Aqueous Conductive Silver Ink

Printed electronics is continuing to grow as more and more applications are developed and commercialised.  One of the key stumbling blocks continues to be the practicalities of printing narrow conductive tracks and the ease of use of the materials and processes involved.  One of the key system components, often taken for granted,  is the ink.  The majority of conductive ink compositions in use today are solvent-based thick film systems designed for low speed screen printing.  Water based conductive inks and coatings offer significant ecological advantages over solvent-based compositions, as the latter release solvents into the atmosphere on drying.  Aqueous conductive inks, however, have so far not offered the high conductivity, or low electrical resistivity, achievable with solvent-based formulas.

Sun Chemical Corp. have just been granted a patent for an aqueous ink with high conductivity and good printing properties.  This invention more specifically relates to an aqueous conductive silver ink suitable for use in RFID and other electronic technologies. The composition is highly conductive and requires reduced drying energy. In addition, it may be applied to low cost substrates via high speed printing processes. The key components of the ink formulation include: (meth)acrylic copolymer or salt thereof; conductive particles; an anionic surface wetting agent; defoamer and water.  The first claim suggests the ink can be up to 80% water depending on the amount of the other ingredients.

The patent is US8709288 and it was issued on 29 April 2014.  The Inventors are Jason Rouse and Dave Klein.

The independent claims from the patent are listed below:

1. A method of forming a conductive pattern on a substrate comprising applying a conductive composition comprising (a) metallic silver conductive particles, (b) water soluble styrene/(meth)acrylic copolymer, (c) an anionic wetting agent, (d) defoamer and (e) 10 to 80% water, the composition providing a sheet resistance of less than 0.83 ohms/sq, on the substrate and drying the composition.
34. A method of forming a conductive pattern on a substrate comprising applying a conductive composition consisting essentially of (a) metallic silver conductive particles, (b) water soluble styrene/(meth)acrylic copolymer, (c) an anionic surfactant, (d) defoamer and (e) 10 to 80% water, the composition providing a sheet resistance of less than 0.83 ohms/sq, on the substrate and drying the composition.
37. A method of forming a conductive pattern on a substrate comprising applying a conductive composition consisting of (a) metallic conductive particles, (b) water soluble styrene/(meth)acrylic copolymer, (c) an anionic surfactant, (d) defoamer, (e) 10 to 80% water, and optionally another solvent, the composition providing a sheet resistance of less than 0.83 ohms/sq, on the substrate and drying the composition.

The differences above are subtle but important, claim 34 describes the composition with an anionic surfactant rather than a wetting agent, and claim 37 describes a more general formulation with any metallic conductive particle and optionally includes another solvent.  Each claim includes the requirement that the composition provides a resistance of less that 0.83 ohms/sq on the substrate.


Phil’s Comments:

Good to see that research into inks suitable for printed electronics is providing environmentally acceptable formulations.  Reducing solvents and also reducing the energy requirements for drying are all good directions for the ink design.  We sometimes forget the huge demand put upon the inks we use, for example they need good abrasion and chemical resistance when dried so that they are not easily scratched or wiped off during subsequent uses, they need to have proper rheology and substrate wetting properties to obtain good ink transfer and graphic reproduction. Additionally, the ink should possess good flexibility and thermal stability to withstand the physical deformation to which the substrate may be subjected.  Let’s remember the research that goes into the inks when we next see a printed electronics design in use!



Metal Nanoparticle Conductive inks Patented by Aculon Inc

Aculon Inc. were granted a patent on 15 October for “Electroconductive Inks made with Metallic Nanoparticles”.  Aculon are well known for their surface coatings using nanoparticle technology, featuring improved adhesion to a wide range of surfaces and adding functionality for numerous applications including printed electronics.  It is therefore no surprise that conductive inks are described with advantageous adhesion to a variety of substrates including silicon, glass and plastic.

The granted patent is US8558117 and the claims are quite broad but require the inks to have an omega substituted organophosphoric acid, this is the added ingredient which helps to improve the adhesion.

The first 10 claims are shown below:

What is claimed is: 1. An electroconductive ink comprising: (a) a dispersion of metal nanoparticles with a dispersant on the surface of the metal nanoparticles and as a separate component, (b) an omega substituted organophosphorus acid; the metal nanoparticles being present in amounts of 5 to 80 percent by weight and the omega substituted organophosphorus acid being present in amounts of 0.0005 to 5 percent by weight; the percentages by weight being based on total weight of the electroconductive ink.

2. The composition of claim 1 in which the metal is selected from copper, silver, palladium, gold or any combination thereof.

3. The composition of claim 2 in which the metal is silver.

4. The composition of claim 3 in which the dispersant is an organic carboxylic acid.

5. The composition of claim 4 in which the organocarboxylic acid contains from 4 to 36 carbon atoms.

6. The composition of claim 1 in which the metal nanoparticles have a particle size of 1 to 500 nanometers.

7. The composition of claim 1 in which the dispersion contains an organic diluent.

8. The composition of claim 7 in which the organic diluent is selected from hydrocarbons, alcohols, esters and ketones.

9. The composition of claim 1 in which the organo groups of the organophosphorus acid have omega substituted functional groups.

10. The composition of claim 1 in which the omega substituted functional groups are selected from phosphonic acid, carboxylic acid, hydroxyl, thiol and amine including various combinations thereof.

Phil’s Comments:

I have reported on a number of conductive ink patents over the past year or two and a common theme running through them is the need for good adhesion along with their conductivity.  The patents generally differ in the description of the adhesion promoting substances used in the nanoparticle inks and on other improved properties that enhance their application for printed electronics.  Successful conductive ink formulations are essential for printed electronics to become a mainstream technology for building new devices and specialist inks with patented formulations will continue to dominate the scene for a number of years before generic formulations will be cheaply available as we see for conventional inkjet printing.

Copper Inks for Printed Electronics

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



Filing date: 31/03/2009
Issue date: 26/03/2013

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.


Silver Nanoparticle Inks for Printed Electronics

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:


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.


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.

Phil’s Comments

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.


Printed Electronics Patents Granted in 2011 – Kovio Inc

This is the third in the series covering patents granted during 2011 in the printed electronics field.

US7977240: Metal Inks For Improved Contact Resistance

Joerg Rockenberger, Yu Chen, Fabio Zürcher, Scott Haubrich

Kovio, Inc.

Filing date: 13 Feb 2009; Issue date: 12 Jul 2011


Metal ink compositions, methods of forming such compositions, and methods of forming conductive layers are disclosed. The ink composition includes a bulk metal, a transition metal source, and an organic solvent. The transition metal source may be a transition metal capable of forming a silicide, in an amount providing from 0.01 to 50 wt. % of the transition metal relative to the bulk metal. Conductive structures may be made using such ink compositions by forming a silicon-containing layer on a substrate, printing a metal ink composition on the silicon-containing layer, and curing the composition. The metal inks of the present invention have high conductivity and form low resistivity contacts with silicon, and reduce the number of inks and printing steps needed to fabricate integrated circuits.

Phil’s Comments:

Kovio Inc. is one of the leading companies involved in printed electronics devices and have made significant progress in printing complex electronic devices such as RFID’s in which not only the antenna but also the associated electronics is printed by a solution deposition process.

Here is an extract from the patent which explains the problem faced in any printing method for electronic devices:

In integrated circuits, the devices (e.g., TFT, capacitors, diodes, etc.) are generally connected to each other with metal lines (i.e., interconnects). Integrated circuits with good performance generally include interconnects with low resistivity, and thus not all metals are suitable for use as interconnects. Typical examples of suitable metals are Al, Cu, Au and Ag. Often, metals used for interconnects in integrated circuits do not form low resistivity contacts with the device electrodes (e.g., gate and source/drain electrodes), which are usually made with n+ and/or p+ doped silicon. Therefore, in order to fabricate integrated circuits with good performance, a contact layer formed between the n+/p+ silicon and the metal lines often provides relatively low resistivity between the devices and the interconnects. Typically, silicides are the preferred contact layers used in microelectronic devices, because they can provide ohmic contacts to heavily doped semiconductors (e.g. n+/p+ silicon and/or germanium).

This patent describes metal ink compositions that have high conductivity and low contact resistance and can therefore reduce the number of inks and printing steps required to manufacture a device.  The patent also describes a method which comprises (a) forming a layer comprising silicon and/or germanium on a substrate, (b) depositing (e.g., by printing) a metal ink composition on the silicon-containing layer, and (c) curing the metal composition. In general, the metal ink compositions comprise a bulk metal and a silicide-forming transition metal source.

More details are available in the full patent specification which can be found here.  Email me or leave a comment if you would like any further details.


Printed Electronics Patents Granted in 2011 – Conductive Ink

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.