Silver nanowires and method for producing same, and silver nanowire ink and transparent conductive film
To provide thin and long silver nanowires covered with an organic protective agent containing a less amount of impurities, the silver nanowires having good dispersibility in an ink having an alcohol added thereto. Silver nanowires containing covered thereon a copolymer composition containing one or more kinds of a copolymer having a vinylpyrrolidone structural unit, and having a sulfur content Sppm of 2,000 ppm or less and a residual vinylpyrrolidone monomer content ratio VP R obtained from an NMR spectrum of 6.0% or less, the silver nanowires having an average diameter of 30 nm or less and an average length of 10 μm or more.
1. Silver nanowires comprising covered thereon a copolymer composition containing one or more kinds of a copolymer having a vinylpyrrolidone structural unit, and having a sulfur content Sppm of 2,000 ppm or less and a residual vinylpyrrolidone monomer content ratio VP R defined by the following expression (1) of 6.0% or less, the silver nanowires having an average diameter of 30 nm or less and an average length of 10 μm or more:
VP R (%)=(2×( A+B )/(3× C ))×100 (1)
wherein A represents an integrated value of a peak (7.0 to 7.2 ppm) derived from methine protons of a C═C double bond of the vinylpyrrolidone monomer in an NMR spectrum of the copolymer composition; B represents an integrated value of a peak (4.3 to 4.4 ppm) derived from methylene protons of a C═C double bond of the vinylpyrrolidone monomer in the spectrum; and C represents an integrated value of a peak (3.0 to 3.4 ppm) derived from methylene protons adjacent to a N atom of the copolymer in the spectrum.
2. The silver nanowires according to claim 1 , wherein the copolymer composition has a weight average molecular weight Mw of the copolymer of from 30,000 to 300,000.
3. The silver nanowires according to claim 1 , wherein the copolymer composition has a ratio Sppm/Mw of the sulfur content Sppm (ppm) and a weight average molecular weight Mw of the copolymer of 0.040 or less.
4. The silver nanowires according to claim 1 , wherein one or more kinds of the copolymer constituting the copolymer composition each have a polymerization composition with vinylpyrrolidone and one kind or two or more kinds of a monomer selected from a diallyldimethylammonium salt, ethyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 4-hydroxybutyl acrylate, N-methylmaleimide, N-ethylmaleimide, N-propylmaleimide, and N-tert-butylmaleimide.
5. A silver nanowire ink comprising a liquid medium and therein the silver nanowires according to claim 1 in an amount of from 0.02 to 5.0% by mass in terms of mass ratio of metallic silver.
6. A transparent conductive film comprising the silver nanowires according to claim 1 in a presence density of from 5 to 500 mg/m 2 in terms of mass of metallic silver.
7. The transparent conductive film according to claim 6 , wherein the transparent conductive film has a surface resistance of 200 Ω/sq or less and a haze of 2.0% or less.
8. A method for producing silver nanowires, comprising reduction-depositing silver into a wire form in an alcohol solvent having dissolved therein a silver compound and an organic protective agent, the organic protective agent being a copolymer composition containing one or more kinds of a copolymer having a vinylpyrrolidone structural unit, and having a sulfur content Sppm of 2,000 ppm or less and a residual vinylpyrrolidone monomer content ratio VP R defined by the following expression (1) of 6.0% or less, the silver nanowires having an average diameter of 30 nm or less and an average length of 10 μm or more:
VP R (%)=(2×( A+B )/(3× C ))×100 (1)
wherein A represents an integrated value of a peak (7.0 to 7.2 ppm) derived from methine protons of a C═C double bond of the vinylpyrrolidone monomer in an NMR spectrum of the copolymer composition; B represents an integrated value of a peak (4.3 to 4.4 ppm) derived from methylene protons of a C═C double bond of the vinylpyrrolidone monomer in the spectrum; and C represents an integrated value of a peak (3.0 to 3.4 ppm) derived from methylene protons adjacent to a N atom of the copolymer in the spectrum.
9. The method for producing silver nanowires according to claim 8 , wherein the copolymer composition has a weight average molecular weight Mw of the copolymer of from 30,000 to 300,000.
10. The method for producing silver nanowires according to claim 8 , wherein the copolymer composition has a ratio Sppm/Mw of the sulfur content Sppm (ppm) and a weight average molecular weight Mw of the copolymer of 0.040 or less.
11. The method for producing silver nanowires according to claim 8 , wherein one or more kinds of the copolymer constituting the copolymer composition each have a polymerization composition with vinylpyrrolidone and one kind or two or more kinds of a monomer selected from a diallyldimethylammonium salt, ethyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 4-hydroxybutyl acrylate, N-methylmaleimide, N-ethylmaleimide, N-propylmaleimide, and N-tert-butylmaleimide.