This is the second in the series covering patents granted during 2011 in the printed electronics field.
US7968011: Conductive Ink
Inventor(s): Gerardus Cornelis Overbeek, Michael Arnoldus Jacobus Schellekens, Alfred Jean Paul Bückmann
Assignee(s): DSM IP Assets B.V.
Filed: 6 Mar 2007; Issued: 28 Jun 2011
Abstract: A conductive ink comprising 10 to 75 wt % of at least one solvent comprising ≦20 wt % water; 0 to 50 wt % of at least one radiation curable material having a Mn in the range of from 50 to 10,000 g/mol; 5 to 70 wt % of at least one polyurethane having a Mw in the range of from 4,000 to 70,000 g/mol, 0 to 5 wt % of isocyanate-reactive component(s) bearing ionic or potentially ionic water-dispersing groups and a free isocyanate group content <0.5 wt % and 20 to 85 wt % of a conductive material.
The claims provide more details around the various components but rather than copying the claims I’ll explain in simple English.
The problem being solved by this invention is the lack of a common binder that can be used across a range of different conductive ink materials. The inventors have provided a polyurethane based binder which they have found can be used to create inks suitable for flexography, gravure and ink-jet printing. The method does not require high temperature curing and leads to good conductivity. Claim 1 requires that a UV radiation curing material is also included with the binder and this gives additional improvements in film properties and faster printing speeds.
The conductive materials are described as any form of conductive particle and the scope is very broad, including nanoparticles of silver or copper. The particles can be flakes, fibres, nanotubes or mixtures, the particles can be silver coated.
The system requires a solvent which can be alcohol based (e.g. ethanol, iso-propanol, etc.) or any from a broad range of esters, ethers, ketones, etc. and preferably contains less than 10% water.
Any reader interested in the full formulation should refer to the patent for details of the preferred formulations.