Patterning of a composition comprising silver nanowires

Abstract

The present invention relates to the production of a layer structure, comprising the following process steps: i) coating a substrate with a composition at least comprising silver nanowires and a solvent; ii) at least partial removal of the solvent, thereby obtaining a substrate that is coated with an electrically conductive layer, the electrically conductive layer at least comprising the silver nanowires; iii) bringing into contact selected areas of the electrically conductive layer with an etching composition, thereby reducing the conductivity of the electrically conductive layer in these selected areas, wherein the etching composition comprises an organic compound capable of releasing chlorine, bromine or iodine, a compound containing hypochloride, a compound containing hypo-bromide or a mixture of at least two of these compounds. The invention also relates to a layer structure obtainable by this method, a layer structure, the use of a layer structure, an electronic component and the use of an organic compound.

Claims

1. A method for producing a layer structure, comprising the process steps: i) coating a substrate with a composition comprising silver nanowires, a sulfonated polymer, a conductive polymer and a solvent, wherein the conductive polymer is a polythiophene; ii) partially removing the solvent, thereby obtaining a substrate that is coated with an electrically conductive layer, the electrically conductive layer comprising the silver nanowires, the sulfonated polymer and the conductive polymer; and iii) bringing into contact selected areas of the electrically conductive layer with an etching composition, thereby reducing the conductivity of the electrically conductive layer in these selected areas, wherein the etching composition comprises an organic compound capable of releasing chlorine, bromine or iodine, a compound containing hypochloride, a compound containing hypobromide or a mixture of at least two of these compounds; wherein the surface resistance of the selected areas that have been brought into contact with the etching composition in step iii) is at least 10 times greater than the surface resistance of the layer provided in process step ii); and wherein the color difference (?E) between the selected areas that have been brought into contact with the etching composition in step iii) and the electrically conductive layer provided in step ii) is at most 4.5.

2. The method according to claim 1, wherein the silver nanowires in the composition used in process step i) have a length of from 1 ?m to 200 ?m, a diameter of from 20 nm to 1,300 nm and an aspect ratio (length/diameter) of at least 5.

3. The method according to claim 1, wherein the silver nanowires in the composition used in process step i) are obtained by a process comprising the process steps: a) providing a reaction mixture comprising a polyol, an organic chemical which is adsorbed on to a silver surface, a chemical which forms a halide and/or one which forms a pseudohalide, wherein the chemical which forms a halide is a salt of one of the halides Cl.sup.?, Br.sup.? and/or I.sup.? and wherein the chemical which forms a pseudohalide is a salt of one of the pseudohalides SCN.sup.?, CN.sup.?, OCN.sup.? and/or CNO.sup.?, a chemical which forms a redox pair, chosen from the group consisting of bromine, iodine, vanadium and mixtures thereof, and a silver salt, and b) heating the reaction mixture to a temperature of at least 100? C.

4. The method according to claim 1, wherein the sulfonated polymer in the composition used in process step i) is polystyrene sulfonic acid (PSS).

5. The method according to claim 1, wherein the conductive polymer is present in the form of a complex formed from the polythiophene and the sulfonated polymer.

6. The method according to claim 5, wherein the conductive polymer is poly(3,4-ethylenedioxythiophene) (PEDOT) and is present in the form of a PEDOT/PSS-complex.

7. The method according to claim 1, wherein the organic compound capable of releasing chlorine, bromine or iodine comprises at least one structural element (II) ##STR00007## wherein Hal is a halogen selected from the group consisting of chlorine, bromine and iodine, Y is selected from N, S and P, and X.sub.1 and X.sub.2 can be the same or different and each denote respectively a halogen, a carbon atom or a sulphur atom, and wherein one or more further atoms can optionally be bonded to X.sub.1 and X.sub.2.

8. The method according to claim 7, wherein the organic compound capable of releasing chlorine or bromine comprises at least two structural elements (II) in which Hal denotes a chlorine atom or a bromine atom and Y denotes nitrogen, wherein the at least two structural elements (II) can optionally be different from one another.

9. The method according to claim 8, wherein the organic compound capable of releasing chlorine or bromine comprises the structural element (III) ##STR00008## in which a chlorine atom or a bromine atom is bonded to at least two of the nitrogen atoms.

10. The method according to claim 9, wherein the organic compound capable of releasing chlorine or bromine is sodium dichloroisocyanurate, sodium dibromoisocyanurate, tribromoisocyanuric acid or trichloroisocyanuric acid.

11. The method according to claim 1, wherein the etching composition used in process step iii) comprises the organic compound capable of releasing chlorine, bromine or iodine, the compound containing hypochloride, the compound containing hypobromide or the mixture of at least two of these compounds in a concentration in a range from 0.01 to 50 wt.-%, relative to the total weight of the etching composition.

12. The method according to claim 1, wherein the bringing into contact of the electrically conductive layer with the etching composition is performed by dipping the electrically conductive layer into the etching composition or by printing the electrically conductive layer with the etching composition.

13. The method according to claim 1, wherein the method comprises as a further process step: iv) washing the electrically conductive layer brought into contact with the etching composition.

14. The method of claim 1, wherein step iii) is performed without affecting the optical appearance of the selected areas.

15. The method of claim 1, wherein the surface resistance of the selected areas that have been brought into contact with the etching composition in step iii) is at least 100 times greater than the surface resistance of the layer provided in process step ii).

16. The method of claim 1, wherein the surface resistance of the selected areas that have been brought into contact with the etching composition in step iii) is at least 1,000 times greater than the surface resistance of the layer provided in process step ii).

17. The method of claim 1, wherein the surface resistance of the selected areas that have been brought into contact with the etching composition in step iii) is at least 10,000 times greater than the surface resistance of the layer provided in process step ii).

18. The method of claim 1, wherein the surface resistance of the selected areas that have been brought into contact with the etching composition in step iii) is at least 100,000 times greater than the surface resistance of the layer provided in process step ii).

19. The method of claim 1, wherein the color difference (?E) between the selected areas that have been brought into contact with the etching composition in step iii) and the electrically conductive layer provided in step ii) is at most 3.0.

20. The method of claim 1, wherein the color difference (?E) between the selected areas that have been brought into contact with the etching composition in step iii) and the electrically conductive layer provided in step ii) is at most 1.5.

Description

(1) The invention is now described in more detail by reference to figures, test methods and non-limiting examples.

(2) FIG. 1 shows a cross-section of the structure of a layer structure 1 according to the invention, for example an antistatic film, in general form. On a substrate 2 a coating is applied which encompasses areas 3 with a surface resistance R and areas 4 with a surface resistance at least 10 times greater than R. FIG. 2 shows the same layer structure 1 from above.

TEST METHODS

(3) Determining the Surface Resistance

(4) The determination was carried out by means of a so called four-point probe measurement as described for instance in U.S. Pat. No. 6,943,571 B1. The values are given in ?/square.

(5) Determining the Colour Values L, a and b and the Transmission

(6) The measurement of the transmission spectra of the coated PET films is carried out on a Lambda 900 two-channel spectrophotometer from Perkin Elmer. The instrument is fitted with a 15-cm photometer sphere, measurements are carried out in the sphere, to ensure that no interferences of the scattered light are detected. So the here presented values for transmission include also the scattered light or to this end transmission is 1-absorption.

(7) Spectra were recorded in the visible range of the spectra from 320 nm to 780 nm in 5 nm steps. There is no sample in the reference beam, so the spectra are recorded against air.

(8) First transmission of an uncoated substrate is measured as a reference, as a substrate Melinex 506 films with a film thickness of 175 ?m are used. Subsequently the coated substrates were measured.

(9) From the spectra, the standard colour value Y (brightness) of the sample was calculated according to DIN 5033, on the basis of a 10?-abserver and the light type D65. The internal transmission was calculated from the ration of brightness of the substrate with the coating (Y) to that without the coating (Y.sub.0) as follows:
Internal transmission corresponds to Y/Y.sub.0?100 percent.

(10) For the sake of convenience in the following transmission means the internal transmission.

(11) Using the software WinCol Version 1.2 supplied by the instrument manufacturer the colour evaluation of the transmission spectra was done. Here the CIE tristimulus values (standard colour values) X, Y and Z of the transmission spectrum in the wavelength range 380 nm to 780 nm are calculated in accordance with ASTM 308-94a and DIN 503. From the standard colour values the CIELAB coordinates L*, a* and b* are calculated in accordance with ASTM 308-94a and DIN 5033.

EXAMPLES

Example 1

(12) Silver nanowires (AgNW) were synthesized using the polyol synthesis as described for example in WO-A-2012/022332. 50 g of the obtained mixture were mixed with 130 mL of acetone. The mixture was stirred for 30 min The supernatant solution was discarded and a precipitate is obtained.

(13) The precipitate was mixed with 20 g of water and shaken. The mixture is then centrifuged (2500 rpm/20 min) The supernatant is again discarded. The mixing with water, shaking, centrifugation and sedimentation is repeated four times.

Example 2

(14) Formulation Clevios PH 1000 with silver nanowires for transparent conductive coatings are prepared. 2.77 g silver nanowires (2.7% silver content gravimetrically, 75 mg silver) were mixed with 5.71 g of water, 7.85 g Clevios PH 1000 (86 mg PEDOT/PSS, Heraeus Precious Metals GmbH & Co. K G, Leverkusen), 0.755 g dimethylsulfoxide (DMSO, ACS reagent, Sigma Aldrich, Munich) and 50 ?L Triton X100 (Sigma Aldrich, Munich). The formulation was coated on Melinex 506 films (P?tz GmbH+Co. Folien K G. Taunusstein) using a 6 ?m wet-film thickness doctor blade (Erichsen K Hand Coater 620). Coatings were dried for 5 min at 120? C.

Example 3

(15) Coated films from Example 2 were cut into pieces measuring approximately 5?10 cm. The lower half of the stripes were dipped into different water based etching solutions for 2 min, subsequently rinsed in a water bath for 1 min and dried for 5 min at 120? C. The surface resistivity was measured before and after treatment by the four-point probe technique. The results are summarized in Table 1.

(16) TABLE-US-00001 TABLE 1 Etching results Surface resistance Surface resistance Untreated after treatment Etchant [?/square] [?/square] Water 84 102 KMnO.sub.4 [1%] 88 n.d. KMnO.sub.4 [0.1%] 79 5663 KMnO.sub.4 [0.01%] 86 1595 HNO.sub.3 [10%] 95 109 CuCl.sub.2 [7%] 91 834 H.sub.2O.sub.2 [10%] 113 1100 Dichloroisocyanuric 91 n.d. acid [10%] n.d. non detectable (>1 ? 10.sup.8 ?/square)

(17) The color coordinates in the L*a*b coordinates system were determined on the etched and untreated pieces of the films. The differences (?L, ?a* and ?b*) are shown in table 2.

(18) TABLE-US-00002 TABLE 2 L*a*b values Etchant ?L* ?a* ?b* Water 0.05 0 0.03 KMnO.sub.4 [1%] 2.45 0.74 2.72 KMnO.sub.4 [0.1%] 1.44 0.4 1.8 KMnO.sub.4 [0.01%] 1.03 0.32 1.31 HNO.sub.3 [10%] 0.1 0 0.07 CuCl.sub.2 [7%] 0.16 0.1 0.29 H.sub.2O.sub.2 [10%] 0.34 0.1 0.26 Dichloroisocyanuric 0.21 0.18 0.05 acid [10%]

(19) Furthermore, the transmission (Y D65/10? value) of the etched and untreated pieces of the films was measured. The results are shown in table 3.

(20) TABLE-US-00003 TABLE 3 transmission transmission transmission Etchant untreated after treatment Water 97.7 97.6 KMnO.sub.4 [1%] 97.15 91.07 KMnO.sub.4 [0.1%] 97.32 93.49 KMnO.sub.4 [0.01%] 97.61 94.73 HNO.sub.3 [10%] 97.3 97.5 CuCl.sub.2 [7%] 97.3 97.6 H.sub.2O.sub.2 [10%] 97.4 98.3 Dichloroisocyanuric 97.4 97.9 acid [10%]

(21) As can be seen from the results shown in tables 1, 2 and 3, using organic compound capable of releasing chlorine, such as Dichloroisocyanuric acid, for etching conductive layers containing silver nanowires leads to a remarkable reduction of the surface resistance (see table 1) without significantly affecting the optical properties of the etched areas (see tables 2 and 3). Using the etching compounds of the prior art for etching conductive layers comprising silver nanowires, such as CuCl.sub.2, HNO.sub.3, H.sub.2O.sub.2 or KMnO.sub.4, either leads to a significant deterioration of the optical properties (as can be seen for KMnO.sub.4 in tables 2 and 3) or to a comparatively low reduction of the surface resistance (as can be seen for CuCl.sub.2, HNO.sub.3 and H.sub.2O.sub.2 in table 1).

Example 4

(22) Films that have been etched with a 10% solution of dichloroisocyanuric acid were stored in a climate cabinet at 85? C. and 85% humidity for 2 or 4 days and the surface resistivity was measured again. For all samples the surface resistivity of the etched part was not detectable (>1?10.sup.8 ?/square).