Vinylidene fluoride copolymer composition and method for producing same, polymer dispersion solution, electrode for nonaqueous electrolyte secondary battery, electrolyte layer for nonaqueous electrolyte secondary battery, and nonaqueous electrolyte secondary battery
A vinylidene fluoride copolymer composition having stable dispersibility in a dispersion medium over a long period of time, the composition having a melting temperature of 140° C. or lower, a reversing heat flow of the composition has endothermic peaks having an amount of enthalpy of fusion of 2 J/g or more, and an absolute value of a difference between a temperature showing a largest endothermic peak among the endothermic peaks and the melting temperature of the composition is 10° C. or lower. When a dispersion containing butyl butyrate and the vinylidene fluoride copolymer composition (vinylidene fluoride content rate of 10 mass %) is left to stand for 20 hours, a content rate of the vinylidene fluoride copolymer composition in an upper 20 vol % of the dispersion after the dispersion is left to stand is 4.0 mass % or more and 10 mass % or less.
1 . A method for producing a vinylidene fluoride copolymer composition, the vinylidene fluoride copolymer composition comprising a vinylidene fluoride copolymer containing a structural unit derived from vinylidene fluoride and a structural unit derived from a fluorinated alkyl vinyl compound, the method comprising:
preparing an emulsion containing an untreated vinylidene fluoride copolymer dispersed in an aqueous medium; and
obtaining a surfactant-containing emulsion having a surface tension of 40 mN/m or less at 25° C. by adding an ionic surfactant and stirring into the emulsion,
wherein the vinylidene fluoride copolymer composition has a melting point of 140° C. or lower.
2 . A method for producing a vinylidene fluoride copolymer composition, the vinylidene fluoride copolymer composition comprising a vinylidene fluoride copolymer containing a structural unit derived from vinylidene fluoride and a structural unit derived from a fluorinated alkyl vinyl compound, the method comprising:
preparing an emulsion containing an untreated vinylidene fluoride copolymer dispersed in an aqueous medium by an emulsion polymerization method; and
when measuring a heat flow of the untreated vinylidene fluoride copolymer with a differential scanning calorimeter, heating the emulsion at a temperature which is lower than an endset of a highest-temperature peak among endothermic peaks observed at 185° C. or lower and is 40° C. or higher;
wherein the method further comprises, after the preparing the emulsion and before the heating the emulsion, adding a surfactant to the emulsion; and
wherein the vinylidene fluoride copolymer composition has a melting point of 140° C. or lower.
3 . The method for producing a vinylidene fluoride copolymer composition according to claim 1 , wherein the fluorinated alkyl vinyl compound is hexafluoropropylene.
4 . The method for producing a vinylidene fluoride copolymer composition according to claim 2 , wherein the fluorinated alkyl vinyl compound is hexafluoropropylene.
5 . The method for producing a vinylidene fluoride copolymer composition according to claim 3 , wherein the vinylidene fluoride copolymer composition comprises 15 mass % or more and 70 mass % or less of a structural unit derived from the hexafluoropropylene per 100 mass % of structural units of the vinylidene fluoride copolymer.
6 . The method for producing a vinylidene fluoride copolymer composition according to claim 4 , wherein the vinylidene fluoride copolymer composition comprises 15 mass % or more and 70 mass % or less of a structural unit derived from the hexafluoropropylene per 100 mass % of structural units of the vinylidene fluoride copolymer.
7 . The method for producing a vinylidene fluoride copolymer composition according to claim 1 , wherein the ionic surfactant comprises an anionic surfactant.
8 . The method for producing a vinylidene fluoride copolymer composition according to claim 3 , wherein the ionic surfactant comprises an anionic surfactant.
9 . The method for producing a vinylidene fluoride copolymer composition according to claim 5 , wherein the ionic surfactant comprises an anionic surfactant.