I recently spotted a patent for copper based metallic inks jointly granted to Applied Nanotech Holdings, Inc. and Ishihara Chemical Co., Ltd. The conductive inks I have previously reported on have been silver or graphene based, these can be very expensive and so there is always interest in a lower cost alternative. Copper metal is a standard in the electronics industry and is about one tenth the cost of silver.
Patent summary:
US8404160 – METALLIC INK
Inventor(s): LI YUNJUN [US]; ROUNDHILL DAVID MAX [US]; LI XUEPING [US]; LAXTON PETER B [US]; ARIMURA HIDETOSHI [US]; YANIV ZVI [US]
Applicant(s): APPLIED NANOTECH HOLDINGS INC [US]; ISHIHARA CHEMICAL CO LTD [JP]
Filing date: 31/03/2009
Issue date: 26/03/2013
Abstract
A metallic ink including a vehicle, a multiplicity of copper nanoparticles, and an alcohol. The conductive metallic ink may be deposited on a substrate by methods including inkjet printing and draw-down printing. The ink may be pre-cured and cured to form a conductor on the substrate.
Claim 1:
1. A conductive metal ink comprising: a vehicle comprising two or more oxygenated organic compounds; copper nanoparticles; and a medium length chain aliphatic alcohol, wherein the ink does not comprise a binder.
There are a further 23 claims giving more details of the components mentioned in claim 1.
Two figures from the patent give a flow chart for two processes which can be used:
Direct printing:
Patterning after the ink deposition:
Phil’s Comments
This is a key patent for copper inks and has a broad first claim which had to be modified from the original application by the addition of the restriction that the ink does not contain a binder and I suspect this was to get around some of the prior art identified by the patent examiner.
Six very detailed examples are given which illustrate the invention and provide further details of the printing process, the curing or sintering that is applied to produce the conductive tracks on a range of materials including flexible substrates.
Phil's Patent Picks 
A further patent in this series has been granted: US8506849. There are two claims and they are quite specific to copper ink formulations:
1. A conductive ink comprising: about 15 wt % to about 65 wt % copper nanoparticles; a vehicle comprising: about 10 wt % to about 50 wt % water; about 40 wt % to about 60 wt % cyclohexanol; and an amount of isopropanol such that a ratio of water to isopropanol is between about 1:1 and about 1:2; and a dispersant.
2. A conductive ink comprising: about 15 wt % to about 65 wt % copper nanoparticles; a vehicle comprising: about 1.0 wt % to about 30 wt % water; about 20 wt % to about 80 wt % isobutanol; and an amount of isopropanol such that a ratio of water to isopropanol is between about 1:1 and about 1:2; and a dispersant.
The patent can be viewed here: http://worldwide.espacenet.com/publicationDetails/originalDocument?FT=D&date=20130813&DB=worldwide.espacenet.com&locale=en_EP&CC=US&NR=8506849B2&KC=B2&ND=4