Conductive ink

Abstract

A method of forming transparent electrodes using printable conductive ink containing conductive materials dispersed in a viscous liquid which upon printing and thermal treatment will vaporise fully leaving behind the conductive material only. The viscous liquid acts as a medium by which conductive material dispersions are made processable for use in various printing techniques, allowing conductive patterns to be printed onto substrates (e.g. plastics, glass, metals, ceramics).

Claims

1. A method of producing a printable conductive ink, comprising: forming a mixture of a first composition, comprising at least one amine, wherein the at least one amine is a primary amine having a total carbon count of 1, 2, 3, 4, or 5 or wherein the at least one amine is a carbon-bridged diamine having a carbon count of 1, 2, 3, 4, 5, 6, 7, 8, or 9; a second composition, comprising at least one carboxylic acid, wherein the at least one carboxylic acid has a total carbon count of 1, 2, 3, 4, or 5 or wherein the at least one carboxylic acid is a carbon-bridged dicarboxylic acid with a total carbon count of 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, or 16; and a conductive material, wherein the conductive material comprises silver nanowires, wherein the silver nanowires are coated with a dispersant prior to addition of the first and second compositions.

2. The method according to claim 1, wherein the conductive material is mixed with the first composition prior to mixing of the second composition.

3. The method according to claim 1, wherein the conductive material is mixed with the second composition prior to mixing of the first composition.

4. The method according to claim 1, wherein the conductive material is mixed with the first and second compositions after mixing of the first and second compositions.

5. The method according to claim 1, wherein the at least one carboxylic acid has a total carbon count of 1, 2, 3, 4, or 5.

6. The method according to claim 1, wherein the at least one carboxylic acid has a total carbon count less than 6.

7. The method according to claim 1, wherein the at least one carboxylic acid is a carbon-bridged dicarboxylic acid with a total carbon count of 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, or 16.

8. The method according to claim 1, wherein the at least one carboxylic acid is a carbon-bridged dicarboxylic acid with a total carbon count less than 17.

9. The method according to claim 1, wherein mixing the first and second compositions is an exothermic reaction, the method further comprising a step of allowing the mixture to cool to form a transparent viscous liquid prior to adding the conductive material.

10. The method according to claim 1, comprising mixing equimolar quantities of amine and carboxylic acid.

11. The method according to claim 1, comprising the step of mixing from 0.2 to 2 relative molar amounts of carboxylic acid with amine.

12. The method according to claim 1, wherein the dispersant is polyvinylpyrrolidone.

13. The method according to claim 1, wherein the conductive material is added to the mixture at a concentration of from 5 to 15 weight percent relative to the total weight of mixture.

14. The method according to claim 1, wherein the conductive material is added with stirring.

15. The method according to claim 1, wherein the mixture is sonicated after addition of the conductive material.

16. The method according to claim 15, wherein the mixture is sonicated for at least 30 minutes.

17. The method according to claim 16, wherein the mixture is stirred for at least an hour following sonication.

18. The method according to claim 1, comprising the step of adding a polymeric additive to the mixture.

19. A method of forming printed conductive electrodes, comprising: printing a pattern onto a surface of a substrate using conductive ink produced according to claim 1, wherein the conductive ink comprises a liquid component and a conductive material component; and heating the substrate to vaporize the liquid component of the ink to leave the conductive material component adhered to the surface of the substrate.

20. The method according to claim 19, wherein the substrate is heated to a temperature from 100 C. to 150 C.

21. The method according to claim 19, comprising the step of coating the substrate with a polymer prior to printing the electrode.

22. The method according to claim 21, wherein the substrate is coated with polyvinylpyrrolidone.

23. The method according to claim 19, wherein pressure is applied to the printed conductive electrode.

24. The method according to claim 19, wherein photonic sintering is applied to the printed conductive electrode.

25. A printable conductive ink manufactured according to the method of claim 1.

26. A printed conductive electrode manufactured according to the method of claim 19.

27. The printed conductive electrode according to claim 26, wherein the printed conductive electrode is transparent.

Description

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

(1) Specific embodiments of the invention will further be described by way of example only.

(2) Embodiments of the present invention relate to a simple method of producing printable conductive ink comprising a dispersion of conductive material in a viscous liquid which does not necessarily contain a polymeric additive and, also, a method of using this ink for the production of a transparent and conductive electrode pattern. In certain examples of the printable conductive ink, the rheology of the viscous liquid may be controllable to allow it to be adapted for use with a variety of printing techniques.

(3) The absence of a polymeric additive in the conductive ink may result in the deposition of the conductive material only, a drawback of which may be low adhesion of the conductive material to the substrate, something which is provided by the polymeric additive component of typical conductive inks. The result of this, for example, may be poor robustness of the printed electrodes to any physical abrasion, hindering further over-printing or processing. One example of a technique that may be used to overcome this is the deposition of a uniform polymer coating onto the substrate before the deposition of the electrode. Deposition of a polymer on the substrate may increase the robustness of electrodes to a point where they can be processed further without easily damaging the deposited electrode and, also, without effecting the conductivity of the electrode. Addition of a polymer to the conductive ink prior to deposition may cause reduced conductivity as a result of decreased direct contact between neighbouring conductive particles brought about from the insulating layer of polymeric additive on the surface of each particle. Such insulation of the conductive materials may reduce the conductive contact between neighbouring particles and reducing the overall conductivity of the electrode.

(4) In one embodiment of the present invention, the viscous liquid used as a medium for the conductive material may be synthesized by combining equimolar quantities of a first composition comprising an amine and a second composition comprising a carboxylic acid. These compositions may be mixed in a round-bottom flask fitted with a reflux condenser. This process can be highly exothermic and, after mixing, the product can be allowed to cool to form a viscous liquid that is stable at room temperature. The viscous liquid may be stored for extended periods of time without any alteration to the rheological properties of the liquid.

(5) By way of example, the first composition may consist of one or more primary amines represented by formula 1, wherein, each of R.sup.1 and R.sup.2 is independently H or C.sub.1-5 with a total carbon count of less than 6, or a carbon-bridged diamine represented by formula 2, wherein R.sup.1 and R.sup.2 consists of H or C.sub.1-5. Also, the second composition may consist of one or more carboxylic acids represented by formula 3, wherein R consists of C.sub.1-5 or carbon-bridged dicarboxylic acids represented by formula 4, wherein R.sup.1 and R.sup.2 consist of H or C.sub.1-5.

(6) ##STR00001##

(7) An exemplary method of forming the printable conductive ink and printing a transparent electrode using the ink may involve adding 0.5 moles of sec-butylamine (36.57 grams) to a two-necked round-bottom flask fitted with a reflux condenser, which has been placed in a fume-cupboard. With stirring using a magnetic stirrer bar, 0.5 moles of acetic acid (30.03 grams) can be added slowly over the course of 10 minutes by injection through a suba-seal fitted to the second neck of the flask. The reaction may be stirred for 30 minutes or until the liquid has cooled to room temperature. Once the liquid has cooled it can be decanted into a sealable container and stored until required. To make the conductive ink, silver nanowires (108 nm30 m) coated with PVP may be added with stirring (250 rpm) using an overhead stirrer fitted with a paddle. Silver nanowires may be added to a concentration from 5 to 15 percent of the total weight of the mixture with stirring. Following addition of the silver nanowires, the mixture may be sonicated for 30 minutes using a sonic bath. The sonicated mixture may then be stirred for a further hour at 250 rpm to ensure good dispersion. The substrate on which the electrode is to be printed may be coated with a thin film of polyvinylpyrollidone (PVP). Once the conductive ink has been printed in the required pattern on the PVP coated substrate, the substrate may be heated in an oven fitted with an exhaust gas extractor at temperatures from 100 C. to 150 C. for from 1 to 15 minutes.

ALTERNATIVE EMBODIMENTS

(8) Alternative embodiments which may be apparent to the skilled person on reading the above description may nevertheless fall within the scope of the invention, as defined by the accompanying claims.