering the produced calcium fluoride.

Advantages of the Invention

[0013] According to the present disclosure, it is possible to provide a method for decomposing a fluorine-containing polymer that can decompose the fluorine-containing polymer while suppressing the generation of impurities after the decomposition reaction.

Mode for Carrying Out the Invention

[0014] Hereinafter, the present disclosure will be specifically described.

[0015] The present disclosure relates to a method for decomposing a fluorine-containing polymer, which includes a decomposition step of reacting a fluorine-containing polymer in subcritical water at a temperature of 180°C or higher and lower than 250°C and with a concentration of at least one basic compound selected from the group consisting of alkali metal hydroxides and alkaline earth metal hydroxides of 0.5 M or less. Since the method for decomposing a fluorine-containing polymer of the present 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 the present disclosure, a fluorine-containing polymer is treated in subcritical water containing a basic compound. At this time, it is considered that the polymer is decomposed by HF being extracted from the polymer by the basic compound. According to such a mechanism, it is considered that decomposition according to the present disclosure is difficult for polymers without hydrogen atoms, such as polytetrafluoroethylene (PTFE). Therefore, it is preferable that polymers without hydrogen atoms are excluded from the application of the present disclosure.

[0017] Also, in the present disclosure, as described above, it is considered that decomposition occurs by HF being extracted from the polymer. Although fluorine atoms are removed from the polymer, the polymer is not completely decomposed into carbon dioxide. However, since removing fluorine atoms from the polymer is achieved, in the present disclosure, even such a decomposition that is not completely decomposed into carbon dioxide is treated as polymer decomposition.

[0018] Subcritical water is water in a liquid state that exceeds 100°C and is in a temperature range lower than the critical temperature of 374°C by being pressurized. Subcritical water has properties different from those of water at 100°C or lower. Particularly, in the range of 200°C to 300°C, the relative permittivity of subcritical water significantly decreases, showing almost the same fat solubility as methanol or acetone at room temperature, or 10 at room temperature. -14The ionic product was 10 mol / L -11 on the order of mol / L, and the concentrations of hydrogen ions and hydroxide ions became 30 times higher than those of water at room temperature. Therefore, it is known that especially subcritical water at 200°C to 300°C exhibits reactivity different from that of water at room temperature. In the decomposition method of the present disclosure, the temperature of the subcritical water in the above decomposition step is less than 250°C, preferably 245°C or less, more preferably 240°C or less, still more preferably 235°C or less, and also 180°C or more, preferably 200°C or more, more preferably 205°C or more, still more preferably 210°C or more, still more preferably 215°C or more, particularly preferably 220°C or more, and extremely preferably 225°C or more.

[0019] The water used for preparing subcritical water is not particularly limited, and any water such as tap water, ion-exchanged water, distilled water, well water, etc. may be used. However, from the viewpoint of suppressing side reactions due to the influence of coexisting salts, etc., ion-exchanged water and distilled water are preferably mentioned. Regarding the amount of water used, it is sufficient if the fluorine-containing polymer to be treated is sufficiently immersed. However, care is required because if the amount of water introduced into the closed container for pressurization is extremely small, all of it will become water vapor after heating and will not be in the state of subcritical water.

[0020] In the decomposition method of the present disclosure, at least one basic compound selected from the group consisting of alkali metal hydroxides and alkaline earth metal hydroxides is used. As already described, the basic compound is used to cause a reaction to extract HF from the fluorine-containing polymer.

[0021] Examples of the alkali metal hydroxide include lithium hydroxide, sodium hydroxide, potassium hydroxide, cesium hydroxide, etc. Among these, sodium hydroxide and / or potassium hydroxide is preferable. Here, potassium hydroxide is known to have a higher activity and higher basicity than sodium hydroxide in a concentrated solution, and high activity is expected in the extraction reaction of HF. Actually, in the present disclosure, it has been confirmed that when decomposing a fluorine-containing polymer using potassium hydroxide, the activity is higher than when using sodium hydroxide. From such a viewpoint, it can be said that potassium hydroxide is most preferable.

[0022] Examples of the alkaline earth metal hydroxide include calcium hydroxide, barium hydroxide, etc.

[0023] The concentration of the basic compound in the subcritical water is 0.5 M or less, preferably 0.45 M or less, more preferably 0.40 M or less, still more preferably 0.35 M or less, and preferably 0.01 M or more, more preferably 0.05 M or more, still more preferably 0.10 M or more, and still 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 is preferably 12 or more, more preferably 12.7 or more, still more preferably 13 or more, and preferably 13.7 or less, more preferably 13.6 or less, still more preferably 13.5 or less.

[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 a fluorine-containing polymer to be treated are added to a pressure vessel sized according to the amount of the 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 may be enclosed. Examples of such a gas include air, argon, nitrogen, etc. The degree of pressurization can be about 0.5 MPa, but is not particularly limited.

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

[0027] In the aqueous solution after the decomposition reaction, the fluorine atoms contained in the fluorine-containing polymer are contained as fluoride ions. The decomposition method of the present disclosure preferably includes a recovery step of adding calcium hydroxide to the aqueous solution after the decomposition step and recovering the produced calcium fluoride. The fluoride ions contained in the aqueous solution after the decomposition react with calcium ions generated from the added calcium hydroxide, and can be converted into calcium fluoride, which is a raw material for all fluorine compounds. By including the above recovery step, the decomposition method of the present disclosure enables effective utilization of resources. Further, as described above, the decomposition method of the fluorine-containing polymer of the present disclosure can suppress the generation of impurities after the decomposition reaction, so that the impurities during the recovery of calcium fluoride can also be reduced.

[0028] In addition, the aqueous solution after the decomposition reaction contains, in addition to fluoride ions, the polymer decomposition product after HF has been extracted. As already described, this decomposition product is considered to be elemental carbon having a double bond and often exhibits a black color. Since this is a solid, it can be easily separated, and since the fluorine atoms have been removed by the above recovery step, it is also easy to incinerate.

[0029] The decomposition method of the present disclosure preferably includes a pulverization step of pulverizing the fluorine-containing polymer into pulverized particles having a maximum linear length of 3 mm or less before the above decomposition step. By including the above pulverization step in the decomposition method of the present disclosure, the fluorine-containing polymer becomes easier to decompose.

[0030] The pulverization method is not particularly limited, and examples thereof include cryogenic pulverization, disk mill, hammer mill, mortar type pulverizer, jet mill, and the like.

[0031] The pulverization temperature is preferably -200°C or higher and preferably 90°C or lower. More preferably, it is 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 particularly preferably 500 μm or less. Also, 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 diameter 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 above maximum linear length was observed by using SEM images for 100 or more secondary particles, and the major axis of each secondary particle was measured. The largest major axis among them was taken as the maximum linear length.

[0034] The transmittance of the aqueous solution after the decomposition reaction can be measured using Agilent Cary 7000 UMS. At this time, the average value of %T in the range of 380 to 780 nm was taken as the transmittance. The larger the numerical value of the transmittance, the lighter the color of the solution and the fewer the impurities.

[0035] The transmittance of the aqueous solution after the decomposition reaction is preferably 40%T or more, more preferably 50%T or more, and even more preferably 70%T or more. The upper limit is not particularly limited and may be 100%T, but is usually about 90%T. When the transmittance of the aqueous solution after the decomposition reaction is within the above range, after the decomposition step, calcium hydroxide can be added to the aqueous solution after decomposition to reduce the amount of impurities contained in the generated calcium fluoride.

[0036] The fluorine-containing polymer to be decomposed in the present disclosure is a polymer containing fluorine atoms in the molecule, and any polymer containing even one fluorine atom in the molecule is a decomposition target of the present disclosure. Fluorine-containing polymers are evaluated for their properties such as high chemical resistance, heat resistance, and weather resistance, and are applied in various fields including industry and medicine. On the other hand, these polymers are not easily decomposed as a reverse side of such high chemical stability and heat durability. The present disclosure provides a method for chemically decomposing these polymers. Such fluorine-containing polymers preferably have hydrogen atoms in the molecule. Further, the fluorine-containing polymer may be a fluororesin or a fluororubber, and may be a homopolymer or a copolymer.

[0037] Examples of the fluororesin 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 / perfluoroalkyl allyl ether copolymer, etc. The perfluoroalkyl allyl ether is a monomer represented by CF2=CFCF2-O-Rf 4 (Rf 4 is a perfluoroalkyl group having 1 to 5 carbon atoms).

[0038] Examples of the fluororesin include partially fluorinated polymers and perfluoropolymers, and a partially fluorinated polymer is preferred.

[0039] Among them, 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, and VdF / HFP copolymer and VdF / TFE / HFP copolymer are more preferred.

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

[0041] Examples of the above fluororubber include partially fluorinated rubber and perfluororubber, with partially fluorinated rubber being preferred.

[0042] Examples of the above partially fluorinated rubber 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, ethylene / hexafluoropropylene (HFP) / tetrafluoroethylene (TFE)-based fluororubber, etc. Among them, it is preferably at least one 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 composed of 45 to 85 mol% of vinylidene fluoride and 55 to 15 mol% of at least one other monomer copolymerizable with vinylidene fluoride. Preferably, it is a copolymer composed of 50 to 80 mol% of vinylidene fluoride and 50 to 20 mol% of at least one other monomer copolymerizable with vinylidene fluoride.

[0044] In this specification, the content of each monomer constituting the fluoropolymer can be calculated by appropriately combining NMR, FT-IR, elemental analysis, and fluorescent X-ray analysis according to the type of monomer.

[0045] As at least one other monomer copolymerizable with the above vinylidene fluoride, tetrafluoroethylene [TFE], hexafluoropropylene [HFP], fluoroalkyl vinyl ether, trifluoroethylene, trifluoropropylene, pentafluoropropylene, trifluorobutene, tetrafluoroisobutene, hexafluoroisobutene, vinyl fluoride, perfluoroalkyl allyl ether, 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).) fluoromonomers, monomers such as monomers providing crosslinking sites; non-fluorinated monomers such as ethylene, propylene, and alkyl vinyl ether can be mentioned. These can be used alone or in any 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 containing 1 to 3 oxygen atoms) a fluoromonomer represented by, and, General formula (10): CF2 = CFO(CF2CF(Y 10 )O) m (CF2) n F (wherein, Y 10 represents a fluorine atom or a trifluoromethyl group. m is an integer of 1 to 4. n is an integer of 1 to 4.). It is preferably at least one selected from the group consisting of fluoromonomers represented by the general formula (8), and more preferably a fluoromonomer represented by the general formula (8). As the perfluoroalkyl allyl ether, General formula (11): CF2 = CF - CF2ORf 111 (wherein, Rf 111 represents a perfluoroalkyl group having 1 to 5 carbon atoms.). A fluoromonomer represented by the formula is preferred.

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

[0047] The above - mentioned VdF / CH2 = CFCF3 - based rubber is preferably a copolymer composed of 40 to 99.5 mol% of VdF and 0.5 to 60 mol% of CH2 = CFCF3, and more preferably a copolymer composed of 50 to 85 mol% of VdF and 20 to 50 mol% of CH2 = CFCF3.

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

[0049] The monomer that provides a crosslinking site is a monomer having a crosslinkable group that provides a crosslinking site for forming a crosslink by a crosslinking agent in the fluoropolymer (cure site monomer).

[0050] Examples of the monomer that provides a crosslinking site include 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 is an iodine atom or a bromine atom) a fluoromonomer represented by 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 is a fluoroalkylene group, a perfluoroalkylene group, a fluoropolyoxyalkylene group or a perfluoropolyoxyalkylene group, X 4 is an iodine atom or a bromine atom) a fluoromonomer represented by 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 is a fluoromonomer represented by a cyano group, a carboxyl group, an alkoxycarbonyl group, an iodine atom, a bromine atom, or -CH2I, and 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, and X 6 is a cyano group, a carboxyl group, an alkoxycarbonyl group, an iodine atom, a bromine atom, or -CH2OH), and a fluoromonomer represented by the formula, 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 and are a hydrogen atom or an alkyl group having 1 to 5 carbon atoms. Z is a linear or branched alkylene group having 1 to 18 carbon atoms, which may have an oxygen atom, a cycloalkylene group having 3 to 18 carbon atoms, an alkylene group or oxyalkylene group having 1 to 10 carbon atoms that is at least partially fluorinated, or -(Q) p -CF2O-(CF2CF2O) m (CF2O) n -CF2-(Q) p - (In the formula, Q is an alkylene group or an oxyalkylene group. p is 0 or 1. m / n is 0.2 to 5.) is preferably at least one selected from the group consisting of monomers represented by a (per)fluoropolyoxyalkylene group having a molecular weight of 500 to 10,000.)

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

[0052] As the monomer that provides the crosslinking site, at least one selected from the group consisting of 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(CF3)CF2OCF(CF3)CH2OH, CH2=CHCF2CF2I, CH2=CH(CF2)2CH=CH2, CH2=CH(CF2)6CH=CH2, and CF2=CFO(CF2)5CN is preferable, and at least one selected from the group consisting of CF2=CFOCF2CF(CF3)OCF2CF2CN and CF2=CFOCF2CF2CH2I is more preferable.

[0053] From the viewpoint of excellent compression set characteristics at high temperatures, the fluororubber preferably has a glass transition temperature of -70°C or higher, more preferably -60°C or higher, and still more preferably -50°C or higher. Also, from the viewpoint of good cold resistance, it is preferably 5°C or lower, more preferably 0°C or lower, and still more preferably -3°C or lower.

[0054] The glass transition temperature can be determined as the temperature indicating the midpoint of two intersections between the extension line of the baseline before and after the secondary transition of the DSC curve and the tangent line at the inflection point of the DSC curve, by using a differential scanning calorimeter (DSC822e manufactured by Mettler Toledo), obtaining a DSC curve by heating 10 mg of the sample at a rate of 10 °C / min.

[0055] The above fluororubber preferably has a Mooney viscosity ML at 170 °C of 30 or more, more preferably 40 or more, and still more preferably 50 or more, in terms of good heat resistance. Also, in terms of good processability, it is preferably 150 or less, more preferably 120 or less, and still more preferably 110 or less. (1+20) The above fluororubber preferably has a Mooney viscosity ML at 170 °C of 30 or more, more preferably 40 or more, and still more preferably 50 or more, in terms of good heat resistance. Also, in terms of good processability, it is preferably 150 or less, more preferably 120 or less, and still more preferably 110 or less.

[0056] The above fluororubber preferably has a Mooney viscosity ML at 140 °C of 30 or more, more preferably 40 or more, and still more preferably 50 or more, in terms of good heat resistance. Also, in terms of good processability, it is preferably 180 or less, more preferably 150 or less, and still more preferably 110 or less. (1+20) The above fluororubber preferably has a Mooney viscosity ML at 140 °C of 30 or more, more preferably 40 or more, and still more preferably 50 or more, in terms of good heat resistance. Also, in terms of good processability, it is preferably 180 or less, more preferably 150 or less, and still more preferably 110 or less.

[0057] The above fluororubber preferably has a Mooney viscosity ML at 100 °C of 10 or more, more preferably 20 or more, and still more preferably 30 or more, in terms of good heat resistance. Also, in terms of good processability, it is preferably 120 or less, more preferably 100 or less, and still more preferably 80 or less. (1+10) The above fluororubber preferably has a Mooney viscosity ML at 100 °C of 10 or more, more preferably 20 or more, and still more preferably 30 or more, in terms of good heat resistance. Also, in terms of good processability, it is preferably 120 or less, more preferably 100 or less, and still more preferably 80 or less.

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

[0059] In the decomposition method of the present disclosure, the object to be decomposed in the above decomposition step may be a crosslinked product of a composition containing the above fluororubber. The above composition preferably contains the above fluororubber and a crosslinking agent.

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

[0061] The crosslinking agent used in peroxide crosslinking may be an organic peroxide that can easily generate peroxy radicals in the presence of heat or a redox system. Specifically, for example, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane can be used. Generally, the type and amount of the organic peroxide are selected in consideration of the amount of active -O-O- and the decomposition temperature.

[0062] In addition, as the crosslinking aid that can be used in this case, any compound having reactivity with peroxy radicals and polymer radicals may be used. For example, 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), -CH=CF(CF3), etc. can be mentioned (in each formula, "C6H5" represents a phenyl group). Specifically, for example, triallyl cyanurate, triallyl isocyanurate (TAIC), triacryl formal, triallyl trimellitate, N,N'-n-phenylene bismaleimide, dipropynyl terephthalate, diallyl phthalate, tetraallyl terephthalamide, 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-diallyl acrylamide, 1,6-divinyldodecafluorhexane, etc. can be mentioned.

[0063] In addition, as the crosslinking aid used together with the peroxide crosslinking agent, the general formula (48):

Chemical formula

[0064] As the compound represented by the general formula (48), the general formula (49): [Chemical formula] (In the formula, j is an integer from 2 to 10, preferably an integer from 4 to 8, and the four Rs 32 are each independently H, F, or an alkyl group or (per)fluoroalkyl group having 1 to 5 carbon atoms), a compound represented by the general formula (50): [Chemical formula] (In the formula, Y 31 are each independently F, Cl, or H, and Y 32 are each independently F, Cl, H, or OR 33 (wherein R 33 is a branched or linear alkyl group that may be partially, substantially, or completely fluorinated or chlorinated), and Z 33 is a divalent group having 2 to 10 carbon atoms that may have an ether bond inserted and is optionally fluorinated, preferably Z 33 is a -(CF2) m - group where m is an integer from 3 to 5, and the compound represented by the general formula (50) is preferably F2C=CF-O-(CF2)5-O-CF=CF2), a compound represented by the general formula (51): [Chemical formula] (In the formula, Y 31 , Y 32 and Z 33 are as described above, and R 34 are each independently H, F, or an alkyl group or (per)fluoroalkyl group having 1 to 5 carbon atoms), and examples of the compound represented thereby include etc.

[0065] As the above crosslinking agent or crosslinking aid used together with a peroxide crosslinking agent, the general formula (52): [Chemical formula] (In the formula, R 35 to R 37is, independently of each other, a hydrogen atom, a fluorine atom, an alkyl group, a fluorinated alkyl group, or a substituted or unsubstituted aryl group, and R 35 ~R 37 at least one of which is a fluorine atom or a group containing a fluorine atom. m is an integer from 1 to 5. When m is 2 or more, the m R 35 ~R 37 may be the same or different from each other. The hydrogen atoms of the benzene ring may be substituted. A compound having at least one structure represented by ) can also be mentioned. When m is 1, it is preferable to have two or more of the structures.

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

Chemical formula

[0067] (In the formula, R 35 ~R 37 are as described above. p is an integer from 0 to 2, and n is an integer from 2 to 6.) A compound represented by the 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 the crosslinking agent used for polyol crosslinking include polyhydric alcohol compounds such as bisphenol A and bisphenol AF.

[0070] Examples of the crosslinking agent used for polyamine crosslinking include polyvalent amine compounds such as hexamethylenediamine carbamate, N,N'-dicyclohexylidene-1,6-hexanediamine, and 4,4'-bis(aminocyclohexyl)methane carbamate.

[0071] Examples of the crosslinking agent used for oxazole crosslinking, imidazole crosslinking, and thiazole crosslinking include, for example, the general formula (55):

[0072]

Chemical formula

[0073]

Chemical formula

[0074] is a group represented by, R 42 and R 43 are such that one is -NH2 and the other is -NHR 44 , -NH2, -OH, or -SH, and R 44 is a hydrogen atom, a fluorine atom, or a monovalent organic group, and preferably R 42 is -NH2 and R 43 is -NHR 44 .). Examples thereof include bisdiaminophenyl-based crosslinking agents, bisaminophenol-based crosslinking agents, and bisaminothiophenol-based crosslinking agents.

[0075] Preferable specific examples of the alkylene group having 1 to 6 carbon atoms include a methylene group, an ethylene group, a propylene group, a butylene group, a pentylene group, a hexylene group, etc., and examples of the perfluoroalkylene group having 1 to 10 carbon atoms include [Chemical formula] Examples include etc.

[0076] These compounds are known as examples of bis(diaminophenyl) compounds in, for example, Japanese Patent Publication No. 2-59177 and Japanese Unexamined Patent Application Publication No. 8-120146.

[0077] As crosslinking agents used for oxazole crosslinking, imidazole crosslinking, and thiazole crosslinking, furthermore, the general formula (56): [Chemical formula] (In the formula, R 41 is as described above, R 45 is each independently any of the following groups. [Chemical formula] ) A bisamidrazone-based crosslinking agent represented by the general formula (57): [Chemical formula] (In the formula, Rf 41 is a perfluoroalkylene group having 1 to 10 carbon atoms) An amidrazone-based crosslinking agent represented by the general formula (58): [Chemical formula] (In the formula, n is an integer of 1 to 10) A bisamidooxime-based crosslinking agent represented by the general formula (59): HN=CR 45 R 46 (In the formula, R 45 is selected from the group consisting of H, NH2, and NHR 47 , R 46 is selected from the group consisting of Ph, SO2H, NR 48 R 49 , 2-pyridine, and CH2CONH2, R 47 is selected from the group consisting of Ph, NH2, and CN, R 48is selected from the group consisting of H, NHPh, CH2CONH2, a linear alkyl group having 1 to 8 carbon atoms, and a branched alkyl group having 1 to 8 carbon atoms, and R 49 is Ph, COOC(CH3)3, NH2, CH2COOH, CSNH2, CNHNH3 + Cl - , p-phenyl CN,

Chemical formula

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

[0079] Also, as the above crosslinking agent, the general formula (60): X 41 -(CH2) n -R 50 -(CH2) m -X 41 (In the formula, X 41 are each independently an alkyne group, a nitrile group or Y 41 P N3 (Y 41 is SO, SO2, C6H4 or CO, and p is 0 or 1), n and m are independently integers from 1 to 4, and R 50 is i) a fluoroalkylene group having 3 to 10 carbon atoms, ii) a fluoroalkoxylene group having 3 to 10 carbon atoms, iii) a substituted arylene group, iv) an oligomer containing copolymerized units of vinylidene fluoride and perfluoro(methyl vinyl ether), v) an oligomer containing copolymerized units of vinylidene fluoride and hexafluoropropylene, (vi) oligomers containing copolymerized units of tetrafluoroethylene and perfluoro(methyl vinyl ether), and (vii) crosslinking agents selected from the group consisting of oligomers containing copolymerized units of tetrafluoroethylene and hydrocarbon olefins) can also be mentioned. This crosslinking agent is preferably used together with a 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, giving a crosslinked product.

[0080] Particularly preferred examples of the above crosslinking agents include compounds having a plurality of 3-amino-4-hydroxyphenyl groups or 3-amino-4-mercaptophenyl groups, or the general formula (61):

[0081] [Chemical formula]

[0082] (wherein R 41 , R 42 and R 43Examples of the compound represented as described above include, specifically, for example, 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (common name: bis(aminophenol) AF), 2,2-bis(3-amino-4-mercaptophenyl)hexafluoropropane, tetraaminobenzene, bis-3,4-diaminophenylmethane, bis-3,4-diaminophenylether, 2,2-bis(3,4-diaminophenyl)hexafluoropropane, 2,2-bis[3-amino-4-(N-phenylamino)phenyl]hexafluoropropane, 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, 2,2-bis[3-amino-4-(N-benzylamino)phenyl]hexafluoropropane, and the like.

[0083] Among these, as the above crosslinking agent, 2,2-bis[3-amino-4-(N-phenylamino)phenyl]hexafluoropropane is preferable from the viewpoints of heat resistance, steam resistance, amine resistance, and good crosslinking properties.

[0084] The content of the above crosslinking agent is preferably 0.01 to 10 parts by mass, more preferably 0.05 to 5 parts by mass, based on 100 parts by mass of the fluororubber.

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

[0086] Examples of the above 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, polyetherketone, and polyoxybenzoate; 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] In addition, the above inorganic fillers and organic fillers may be blended alone or in combination of two or more.

[0089] The blending amount of the above general filler is preferably 0.5 to 100 parts by mass, more preferably 5 to 50 parts by mass, based on 100 parts by mass of the fluororubber.

[0090] Particularly in fields where high purity and non-contamination are not required, ordinary additives such as fillers, processing aids, plasticizers, colorants, etc. that are blended into the fluoropolymer composition as needed can be blended, and one or more common crosslinking agents and crosslinking aids different from the above may be blended.

[0091] The above composition can be produced by kneading the above fluororubber, the above crosslinking agent, and, if necessary, the above crosslinking accelerator and filler.

[0092] The above kneading can be carried out using ordinary polymer processing machines such as open rolls, Banbury mixers, kneaders, and closed mixers.

[0093] The above crosslinked product can also be produced by molding the above composition and crosslinking the obtained molded product, or by performing molding and crosslinking simultaneously.

[0094] The molding method is not particularly limited, and examples thereof include compression molding, extrusion molding, transfer molding, injection molding, and the like.

[0095] The crosslinking conditions are preferably determined according to the type of crosslinking agent used, etc. For example, it is preferable to crosslink at a temperature of 140 to 300 °C for 1 minute to 24 hours. Also, crosslinking can be carried out under normal pressure, increased pressure, reduced pressure, or in air.

[0096] The crosslinking method is not particularly limited, and steam crosslinking, pressure molding method, or a normal method in which the crosslinking reaction is initiated by heating can be adopted, and a radiation crosslinking method at normal temperature and pressure may also be used.

[0097] Only the first crosslinking treatment (referred to as primary crosslinking) may be sufficient, but a post-treatment called secondary crosslinking may be performed after the primary crosslinking.

[0098] When performing primary crosslinking and secondary crosslinking, the primary crosslinking is preferably carried out at 150 to 250 °C for 5 to 120 minutes, and more preferably at 170 to 210 °C for 5 to 60 minutes. As the crosslinking means, known crosslinking means can be used, and examples thereof include press crosslinking.

[0099] The secondary crosslinking is preferably carried out at 180 to 320 °C for 2 to 24 hours, and more preferably at 280 to 310 °C for 5 to 20 hours. STEP crosslinking may also be used. As the crosslinking means, known crosslinking means can be used, and examples thereof include oven crosslinking.

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

Examples

[0101] Next, the present disclosure will be described with reference to examples, but the present disclosure is not limited to such examples only.

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

[0103] (1) Color of the solution after decomposition reaction The solution after the decomposition reaction was measured for transmittance using Agilent Cary 7000 UMS, and the average value of %T in the range of 380 to 780 nm was taken as the transmittance. The larger the numerical value of the transmittance, the lighter the color of the solution and the fewer the impurities.

[0104] (Manufacture of crosslinked product of fluororubber composition) Each material was mixed with the composition shown in Table 1 and kneaded on an open roll to obtain fluororubber compositions 1 to 3. For the obtained fluororubber composition 1, after pressing at 160 °C for 10 minutes, it was further heat-treated in an oven at 180 °C for 4 hours to obtain crosslinked product 1. For fluororubber composition 2, after pressing at 170 °C for 15 minutes, it was further heat-treated in an oven at 230 °C for 24 hours to obtain crosslinked product 2. Note that the materials shown in Table 1 are as follows. Fluororubber 1: VdF / HFP = 78 / 22 (mol%), Mooney viscosity (ML 1+10 (100 °C)) = 70 Fluororubber 2: VdF / HFP = 78 / 22 (mol%), Mooney viscosity (ML 1+10 (100 °C)) = 57 Carbon black: Trade 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 aid: TAIC (triallyl isocyanurate, manufactured by Taiyo Nippon Sanso Corporation) Crosslinking accelerator: 8-benzyl-1,8-diazabicyclo[5.4.0]-7-undecenium chloride (DBU-B) Acid acceptor 1: Calcium hydroxide (trade name "CALDIC#2000", manufactured by Kawashige Co., Ltd.) Acid acceptor 2: Magnesium oxide (trade name "Kyowa Mag TM 150", manufactured by Kyowa Chemical Industry Co., Ltd.)

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

[0106] (Example 1) 30 mg of cross - linked body 1 and 10 mL of 0.1 M potassium hydroxide aqueous solution were put into a hot - water reactor. After pressurizing to 0.5 MPa with argon gas, the reaction was carried out at 230 °C for 6 hours. The pressure during the reaction was 3.4 MPa. After the reaction, the content was cooled to room temperature, and the fluoride ions generated in the aqueous phase were quantified by ion chromatography to confirm the yield of fluoride ions. 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 0.2 M potassium hydroxide aqueous solution was used instead of 0.1 M potassium hydroxide aqueous solution, and the pressure during the reaction was changed from 3.4 MPa to 3.5 MPa. The results are shown in Table 2. Furthermore, for the aqueous phase obtained by centrifuging the aqueous solution after the reaction to remove the solid content, stoichiometric amount of calcium hydroxide was added, and then calcium fluoride was obtained by washing with hydrochloric acid.

[0108] (Example 3) 130 mg of the crosslinked product 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 then reacted at 200 °C for 18 hours. The pressure during the reaction was 2.3 MPa. After the reaction was completed, the content was cooled to room temperature, and the fluoride ions generated in the aqueous phase were quantified by ion chromatography to confirm the yield of fluoride ions. 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 0.3 M potassium hydroxide aqueous solution was used instead of 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 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 then reacted at 230 °C for 6 hours. The pressure during the reaction was 3.4 MPa. After the reaction was completed, the content was cooled to room temperature, and the fluoride ions generated in the aqueous phase were quantified by ion chromatography to confirm the yield of fluoride ions. The results are shown in Table 2.

[0111] (Example 6) 30 mg of the crosslinked product 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 then reacted at 200 °C for 18 hours. The pressure during the reaction was 2.2 MPa. After the reaction was completed, the content was cooled to room temperature, and the fluoride ions generated in the aqueous phase were quantified by ion chromatography to confirm the yield of fluoride ions. The results are shown in Table 2.

[0112] (Example 7) 30 mg of fluororubber 1 and 10 mL of 0.2 M aqueous sodium hydroxide solution were placed in a hot water reactor, pressurized to 0.5 MPa with argon gas, and then reacted at 200 °C for 18 hours. The pressure during the reaction was 2.3 MPa. After the reaction was completed, the contents were cooled to room temperature, and the fluoride ions generated in the aqueous phase were quantified by ion chromatography to confirm the yield of fluoride ions. The results are shown in Table 2.

[0113] (Example 8) 30 mg of fluororubber 1 and 10 mL of 0.2 M aqueous potassium hydroxide solution were placed in a hot water reactor, pressurized to 0.5 MPa with argon gas, and then reacted at 200 °C for 18 hours. The pressure during the reaction was 2.2 MPa. After the reaction was completed, the contents were cooled to room temperature, and the fluoride ions generated in the aqueous phase were quantified by ion chromatography to confirm the yield of fluoride ions. The results are shown in Table 2.

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

[0115] (Comparative Example 2) 30 mg of fluororubber 1 and 10 mL of 0.5 M aqueous potassium hydroxide solution were placed in a hot water reactor, pressurized to 0.5 MPa with argon gas, and then reacted at 250 °C for 6 hours. The pressure during the reaction was 4.4 MPa. After the reaction was completed, the contents were cooled to room temperature, and the fluoride ions generated in the aqueous phase were quantified by ion chromatography to confirm the yield of fluoride ions. The results are shown in Table 2.

[0116] (Comparative Example 3) 130 mg of the crosslinked product 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 then reacted at 250 °C for 6 hours. The pressure during the reaction was 4.2 MPa. After the reaction, the content was cooled to room temperature, and the fluoride ions generated in the aqueous phase were quantified by ion chromatography to confirm the yield of fluoride ions. 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 the fluorine-containing polymer in subcritical water at a temperature of 180°C or higher and lower than 250°C and with a concentration of at least one basic compound selected from the group consisting of alkali metal hydroxides and alkaline earth metal hydroxides of 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 a 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 product of a composition containing the fluororubber.

5. The method for decomposing a fluorine-containing polymer according to Claim 1 or 2, further comprising a pulverization step of pulverizing the fluorine-containing polymer into pulverized particles having a maximum linear length of 3 mm or less before 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. The 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 the decomposition step and recovering the produced calcium fluoride.

Images