Patterned transparent conductive film and process for producing such a patterned transparent conductive film

Abstract

The invention relates to a patterned transparent conductive film, comprising areas with higher conductivity and areas with lower conductivity, wherein in the areas with higher conductivity nanoobjects are disposed in a binder matrix such that the nanoobjects are interconnected and thereby form an area with higher conductivity and wherein in the areas with lower conductivity the nanoobjects are structurally intact and are coated with an insulating coating material. The invention further relates to a process for producing such a patterned transparent conductive film comprising areas with lower conductivity and areas with higher conductivity, comprising following steps: (a) applying an ink comprising electrically conductive nanoobjects and a binder on a substrate, forming a first layer, wherein the amount of conductive nanoobjects is such that the first layer is conductive after drying; (b) drying of the first layer; (c) applying a mixture comprising an insulating coating material or a precursor of an insulating coating material on that parts of the first layer which shall form the areas with lower conductivity, wherein the insulating coating material or the precursors form an insulating coating around the electrically conductive nanowires; (d) drying of the coated substrate.

Claims

1. A transparent conductive film comprising a pattern of areas having higher conductivity and areas having lower conductivity, relative to one another, wherein: the conductive film comprises a binder matrix and nanoobjects disposed in the binder matrix; the areas with higher conductivity do not comprise an insulating coating material, and the nanoobjects are interconnected and electrically conductive; the areas with lower conductivity comprise an insulating coating material which forms around and encloses the interconnected nanoobjects and reduces electron transfer between said nanoobjects, wherein the as-coated nanoobjects are unbroken; and the nanoobjects have the same identity and the same three external nanoscale dimensions in the areas of higher and lower conductivity, and the nanoobjects are present in the film in substantially the same number density in each of the areas of higher and lower conductivity.

2. The transparent conductive film according to claim 1, wherein the insulating coating material is selected from the group consisting of an insulating oxide, a complex insulating oxide and an insulating polymer.

3. The transparent conductive film according to claim 2, wherein the insulating coating material comprises an insulating oxide selected from the group consisting of SiO.sub.2, Al.sub.2O.sub.3, ZrO.sub.2 graphene oxide and zirconium silicate.

4. The transparent conductive film according to claim 2, wherein the insulating coating material comprises an insulating polymer selected from the group consisting of polystyrene, polyethylene and fluorinated polyimide.

5. The transparent conductive film according to claim 1, wherein the nanoobjects are nanowires or nanotubes.

6. The transparent conductive film according to claim 1, wherein the nanoobjects comprise silver, copper, gold, platinum, palladium, nickel or carbon.

7. The transparent conductive film according to claim 1, wherein the nanoobjects have a diameter in the range from 1 to 100 nm and a length in the range from 1 to 500 m.

8. The transparent conductive film according to claim 1, wherein a difference in haze of the areas with lower conductivity and areas with higher conductivity is less than 0.5%.

9. A process for producing a patterned transparent conductive film according to claim 1, comprising: (a) applying an ink comprising electrically conductive nanoobjects and a binder on a substrate, thereby forming a first layer, wherein the amount of conductive nanoobjects is such that the first layer is conductive after drying; (b) drying the first layer; (c) applying a mixture comprising an insulating coating material or a precursor of an insulating coating material on parts of the first layer that will form the areas with lower conductivity, wherein the insulating coating material or the precursors form an insulating coating around the electrically conductive nanoobjects; and (d) rinsing and drying the coated substrate.

10. The process according to claim 9, wherein the electrically conductive nanoobjects are nanowires or nanotubes.

11. The process according to claim 9, wherein the electrically conductive nanoobjects comprise silver, copper, gold, platinum, palladium, nickel or carbon.

12. The process according to claim 9, wherein the electrically conductive nanoobjects have a diameter in the range from 1 to 100 nm and a length in the range from 1 to 500 m.

13. The process according to claim 9, wherein the ink comprising electrically conductive nanoobjects comprises from 0.01 to 0.5 wt-% electrically conductive nanoobjects, and from 0.02 to 2.5 wt-% binder and solvent.

14. The process according to claim 13, wherein the solvent is selected from the group consisting of water, an alcohol, a ketone, an ether, a hydrocarbon and an aromatic solvent.

15. The process according to claim 9, wherein the ink comprising conductive nanoobjects and binder is applied by spin coating, draw down coating, roll-to-roll coating, gravure printing, microgravure printing, screen-printing, flexoprinting or slot-die coating.

16. The process according to claim 9, wherein the ink comprising the electrically conductive nanoobjects is applied such that a wet thickness of the first layer is in the range from 100 nm to 40 m.

17. The process according to claim 9, wherein the drying in (b) and the drying in (d) each are carried out independently at a temperature in the range from 20 to 200 C. for 0.5 to 30 min.

18. The process according to claim 9, wherein the insulating coating material is selected from the group consisting of an insulating oxide, a complex insulating oxide and an insulating polymer.

19. The process according to claim 18, wherein the insulating coating material comprises an insulating oxide selected from the group consisting of SiO.sub.2, Al.sub.2O.sub.3, ZrO.sub.2 and zirconium silicate.

20. The process according to claim 18, wherein the insulating coating material comprises an insulating polymer selected from the group consisting of polystyrene, polyethylene, and fluorinated polyimide.

21. The process according to claim 9, wherein the insulating coating material is SiO.sub.2 and the precursor of the insulating coating material is silicon alkoxide or water glass.

22. The process according to claim 9, wherein the concentration of the insulating coating material or the precursor of the insulating coating material in the mixture comprising the insulating coating material or the precursor of the insulating coating material is in the range from 0.01 to 0.5 mol/l.

23. The process according to claim 9, wherein the mixture comprises a precursor of the insulating coating material in (c), and the precursor is transformed into the insulating coating material to form the insulating coating by a sol-gel-process, chemical vapor deposition, physical vapor deposition or atomic-layer deposition.

24. The process according to claim 9, wherein the mixture in (c) is applied by immersing, spin coating, draw down coating, roll-to-roll coating, gravure printing, microgravure printing, screen-printing, flexoprinting or slot-die coating.

Description

EXAMPLES

Manufacturing Example 1: Preparation of Silver Nanowire Films on Glass Substrates

(1) A styrene acrylic copolymer aqueous solution with 35 wt % solid content, available for example as Jonocryl 60 by BASF SE, is diluted in water to a concentration of 20 wt %. A copolymer of 2-ethylhexyl acrylate methyl methacrylate, available as Acronal LR9014 by BASF SE is diluted in water to a concentration of 10 wt %. A dispersion of 0.5 wt % silver nanowires in water, the diluted styrene acrylic copolymer aqueous solution and the diluted copolymer of 2-ethylhexyl acrylate methyl methacrylate are mixed in water so that the final concentration of the silver nanowires is 0.4 wt % and the mass ratio of styrene acrylic copolymer, copolymer of 2-ethylhexyl acrylate methyl methacrylate and nanowires is 4:3:3, respectively. The mixture is spin coated on glass substrate at 1000 rpm for 30 sec and dried for 5 min at 135 C. The sheet resistance is measured by a 4 point probe station (Lucas lab pro-4) and the optical properties are measured by BYK haze gard plus.

Manufacturing Example 2: Preparation of Silver Nanowire Films on Polycarbonate Substrates

(2) A styrene acrylic copolymer aqueous solution with 35 wt % solid content, available for example as Jonocryl 60 by BASF SE, is diluted in water to a concentration of 20 wt %. A copolymer of 2-ethylhexyl acrylate methyl methacrylate, available as Acronal LR9014 by BASF SE is diluted in water to a concentration of 10 wt %. A dispersion of 0.5 wt % silver nanowires in water, the diluted styrene acrylic copolymer aqueous solution and the diluted copolymer of 2-ethylhexyl acrylate methyl methacrylate are mixed in water so that the final concentration of the silver nanowires is 0.4 wt % and the mass ratio of styrene acrylic copolymer, copolymer of 2-ethylhexyl acrylate methyl methacrylate and nanowires is 4:3:3, respectively. The mixture is ball milled for 3 min to achieve homogenization. A conductive film is printed on an optical polycarbonate foil, for example commercially available under the product specification Makrofol DE 1-1 175 m from Bayer Material Science, using a draw-down bar with a wet thickness of 6 m and a coating speed of 5 cm/sec and afterwards dried for 5 min at 135 C. The sheet resistance and optical properties have been measured as in manufacturing example 1.

Manufacturing Example 3: Preparation of Silver Nanowire Films on Glass Substrates

(3) A dispersion of silver nanowires in water with an amount of 0.5 wt-% silver nanowires and a solution of 1 wt-% hydroxypropyl methylcellulose (HPMC) in water are mixed in water so that the final concentration of the silver nanowires ins 0.2 wt-% and the mass ratio of HPMC and silver nanowires is 2:1, respectively. The mixture is spin coated on glass substrate at 1000 rpm for 30 sec and dried for 5 min at 135 C. The sheet resistance is measured by a 4 point probe station (Lucas lap pro-4) and the optical properties are measured by BYK haze gard plus.

Examples 1, 2, and 3: SiO.SUB.2.-Coated Silver Nanowire Films on Glass Substrate

(4) Under continuous magnetic stirring, 0.4 ml of 28% ammonia solution in water and various amounts of Tetraethyl orthosilicate (TEOS) were consecutively added to a mixture of 20 ml of Isopropyl alcohol and 4 ml of water. Silver nanowire films on glass substrate produced according to manufacturing example 1 are immersed into this solution for a certain amount of time thereby forming a SiO.sub.2 coating on the nanowires, rinsed by deionized water and dried for 5 min at 135 C. The sheet resistance and optical properties before and after the coating with SiO.sub.2 are measured as in manufacturing example 1. The results are shown in table 1. Examples 1 and 2 show the results for different immersion times with the same amount of TEOS, example 3 is a comparative example without TEOS. In table 1 R.sub.sh means Sheet resistance, T means transmittance and H haze. before indicates the measuring of the substrate coated with a silver nanowire film before coating with SiO.sub.2 and after indicates the measuring after coating with SiO.sub.2.

(5) TABLE-US-00001 TABLE 1 TEOS Immersion Rsh Rsh T T H H amount time before after before after before after Example (ml) (min) (OPS) (OPS) (%) (%) (%) (%) 1 0.36 10 78 10 219 36 92.2 92.4 1.03 0.75 2 0.36 30 82 9 92.1 92.5 1.05 0.59 3 0 10 95 14 84 24 92.2 92.2 1.17 1.29

(6) From the examples can be seen that a longer immersion time with the same concentration of TEOS results in a much higher sheet resistance of the coated film. On the other hand, the immersion in an ammonia solution without TEOS shows no difference in sheet resistance. Further, coating with SiO.sub.2 does not have any effect on the transmittance of the patterned conductive film and the haze only has slightly lower values.

Examples 4, 5: SiO.SUB.2.-Coated Silver Nanowire Films on Polycarbonate Substrate

(7) Under continuous magnetic stirring, 0.4 ml of 28% ammonia solution in water and various amounts of Tetraethyl orthosilicate (TEOS) were consecutively added to a mixture of 20 ml of Isopropyl alcohol and 4 ml of water. On strips of silver nanowire films on polycarbonate substrate produced according to manufacturing example 2, fast drying silver paste was painted on the two ends as contact pads. The center region of strips is then immersed into the solution for 30 min, rinsed by deionized water and dried for 5 min at 135 C. The resistance between two silver contact pads before and after coating with SiO.sub.2 is measured by a Keithley source meter. The results are shown in Table 2, wherein example 5 is a comparative example. As in table 1 R.sub.sh means the sheet resistance and before and after indicate the measurements before and after coating with the TEOS comprising solution.

(8) In this example, the silver contact pads are placed outside the SiO.sub.2-coated region to show whether the electron flow is stopped across the SiO.sub.2-coated region.

(9) TABLE-US-00002 TABLE 2 TEOS Immersion Rsh Rsh amount time before after Example (ml) (min) (OPS) (OPS) 4 0.36 30 393 5 0 30 503 592

Example 6: SiO.SUB.2.-Coated Silver Nanowire Films on Glass Substrate

(10) Under continuous magnetic stirring, 0.4 ml of 28% ammonia solution in water and various amounts of Tetraethyl orthosilicate (TEOS) were consecutively added to a mixture of 20 ml of Isopropyl alcohol and 4 ml of water. Silver nanowire films on glass substrate produced according to manufacturing example 3 are immersed into this solution for 30 minutes thereby forming a SiO.sub.2 coating on the nanowires, rinsed by deionized water and dried for 5 min at 135 C. The sheet resistance and optical properties before and after the coating with SiO.sub.2 are measured as in manufacturing example 6. The results are shown in table 3. In table 3 R.sub.sh means Sheet resistance, T means transmittance and H haze. before indicates the measuring of the substrate coated with a silver nanowire film before coating with SiO.sub.2 and after indicates the measuring after coating with SiO.sub.2.

(11) TABLE-US-00003 TABLE 3 TEOS Immersion Rsh Rsh T T H H amount time before after before after before after Example (ml) (min) (OPS) (OPS) (%) (%) (%) (%) 6 0.36 30 129 8 92.4 94.2 0.47 0.52