Molecular inks
A flake-less molecular ink suitable for printing (e.g. screen printing) conductive traces on a substrate has 30-60 wt % of a C 8 -C 12 silver carboxylate and 0.1-10 wt % of a polymeric binder, or 5-75 wt % of bis(2-ethyl-1-hexylamine) copper (II) formate, bis(octylamine) copper (II) formate or tris(octylamine) copper (II) formate and 0.25-10 wt % of a polymeric binder, and balance of at least one organic solvent, wherein the binder has ethyl cellulose, and the ethyl cellulose has an average weight molecular weight in a range of 60,000-95,000 g/mol and a bimodal molecular weight distribution.
1. A molecular ink comprising a flake-less printable composition of:
5-75 wt % of bis(2-ethyl-1-hexylamine) copper (II) formate;
0.25-10 wt % of a polymeric binder; and,
balance of at least one organic solvent,
all weights based on total weight of the composition,
wherein the binder comprises ethyl cellulose, and the ethyl cellulose has a weight average weight molecular weight in a range of 60,000-95,000 g/mol and a bimodal molecular weight distribution.
2. The ink according to claim 1 , wherein the bis(2-ethyl-1-hexylamine) copper (II) formate is present in an amount of 65-75 wt % and the composition comprises 0.5-2 wt % of the binder.
3. The ink according to claim 1 , wherein the composition comprises 2.5-5 wt % of the binder.
4. The ink according to claim 1 , wherein the binder further comprises one or more other polymers different from ethyl cellulose.
5. The ink according to claim 1 , wherein heating the ink to 125-250° C. on a substrate, under and inert or reducing atmosphere, results in the production of interconnected copper nanoparticles bound by the binder.
6. The ink according to claim 1 , wherein the ethyl cellulose comprises a mixture of ethyl celluloses, the mixture comprising a first ethyl cellulose having a weight average molecular weight in a range of from 60,000-70,000 g/mol and a second ethyl cellulose having a weight average molecular weight in a range of from 90,000-100,000 g/mol.
7. The ink according to claim 1 , wherein the solvent comprises an aromatic organic solvent.
8. The ink according to claim 7 , wherein the aromatic organic solvent comprises toluene, xylene, anisole, diethylbenzene or any mixture thereof.
9. The ink according to claim 7 , wherein the aromatic organic solvent comprises anisole.
10. A printed substrate comprising a conductive trace produced by a process comprising printing the ink as defined in claim 1 onto a substrate to form a trace of the ink on the substrate, and sintering the trace of the ink on the printed substrate to form the conductive metal trace.
11. The substrate according to claim 10 , wherein the printing is screen printing.
12. The substrate according to claim 11 which is flexible.
13. The substrate according to claim 12 , wherein:
the conductive trace has a sheet resistance of 5 mOhm/sq/mil or less;
the conductive trace does not develop an open circuit break over a period of at least 1 day;
the conductive trace can maintain said resistance with a change of 10% or less after 10 compressive bend or 10 tensile bend cycles according to ASTM Test F1683-02;
the conductive trace can maintain said resistance with a change of 10% or less after 1 compressive or 1 tensile crease cycle according to ASTM Test F1683-02; or,
an adhesive has a bond strength to the conductive trace of 4 lbs or greater without encapsulation according to IPC Shear Force Testing.