Method of manufacturing transparent conductive film containing carbon nanotubes and binder, and transparent conductive film manufactured thereby
This invention relates to a method of manufacturing a transparent conductive film containing carbon nanotubes and a binder, in which the carbon nanotubes are subjected to acid treatment, dispersion in a solvent, mixing with the binder, and application on the substrate, and to a transparent conductive film manufactured thereby. The method includes subjecting carbon nanotubes having an outer diameter of less than 15 nm to acid treatment to thus purify and surface functionalize them, followed by dispersing the treated carbon nanotubes in a solvent along with the binder, or mixing a carbon nanotube solution using a polar or nonpolar solvent with a binder solution, and applying the mixture on the substrate. Through the application of the mixture of treated carbon nanotubes and binder on the substrate, the transparent conductive film has improved transparency, electrical conductivity, dispersibility, substrate adhesiveness, chemical stability, durability and scratch resistance, and can be applied to various substrates, including hard or flexible substrates, thanks to high substrate adhesiveness and applicability. A solution in which the surface functionalized carbon nanotubes are well dispersed is prepared, thus facilitating the manufacture of the film using various materials and generating economic benefits.
1. A method of manufacturing a transparent conductive film containing carbon nanotubes and a binder, comprising:
1) treating the carbon nanotubes with an acid solution to realize a surface functionalization on the carbon nanotubes by introducing carboxyl group to end portions and surface of the carbon nanotubes, thereby increasing dispersibility of the carbon nanotubes to a solvent, wherein the acid solution is one selected from the group of acids consisting of nitric acid, hydrochloric acid, and sulfuric acid;
2) washing the surface functionalized carbon nanotubes with distilled water to remove the acid solution;
3) filtering the surface functionalized carbon nanotubes;
4) drying the surface functionalized carbon nanotubes;
5) dispersing the surface functionalized carbon nanotubes in the solvent to prepare a carbon nanotube solution, wherein the solvent is either a polar solvent or a nonpolar solvent;
6) mixing a dispersion stabilizer into the carbon nanotube solution to further increase dispersibility of the surface functionalized carbon nanotubes in the solvent;
7) mixing the carbon nanotube solution with the binder, thus preparing a carbon nanotube/binder coating solution;
8) applying the carbon nanotube/binder coating solution on a surface of a substrate; and
9) drying the substrate applied with the carbon nanotube/binder coating solution to remove the solvent and to solidify the binder.
2. The method as set forth in claim 1 , wherein the) step of dispersing the surface functionalized carbon nanotubes in the solvent is conducted through ultrasonic dispersion or ball milling.
3. The method as set forth in claim 2 , wherein the ultrasonic dispersion is conducted for 1˜60 hours using a sonicator having power ranging from 50 W to 700 W at a frequency ranging from 20 kHz to 50 kHz.
4. The method as set forth in claim 1 , wherein the) step of mixing the carbon nanotube solution with the binder is conducted by preparing a binder solution, including the binder and the polar or nonpolar solvent, which is then mixed with the carbon nanotube solution.
5. The method as set forth in claim 1 , further comprising a step for controlling a viscosity of the carbon nanotube/binder coating solution, before the step of applying the carbon nanotube/binder coating solution on the surface of the substrate, wherein the viscosity of the carbon nanotube/binder coating solution is controlled by using an additional solvent suitable for a coating method or through vacuum distillation.
6. The method as set forth in claim 1 , wherein the carbon nanotubes comprise one selected from among single-walled carbon nanotubes, double-walled carbon nanotubes, multi-walled carbon nanotubes, and mixtures thereof.
7. The method as set forth in claim 1 , wherein the solvent comprises one or more selected from among acetone, methylalcohol, ethylalcohol, ethyleneglycol, polyethyleneglycol, tetrahydrofuran, dimethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone, hexane, cyclohexanone, toluene, chloroform, distilled water, dichlorobenzene, dimethylbenzene, trimethylbenzene, pyridine, methylnaphthalene, nitromethane, acrylonitrile, octadecylamine, aniline, and dimethylsulfoxide.
8. The method as set forth in claim 1 , wherein the binder is added in an amount of 15˜50 parts by weight, based on 100 parts by weight of a mixture of carbon nanotubes and binder, in which the binder comprises one or more of organic materials selected from the group consisting of thermoplastic resins, thermosetting resins, light curable resins, silane compounds, polymeric copolymers, self-assembled resins, and combinations thereof.
9. The method as set forth in claim 1 , wherein the substrate comprises one selected from among glass, crystal, glass wafers, silicon wafers, and plastics.
10. The method as set forth in claim 1 , wherein the applying the carbon nanotube/binder coating solution on the surface of the substrate is conducted through any one selected from among spraying, dip coating, spin coating, screen coating, ink-jet printing, pad printing, knife coating, kiss coating, and gravure coating.
11. The method as set forth in claim 1 , wherein the carbon nanotubes are multi-walled carbon nanotubes having an outer diameter of less than 15 nm.
12. The method as set forth in claim 1 , wherein the carbon nanotubes are single-walled carbon nanotubes containing semi-conductive carbon nanotubes and metallic carbon nanotubes.
13. The method as set forth in claim 1 , wherein the solvent is made of a mixture of dimethyllformamide, tetrahydrofuran, ethanol, acetone and dimethylacetamide.
14. The method as set forth in claim 1 , wherein the binder is a light curable acrylate epoxy.
15. The method as set forth in claim 14 , further comprising a step of subjecting the substrate to radiating light at a wavelength of 320 nm and intensity of 30 mW/cm 2 for 1 ˜2 minutes after the step of drying the applied carbon nanotube/binder coating solution.