Xerox are continuing to add to their patent portfolio of silver nanoparticle inks for printed electronics. A new patent was granted on 4th Dec 2012 adding to the one already granted on 17th April 2012. These two patents are summarised below:
US8158032 (B2) – SILVER NANOPARTICLE INK COMPOSITION FOR HIGHLY CONDUCTIVE FEATURES WITH ENHANCED MECHANICAL PROPERTIES
Abstract: A conductive ink composition comprising organic-stabilized silver nanoparticles and a solvent, and a polyvinyl alcohol derivative resin of Formula (1) wherein R1 is a chemical bond or a divalent hydrocarbon linkage having from about 1 to about 20 carbons; R2 and R3 are independently an alkyl, an aromatic or substituted aromatic group having from about 1 to about 20 carbon atoms; x, y and z represent the proportion of the corresponding repeat units respectively expressed as a weight percent, wherein each repeat unit is randomly distributed along polymer chain, and the sum of x, y and z is about 100 weight percent, and wherein the polyvinyl alcohol derivative resin is present in an amount of from 0.1 to about 5 weight percent of the ink composition.
US8324294 (B2) – SOLVENT-BASED INKS COMPRISING SILVER NANOPARTICLES
Abstract: High performing nanoparticle compositions suitable for printing, such as by inkjet printing, are provided herein. In particular, there is provided a conductive ink formulation comprising silver nanoparticles which has optimal performance, such as, reduced coffee ring effect, improved adhesion to substrates, and extended printhead de-cap time or latency time. The ink formulation comprises two or more solvents and a resin.
The key technology improvements over the general prior art are for the development of inks which do not dry out and clog the printhead along with improvements in the adhesion of the ink to the substrate, reduction of the coffee ring effect and reduction of particle aggregation which leads to black dots in the printed lines.
The improved adhesion is as a result of the incorporation of a resin in the ink based on a polyvinyl alcohol derivative. The earlier patent goes into some detail over the formulae for these resins.
The extended drying times to prevent printhead clogging are the result of incorporation of two or more ink vehicles (solvents) with vapour pressure properties as described in the second patent. Typical compositions are based on aliphatic hydrocarbons comprising at least one cyclohexane ring, cyclic terpene, cyclic terpinene, terpineol, methyl naphthalene, and mixtures thereof. Typical drying times are in excess of 5 hours and one claim states up to about 1 week.
The nanoparticles are stabilised with organo-amines, the first patent gives more detail on these structures, a preferred compound is dodecylamine.
As always please leave a comment if you require further details or are interested in patent landscapes related to these conductive inks.