TRANSPARENT CONDUCTIVE LAYER, A FILM COMPRISING THE LAYER, AND A PROCESS FOR ITS PRODUCTION

Abstract

The invention relates to a transparent conductive layer comprising non-conductive areas and conductive areas, wherein the conductive areas comprise an FIG. 1 interconnected network of electrically conductive nanoobjects and in the non-conductive areas the nanoobjects are converted into particles and wherein the thickness of the conductive areas and the non-conductive areas differs less than 10 nm. The invention further relates to a process for producing a patterned transparent conductive film, the film comprising a substrate and a transparent conductive layer, and to a process for producing the patterned transparent conductive film.

Claims

1-18. (canceled)

19. A transparent conductive layer, comprising: non-conductive areas and conductive areas, wherein the conductive areas comprise an interconnected network of electrically conductive nanoobjects and in the non-conductive areas the nanoobjects are converted into particles, and wherein the thickness of the conductive areas and the non-conductive areas differs less than 10 nm.

20. The transparent conductive layer according to claim 19, wherein the ratio of sheet resistance in the non-conductive areas and the conductive areas is larger than 1000.

21. The transparent conductive layer according to claim 19, wherein the difference in light transmission of the non-conductive areas and the conductive areas is less than 5%.

22. The transparent conductive layer according to claim 19, wherein the difference in haze of the non-conductive areas and the conductive areas is less than 0.5%.

23. The transparent conductive layer according to claim 19, wherein the electrically conductive nanoobjects are nanowires or nanotubes.

24. The transparent conductive layer according to claim 19, wherein the electrically conductive nanoobjects are made of silver, copper, gold, platinum, palladium, nickel or carbon.

25. The transparent conductive layer according to claim 19, 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 100 μm

26. The transparent conductive layer according to claim 19, wherein the particles generated during conversion remain at the same position at which the nanowires have been.

27. A patterned transparent conductive film, comprising: a substrate, and a conductive layer according to claim 19 on the substrate.

28. The patterned transparent conductive film according to claim 27, wherein the substrate is optically transparent.

29. The patterned transparent conductive film according to claim 27, wherein the substrate is made of glass, polycarbonate, polyethylene terephthalate, cyclic olefin polymer, polyimide, or polymethyl methacrylate.

30. A process for producing a patterned transparent conductive film according to claim 27, comprising: (a) applying of an ink comprising conductive nanoobjects and a binder on a substrate, forming a layer; (b) drying the layer; (c) patterning the layer by irradiating with a laser, the pattern comprising conductive areas and non-conductive areas, wherein in the non-conductive areas the conductive nanoobjects are converted into particles.

31. The process according to claim 30, wherein the ink comprising conductive nanowires and binder is applied by spin coating, draw down coating, roll-to-roll coating, gravure printing, microgravure printing, screen-printing, flexoprinting and slot-die coating.

32. The process according to claim 30, wherein the ink applied to the substrate comprises 0.01 to 1 wt % electrically conductive nanoobjects, 0.02 to 5 wt % binder and solvent.

33. The process according to claim 32, wherein the solvent is at least one selected from the group consisting of water, alcohols, ketones, ethers, hydrocarbons and aromatic solvents.

34. The process according to claim 30, wherein the drying of the layer is carried out at a temperature in the range from 20 to 200° C. for 0.5 to 30 min.

35. The process according to claim 30, wherein the drying of the layer is carried out in an atmosphere comprising air, nitrogen or argon.

36. The process according to claim 30, wherein the binder is selected from the group consisting of hydropropyl methyl cellulose, crystalline cellulose, poly(meth)acrylates, copolymers of acrylates and methacrylates, copolymers of styrene and (meth)acrylates, carboxymethyl cellulose, poly acrylamide, polyvinylalcohol, polyvinylpyrrolidone, polystyrenesulfonic acid, dextran and mixtures thereof.

Description

[0059] The invention is hereinafter further illustrated by means of examples. Results additionally are shown in the figures.

[0060] In the figures:

[0061] FIG. 1 shows a grid pattern;

[0062] FIG. 2(a) shows an optical image with a rectangle indicating AFM scanned area;

[0063] FIG. 2(b) shows an AFM height image at 100 μm×100 μm;

[0064] FIG. 2(c) shows AFM profile analysis.

[0065] FIG. 3 shows a SEM image of a laser treated silver nanowire layer;

[0066] FIG. 4 shows a detail of the laser treated silver nanowire layer of FIG. 3.

EXAMPLES

Example 1

Preparation of Silver Nanowire Layers on Glass Substrates

[0067] Hydropropyl methyl cellulose is dissolved in water at a concentration of 1 wt %. The dissolved hydropropyl methyl cellulose and a dispersion of silver nanowires in water (0.5 wt %) are mixed in water so that the final concentration of silver nanowires is 0.25 wt % and the mass ratio of hydropropyl methyl cellulose and silver nanowires is 1:2, respectively. Nanowires are obtainable for example from Seashell Technologies (San Diego, Calif.). The mixture is spin coated on glass substrates at 2000 rpm for 30 sec. The layers are then dried at 130° C. for 5 min. 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.

Example 2

Preparation of Silver Nanowire Layers on Polycarbonate Substrates

[0068] A styrene acrylic copolymer aqueous solution with 35% solid content, available as Joncryl® 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 silver nanowires in water (0.5 wt %), 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 silver nanowires is 4:3:3, respectively. The mixture is ball milled for 3 min to achieve homogenization. A conductive layer is printed on an optical polycarbonate foil, for example commercially available under the product specification Makrofol® DE 1-1 175 μm from Bayer Material Science, using a draw-down bar (wet thickness t=6μm, coating speed v=2″/sec) was dried for 5 min at 135° C. Sheet resistance and optical properties are measured as in Example 1.

Example 3

Laser Patterning of Silver Nanowire Layers on Glass—Grid Pattern

[0069] A silver nanowire layer prepared according to example 1 is patterned by laser according to a grid pattern as shown in FIG. 1. The laser is a Rofin® model F20 operating at I=1070 nm, pulse repetition rate 60 kHz, and laser power 3 W. The width of the focused beam on the substrate was about 30 μm. The distance between adjacent lines is 1.5 mm. The laser was scanned across the substrate at a speed of about 600 mm/sec. The patterned layer is examined under scanning electron microscope (SEM). The SEM images are shown in FIGS. 3 and 4, wherein FIG. 4 shows the detail which is marked by the rectangle in FIG. 3.

[0070] The laser traces 1 are roughly 30 μm wide. The silver nanowires 5 in the non-treated regions 4 are intact while those in the laser traces 1 are converted to silver particles 6. The particles 6 have similar diameters to the silver nanowires 5 and they stay where the nanowires were before the laser treatment.

[0071] FIG. 2(a) shows an optical image with a rectangle indicating a 100 μm×100 μm AFM scanned area. FIGS. 2(b) and 2(c) show the AFM height image and profile analysis, wherein FIG. 2(b) shows the detail which is marked by a rectangle in FIG. 2(a). The red triangles in FIGS. 2 (b) and 2(c) indicate the two locations where the height of the film was measured. As can be seen in FIG. 2(c), the thickness of the conductive areas and the non-conductive areas differs by 3.8 nm.

Example 4

Optical Property Change of Silver Nanowire layers on Glass After Laser Treatment

[0072] In order to measure the optical property change after laser treatment, silver nanowire layers on 25 cm-by-25 cm size are prepared according to example 1 on glass and the entire surface is processed by laser. An Infrared fiber laser is used. The incident laser energy is varied by using different laser power, pulse repetition rate and velocity. After laser treatment, the sheet resistance is measured as in example 1. The results are shown in tables 1.1 and 1.2.

TABLE-US-00001 TABLE 1.1 Laser Pulse repetition R.sub.sh R.sub.sh power rate Velocity before after Sample # (W) (Hz) (mm/s) (OPS) (OPS) 1 3 90k 600 84 ± 3 ~1000 2 3 80k 600 77 ± 3 ∞ 3 3 70k 600 81 ± 1 ∞ 4 3 50k 600 74 ± 5 ∞ 5 3 90k 550 81 ± 1 ∞ 6 3.2 90k 600 77 ± 6 ∞

TABLE-US-00002 TABLE 1.2 T H before T after before H after Sample # (%) (%) ΔT % (%) (%) ΔH 1 92.1 91.7 0.4 0.75 0.75 ~0 2 92.0 91.5 0.5 1.04 1.03 0.01 3 92.1 91.3 0.8 0.83 0.85 0.02 4 92.0 89.4 0.6 0.84 0.96 0.12 5 92.1 91.6 0.5 0.83 0.82 0.01 6 92.1 91.6 0.5 0.87 0.90 0.03

[0073] Samples 1 through 4 are treated with the same laser power and velocity but different pulse repetition rate. Lower pulse repetition rate leads to higher incident laser energy. Sample 1 shows a sheet resistance (R.sub.sh) of about 1000 OPS indicating the incident laser energy is too low to break down the percolating network completely. Samples 2 and 3 show a sheet resistance which exceeded the measurement range and was too high to be measured. The optical properties change very little after the laser treatment, satisfying the requirements. The incident laser energy for sample 4 is higher. As a result, the transmission T and the haze H change is also higher (2.6% and 0.12%, respectively).

[0074] Samples 5 and 6 are treated with the same pulse repetition rate as sample 1 but with different velocity and laser power, respectively. Lower velocity or higher laser power leads to higher incident laser energy. Therefore, both sample 5 and 6 have higher incident laser energy than sample 1. Both samples show no conductance and the optical properties change very little after the laser treatment, satisfying the requirements.

Example 5

Optical Property Change of Silver Nanowire Layers on Polycarbonate After Laser Treatment

[0075] A sheet of silver nanowire layer on polycarbonate is prepared according to example 2. In order to measure the optical property change after laser treatment, a piece of 25 cm-by-25 cm size is cut and the entire surface of this piece is processed by the laser. After laser treatment, the sheet resistance is measured as in example 1. Results are shown in Tables 2.1 and 2.2.

TABLE-US-00003 TABLE 2.1 Laser Pulse repetition Rsh Rsh power rate Velocity before after Sample # (W) (Hz) (mm/s) (OPS) (OPS) 7 2 100k 2000 58 ± 3 ∞

TABLE-US-00004 TABLE 2.2 T H before T after before H after Sample # (%) (%) ΔT % (%) (%) ΔH % 7 90.3 89.4 0.9 1.16 1.14 0.02

[0076] At this incident laser energy, sample 7 shows no conductance and and optical properties change very little after the laser treatment, satisfying the requirements.