COMPOSITION COMPRISING SILVER NANOWIRES AND DISPERSED POLYMER BEADS FOR THE PREPARATION OF ELECTROCONDUCTIVE TRANSPARENT LAYERS

Abstract

Described is a composition suitable for the preparation of an electroconductive transparent layer, said composition comprising silver nanowires and dispersed polymer beads.

Claims

1. A composition, comprising: (A) water, (B) electroconductive nanoobjects, said electroconductive nanoobjects (B) having two external dimensions in the range of from 1 nm to 100 nm and a third external dimension in the range of from 1 μm to 100 μm, wherein a weight fraction of said electroconductive nanoobjects (B) is in the range of from 0.01 wt.-% to 1 wt.-% based on the total weight of the composition, (C) dispersed in the water, particles of a polymer having a number average molecular weight of 25000 g/mol or higher, wherein said dispersed particles (C) have a mean diameter in the range of from 10 nm to 1000 nm, wherein the total weight fraction of said dispersed particles (C) is in the range of from 0.02 wt.-% to 5 wt.-%, based on the total weight of the composition.

2. The composition according to claim 1, wherein said electroconductive nanoobjects (B) have a length in the range of from 1 μm to 100 μm, and a diameter in the range of from 1 nm to 100 nm.

3. The composition according to claim 1, wherein said electroconductive nanoobjects (B) comprise one or more materials selected from the group consisting of silver, copper, gold and carbon.

4. The composition according to claim 1, wherein said electroconductive nanoobjects (B) are at least one member selected from the group consisting of nanowires and nanotubes.

5. The composition according to claim 1, wherein the ratio between the total weight of said electroconductive nanoobjects (B) and the total weight of said dispersed particles (C) is in the range of from 1:20 to 20:1.

6. The composition according to claim 1, further comprising one or more additional binding agents wherein the total weight fraction of said additional binding agents based on the total weight of the composition is equal to or less than the total weight fraction of said dispersed particles (C) based on the total weight of the composition.

7. The composition according to claim 1, comprising: (A) water, (B) silver nanowires, said silver nanowires (B) having a length in the range of from 10 μm to 50 μm and a diameter in the range of from 3 nm to 30 nm, wherein the weight fraction of said silver nanowires (B) is 0.5 wt.-% or less, based on the total weight of the composition, (C) dispersed in the water, particles of a polymer having a number average molecular weight of 30000 g/mol to 100000 g/mol, wherein said dispersed particles (C) have a mean diameter in the range of from 50 nm to 500 nm, wherein the weight fraction of said dispersed particles (C) is less than 2 wt.-%, based on the total weight of the composition, wherein the ratio between the total weight of said silver nanowires (B) and the weight of said dispersed particles (C) is in the range of from 1:5 to 5:1.

8. A method for preparing an electroconductive layer on a substrate, said method comprising: preparing or providing a composition according to claim 1, applying said composition to a surface of a substrate, removing constituents which at 25° C. and 101.325 kPa are liquid from said composition applied to said surface of said substrate to such extent that a layer is formed on said surface of said substrate; wherein said electroconductive layer has a light transmission of 80% or more measured according to ASTM D1003 (procedure A).

9. The method according to claim 8, wherein applying said composition to said surface of said substrate is carried out by at least one technique selected from the group consisting of spin coating, draw down coating, roll-to-roll coating, gravure printing, microgravure printing, screen-printing, flexoprinting and slot-die coating.

10. The method according to claim 8, wherein said substrate comprises a material selected from the group consisting of glass and organic polymers.

11. The method according to claim 8, wherein removing of those constituents which are liquid at 25° C. and 101.325 kPa from said composition applied to said surface of said substrate is achieved by subjecting said composition applied to said surface of said substrate to a temperature in the range of from 100° C. to 150° C. for a duration of 15 minutes or less.

12. An electroconductive layer, comprising: the following constituents which at 25° C. and 101.325 kPa are solid: (B) electroconductive nanoobjects, said electroconductive nanoobjects (B) having two external dimensions in the range of from 1 nm to 100 nm and a third external dimension in the range of from 1 μm to 100 μm, (C) particles of a polymer having a number average molecular weight of 25000 g/mol or higher, wherein said particles (C) have a mean diameter in the range of from 10 nm to 1000 nm; and wherein said electroconductive layer has a light transmission of 80% or more measured according to ASTM D1003 (procedure A).

13. The electroconductive layer according to claim 12, wherein said electroconductive layer exhibits a haze of 2% or less as measured according to ASTM D1003 (procedure A), and a sheet resistance of 1000 Ohm/square or less as measured by the four point probe.

14. The electroconductive layer according to claim 12, wherein said electroconductive layer exhibits one or more of a haze of 1% or less as measured according to ASTM D1003 (procedure A), a sheet resistance of 100 Ohm/square or less as measured by the four point probe, and a light transmission of 90% or more as measured according to ASTM D1003 (procedure A).

15. An article, comprising: a substrate having a surface; and an electroconductive layer according to claim 12 arranged on at least a portion of said surface of said substrate.

16. The article according to claim 15, wherein said electroconductive layer has a thickness in the range of from 10 nm to 1000 nm.

17. (canceled)

Description

EXAMPLES

[0159] 1. Examples of Layers on Polymer Substrates Obtained by Draw-Down Coating

[0160] 1.1 Compositions Comprising No Additional Binding Agent

[0161] An aqueous dispersion of silver nanowires (nanoobjects (B) as defined above) and an aqueous dispersion of beads (dispersed particles (C) as defined above) of a butyl acrylate-styrene copolymer (Acronal 296, average particle size 0.1 μm, commercially available from BASF) are mixed for the dispersing time given in table 1 so as to obtain an ink having a concentration of silver nanowires and a weight ratio of silver nanowires to dispersed polymer beads (C) as indicated in table 1.

[0162] The ink is applied to a polymer substrate using a draw-down bar (Erichsen K303) (wet thickness t=6 μm, coating speed v=2″/sec) to obtain a layer on said substrate. The layer is then dried at 135° C. for 5 min.

[0163] The sheet resistance Rsh given in Ohms/square (OPS) of the dried layer is measured by a four-point probe station (Lucas lab pro-4) and the optical properties are measured according to ASTM D1003 procedure A-Hazemeter by a haze-gard plus hazemeter (BYK Gardner). The results are compiled in table 1.

[0164] With regard to the optical properties, T refers to the light transmission and H refers to the haze of the substrate coated with the electroconductive layer. H(substrate subtracted) refers to the difference between the haze of the substrate coated with the electroconductive layer and the haze of the blank substrate (not coated with the electroconductive layer).

[0165] While all obtained layers have satisfying values of sheet resistance and transparence, it has been found that the haze value strongly depends on the dispersing time of the ink and is the lower the longer the ink dispersion time is.

TABLE-US-00001 TABLE 1 Silver nanowire Weight ratio Dispersing H(substrate Example concentration silver nanowires (B)/ time Rsh T H subtracted) Number (mg/ml) polymer beads (C) (min) (OPS) (%) (%) (%) 1 3.15 1:1 30 27.94 88.8 8.29 7.86 2 3.15 1:1 45 30.48 88.7 6.66 6.23 3 3.15 1:1 60 33.02 88.6 9.92 9.49 4 3.15 .sup. 1:0.5 30 22.86 87.7 5.25 4.82 5 3.15 .sup. 1:0.5 45 33.02 88.8 3.71 3.28

[0166] An aqueous dispersion of silver nanowires (nanoobjects (B) as defined above) and an aqueous dispersion of beads (dispersed particles (C) as defined above) of a copolymer of 2-ethylhexyl acrylate and methyl methacrylate (Acronal LR9014, average particle diameter 0.08 μm, commercially available from BASF) are mixed for a dispersing time of 30 minutes so as to obtain an ink having a concentration of silver nanowires of 3.85 mg/ml and a weight ratio of silver nanowires to dispersed polymer beads (C) as indicated in table 2.

[0167] The ink is applied to a polymer substrate using a draw-down bar (Erichsen K303) (wet thickness t=6 μm, coating speed v=2″/sec) to obtain a layer on said substrate. The layer is then dried at 135° C. for 5 min.

[0168] The sheet resistance Rsh given in Ohms/square (OPS) of the dried layer is measured by a four-point probe station (Lucas lab pro-4) and the optical properties (as defined above) are measured according to ASTM D1003 procedure A-Hazemeter by a haze-gard plus hazemeter (BYK Gardner). The results are compiled in table 2. All obtained layers had satisfying values of sheet resistance, transparency and haze.

TABLE-US-00002 TABLE 2 Weight ratio silver nanowires H (substrate Example (B)/polymer Rsh T H subtracted) number beads (C) (OPS) (%) (%) (%) 6 1:1 46.99 88.6 1.13 1 7 1:2 60.96 89.13 1.05 0.92 8 1:3 68.58 89.25 1.05 0.92 9 1:4 97.79 90.4 1.03 0.9 10 1:5 76.84 90.73 0.96 0.83

[0169] An aqueous dispersion of silver nanowires (nanoobjects (B) as defined above) and an aqueous dispersion of beads (dispersed particles (C) as defined above) of a copolymer of acrylates (Joncryl 95-E, commercially available from BASF) are mixed for a dispersing time of 30 minutes so as to obtain an ink having a concentration of silver nanowires and a weight ratio of silver nanowires to dispersed polymer beads (C) as indicated in table 3.

[0170] The ink is applied to a polymer substrate using a draw-down bar (Erichsen K303) (wet thickness t=6 μm, coating speed v=2″/sec) to obtain a layer on said substrate. The layer is then dried at 135° C. for 5 min.

[0171] The sheet resistance Rsh given in Ohms/square (OPS) of the dried layer is measured by a four-point probe station (Lucas lab pro-4) and the above-defined optical properties are measured according to ASTM D1003 procedure A-Hazemeter by a haze-gard plus hazemeter (BYK Gardner). The results are compiled in table 3. All obtained layers had satisfying values of sheet resistance, transparency and haze.

TABLE-US-00003 TABLE 3 Silver nanowire Weight ratio H(substrate Example concentration silver nanowires/ Rsh T H subtracted) Number (mg/ml) polymer beads (C) (OPS) (%) (%) (%) 11 3.47 2:1 45.72 89.5 0.88 0.75 12 3.47 1:1 52.07 89.95 0.95 0.82

[0172] An aqueous dispersion of silver nanowires (nanoobjects (B) as defined above) and an aqueous dispersion of beads (dispersed particles (C) as defined above) of a copolymer of 2-ethylhexyl acrylate methyl methacrylate (Acronal LR9014, commercially available from BASF) and beads (dispersed particles (C) as defined above) of a copolymer of acrylates (Joncryl 95-E, commercially available from BASF) are mixed for a dispersing time of 30 minutes in different ratios as indicated in table 4, so as to obtain an ink having a concentration of silver nanowires of 3.764 mg/mL and a weight ratio silver nanowires/Acronal LR9014/Joncryl 95-E as indicated in table 4. Both types of polymer beads are particles (C) as defined above)

[0173] The ink is applied to a polymer substrate using a draw-down bar (Erichsen K303) (wet thickness t=6 μm, coating speed v=2″/sec) to obtain a layer on said substrate. The layer is then dried at 135° C. for 5 min.

[0174] The sheet resistance Rsh given in Ohms/square (OPS) of the dried layer is measured by a four-point probe station (Lucas lab pro-4) and the above-defined optical properties are measured according to ASTM D1003 procedure A-Hazemeter by a haze-gard plus hazemeter (BYK Gardner). The results are compiled in table 4. All obtained layers had satisfying values of sheet resistance, transparency and haze.

TABLE-US-00004 TABLE 4 weight ratio Silver nanowire silver nanowires/ H(substrate Example concentration Acronal LR9014/ Rsh T H subtracted) Number (mg/ml) Joncryl 95-E (OPS) (%) (%) (%) 13 3.764 1:1:1 50.17 90.43 1.2 1.07 14 3.764 1:2:1 147.32 91.48 1.12 0.99

[0175] 1.2 Compositions Comprising an Additional Binding Agent

[0176] 1.2.1 Water-Soluble Styrene/(Meth)Acrylic Copolymers as the Additional Binding Agent

[0177] An aqueous dispersion of silver nanowires (nanoobjects (B) as defined above) and (with the exception of example 20) an aqueous dispersion of beads (dispersed particles (C) as defined above) of a copolymer of 2-ethylhexyl acrylate and methyl methacrylate (Acronal LR9014, commercially available from BASF) are mixed for a dispersing time of 30 minutes so as to obtain an ink having a concentration of silver nanowires and a weight ratio of silver nanowires polymer beads (C)/copolymer (D) as indicated in table 5.

[0178] Except for example 19, said dispersion of beads (dispersed particles (C) as defined above) comprises as an additional binding agent an amount a dissolved styrene acrylic copolymer (Joncryl 60, commercially available from BASF, copolymer (D) as defined above). The weight ratio silver nanowires (B)/polymer beads (C)/copolymer (D) for each ink is indicted in table 5.

[0179] In example 20 an aqueous dispersion of silver nanowires (nanoobjects (B) as defined above) and an aqueous solution of a styrene acrylic copolymer (Joncryl 60, commercially available from BASF, copolymer (D) as defined above) have been mixed for a dispersing time of 30 minutes so at to obtain an ink having a concentration of silver nanowires and a weight ratio silver nanowires (B)/copolymer (D) as indicated in table 5. Thus example 20 is a comparison example not according to the present invention because the ink of example 20 does not comprise any polymer beads (C).

[0180] The ink is applied to a polymer substrate using a draw-down bar (Erichsen K303) (wet thickness t=6 μm, coating speed v=2″/sec) to obtain a layer on said substrate. The layer is then dried at 135° C. for 5 min.

[0181] The sheet resistance Rsh given in Ohms/square (OPS) of the dried layer is measured by a four-point probe station (Lucas lab pro-4) and the above-defined optical properties are measured according to ASTM D1003 procedure A-Hazemeter by a haze-gard plus hazemeter (BYK Gardner). The results are compiled in table 5. All obtained layers had satisfying values of sheet resistance, transparency and haze.

TABLE-US-00005 TABLE 5 Weight ratio Silver nanowire silver nanowires/ H(substrate Example concentration polymer beads (C)/ Rsh T H subtracted) Number (mg/ml) copolymer (D) (OPS) (%) (%) (%) 15 4.71 1:4:1 45.09 90.2 1.37 1.24 16 4.21 1:4:1 46.36 90.30 1.26 1.13 17 3.81 1:4:1 52.71 90.48 1.15 1.02 18 3.48 1:4:1 64.77 90.5 1.09 0.96 19 3.89 1:5:0 71.76 90.45 1 0.87 20 3.89 1:0:5 139.07 89.35 0.71 0.58 21 3.89 2:5:5 53.98 89.58 1.21 1.08 22 3.89 4:15:5 55.88 89.93 1.14 1.01 23 3.89 6:25:5 59.06 90.03 1.11 0.98 24 3.89  6:5:25 81.92 89.33 0.81 0.68 25 3.89 11:50:5  61.60 90.13 1.05 0.92 26 3.48 1:4:1 64.77 89.98 1.01 0.88

[0182] 1.2.2 Fibers of Crystalline Cellulose as the Additional Binding Agent

[0183] An aqueous dispersion of silver nanowires (nanoobjects (B) as defined above) and an aqueous dispersion comprising beads (particles (C) as defined above) of a copolymer of acrylates (Joncryl 95E, commercially available from BASF) and fibers (E) of crystalline cellulose (commercially available from Celluforce) are mixed for a dispersing time of 30 minutes so as to obtain an ink having a concentration of silver nanowires and a weight ratio silver nanowires/polymer beads (C)/crystalline cellulose fibers (E) as indicated in table 6.

[0184] The ink is applied to a polymer substrate using a draw-down bar (Erichsen K303) (wet thickness t=6 μm, coating speed v=2″/sec) to obtain a layer on said substrate. The layer is then dried at 135° C. for 5 min.

[0185] The sheet resistance Rsh given in Ohms/square (OPS) of the dried layer is measured by a four-point probe station (Lucas lab pro-4) and the above-defined optical properties are measured according to ASTM D1003 procedure A-Hazemeter by a haze-gard plus hazemeter (BYK Gardner). The results are compiled in table 6. All obtained layers had satisfying values of sheet resistance, transparency and haze.

TABLE-US-00006 TABLE 6 Weight ratio silver nanowires (B)/ Silver nanowire polymer beads (C)/ H(substrate Example concentration crystalline cellulose Rsh T H subtracted) No (mg/ml) fibers (E) (OPS) (%) (%) (%) 27 3.439 1:1:1 78.74 89.58 0.87 0.74 28 3.870 2:4:1 45.72 89.68 1.08 0.95

[0186] An aqueous dispersion of silver nanowires (nanoobjects (B) as defined above) and an aqueous dispersion comprising beads (particles (C) as defined above) of a copolymer of 2-ethylhexyl acrylate and methyl methacrylate (Acronal LR9014, commercially available from BASF) and fibers (E) of crystalline cellulose (commercially available from Celluforce) are mixed for a dispersing time of 30 minutes so as to obtain an ink having a concentration of silver nanowires and a weight ratio of silver nanowires/polymer beads (C)/crystalline cellulose fibers (E) as indicated in table 7.

[0187] The ink is applied to a polymer substrate using a draw-down bar (Erichsen K303) (wet thickness t=as indicated in table 7, coating speed v=2″/sec) to obtain a layer on said substrate. The layer is then dried at 135° C. for 5 min.

[0188] The sheet resistance Rsh given in Ohms/square (OPS) of the dried layer is measured by a four-point probe station (Lucas lab pro-4) and the above-defined optical properties are measured according to ASTM D1003 procedure A-Hazemeter by a haze-gard plus hazemeter (BYK Gardner). The results are compiled in table 7. All obtained layers had satisfying values of sheet resistance, transparency and haze.

TABLE-US-00007 TABLE 7 Weight ratio silver nanowires (B)/ Silver nanowire polymer beads (C)/ Wet H(substrate Example concentration crystalline cellulose thickness Rsh T H subtracted) No. (mg/ml) fibers (E) (μm) (OPS) (%) (%) (%) 29 4.286 1:1:1 4 184.79 90.2 0.82 0.69 30 4.286 1:1:1 6 49.53 90.35 1.25 1.12 31 4.286 1:1:1 8 41.28 90.6 1.49 1.36 32 3.427   1:2:0.5 6 111.76 90.98 0.97 0.84 33 3.427 1:1:1 6 55.88 90.33 1.04 0.91

[0189] 2. Examples of Layers on Glass Substrates Obtained by Spin-Coating

[0190] An aqueous dispersion of silver nanowires (nanoobjects (B) as defined above) and an aqueous dispersion of beads (particles (C) as defined above) of a copolymer of acrylates (Joncryl 95 or 95-E, commercially available from BASF) are mixed for a dispersing time of 30 minutes so as to obtain an ink having a concentration of silver nanowires and a weight ratio of silver nanowires to dispersed polymer beads (C) as indicated in table 8.

[0191] The ink is spin-coated (Smart Coater 100) on glass substrates at various spin speeds (see table 9) for 60 sec to generate layers with different wet thickness. The layers are then dried at 130° C. for 5 min.

[0192] The sheet resistance Rsh given in Ohms/square (OPS) of the dried layer is measured by a four-point probe station (Lucas lab pro-4) and the optical properties as defined above are measured according to ASTM D1003 procedure A-Hazemeter by a haze-gard plus hazemeter (BYK Gardner). The results are compiled in table 8.

[0193] The applied amount of ink is the same in all spin coating examples. The thickness of the dried layer depends on the spin speed when using an ink of a fixed concentration. At high spin speeds there is more ink flowing away from the substrate. Thus, variation of the spin speed can be used to vary the obtained sheet resistance and optical properties (as defined above) so as to match the requirements of different applications of transparent electroconductive layers. High spin speeds allow for generating very thin layers having high light transmission and low haze, but rather high sheet resistance. In turn, low spin speeds allow for generating thicker layers having a low sheet resistance, but a lower light transmission and a higher haze.

TABLE-US-00008 TABLE 8 Silver nanowire Weight ratio Spin H(substrate Example concentration silver nanowires/ speed Rsh T H subtracted) Number (mg/ml) polymer beads (C) (rpm) (OPS) (%) (%) (%) 34 4 1:2 1000 26 90.7 1.5 1.33 35 4 1:2 1500 38 90.6 1.47 1.3 36 4 1:2 2000 44 91.6 1.16 0.99 37 4 1:2 2500 98 92.4 0.67 0.5 38 4 1:2 3000 107 92.6 0.56 0.39

[0194] An aqueous dispersion of silver nanowires (nanoobjects (B) as defined above) and an aqueous dispersion of beads (dispersed particles (C) as defined above) of a butyl acrylate-styrene copolymer (Acronal 296, commercially available from BASF) are mixed for a dispersing time of 30 minutes so as to obtain an ink having a concentration of silver nanowires and a weight ratio of silver nanowires to dispersed polymer beads (C) as indicated in table 9.

[0195] The ink is spin-coated (Smart Coater 100) on glass substrates at 1000 rpm for 60 sec to generate layers with different wet thickness, due to the different concentration of solid constituents. The layers are then dried at 130° C. for 5 min.

[0196] The sheet resistance Rsh given in Ohms/square (OPS) of the dried layer is measured by a four-point probe station (Lucas lab pro-4) and the optical properties as defined above are measured according to ASTM D1003 procedure A-Hazemeter by a haze-gard plus hazemeter (BYK Gardner). The results are compiled in table 9.

TABLE-US-00009 TABLE 9 Silver nanowire Weight ratio H(substrate Example concentration silver nanowires (B)/ Rsh T H subtracted) Number (mg/ml) polymer beads (C) (OPS) (%) (%) (%) 39 0.5 1:1 196 93.1 0.94 0.64 40 1.0 1:1 101 92.4 1.35 1.05 41 1.5 1:1 61 91.8 2.18 1.88 42 2.0 1:1 44 91.1 2.83 2.53 43 3.0 1:1 32 90.2 3.86 3.56