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.

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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

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:

ink1

Patterning after the ink deposition:

ink2

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:

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.

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.

Inorganic Nanoparticle Inks for Printed Electronics

Silicon ink has sometimes been described as a “Dream Material” for printed electronics.  Conductive or semi-conductive inks that can be printed directly onto a variety of substrates to create transistors or other electronic devices have been talked about and promoted for a number of years but few companies have succeeded in commercializing products for the mass market.  Silicon ink has been promoted as an enhancer for the production of solar cells to squeeze an extra few percent efficiency from the panel.  One Silicon-valley company NanoGram Corp. acquired last year by the Teijin Group has developed a silicon ink using a laser pyrolysis method to create stable nanoparticles in a dispersion that can be printed by various means including spin coating and inkjet processes.

A recent patent from NanoGram US8263423 was granted on 11 Sept 2012 and completes a trio of US patents granted for their silicon ink approach.  The other patents are US7993947 and US7892872.  These patents all claim a priority date of 3 Jan 2007 for the US provisional application first filed.  The text of all three patents is more or less the same but differs in the claims, each one covering a different aspect of the invention.  The basic technology is described in the first section “Field of the Invention”:

The invention relates to dispersions/inks of silica/germania particles, such as doped silica particles. The invention further relates to inks that are suitable for ink jet printing. Additionally, the invention relates to the use of doped silica/germania particles for the doping of semiconductor substrates, such as through the drive in of dopants with heat and/or light from a silica/germania deposit formed through inkjet printing onto the semiconductor surface.

The three patents break down the invention into i) the dispersion and method for making the dispersion; ii) the method for depositing the dispersion onto a substrate (inkjet printing); and iii) the method for forming solar cells and optical components.

The following paragraph from the text was selected to describe the dispersion approach:

The dispersions comprise a liquid and the dispersed silica particles, which may or may not be surface modified. In general, silica particles formed by laser pyrolysis can be well dispersed in water or alcohols at moderate concentrations with no surface modification, although higher concentration dispersions generally can be formed with surface modification. Suitable alcohols include, for example, small aliphatic alcohols, such as methanol, ethanol, propylene glycol, butanediol, mixtures thereof and the like. Upon surface modification, the silica particles can be dispersed in a broader range of solvents and solvent blends through the matching of the chemical properties of the surface modifying agent with the liquid. Thus, following surface modification, the particles can be well dispersed in a range of less polar solvents, such as ethyl lactate, n-methylpyrrolidinone, gamma-butyl lactone, and the like.

The following paragraph was selected to illustrate the printing approach:

While various coating and printing approaches are suitable, inkjet printing offers desirable features with respect to speed, resolution and versatility with respect to real time selection of deposition patterning while maintaining speed and resolution. However, practical deposition using inkjet printing with inorganic particles requires dispersion properties that have not been available prior to development of both the techniques to form high quality silica nanoparticle along with the improved ability to form high quality dispersions from these particles. Thus, the particles produced using laser pyrolysis combined with the improved surface modification approaches and dispersion techniques provides for the formation of inks that are amenable to inkjet deposition.

The following paragraphs were selected to describe the solar cell modifications:

To deliver dopant into the semiconductor from the silica deposit, the material is heated. For example, the structure can be placed into an oven or the like with the temperature set to soften the particles such that the dopants can diffuse into the substrate. The time and temperature can be adjusted to yield a desired dopant migration into the substrate…

Following the drive in of the dopant, it may or may not be desirable to remove the silica. For photovoltaic applications it is generally desirable to remove the silica to expose the doped semiconductor for the application of conductive electrical contacts. To remove the silica, the oxide can be etched, for example, using conventional approaches, such as using wet (chemical) etching or plasma etching.

Of course, you would need to review the claims to see exactly what has been allowed by the examiner and to understand the scope of the granted patent.

Phil’s Comments

It is quite common to see a provisional patent application emerge as several patents described as continuations of the first or earlier patent.  These can also appear as divisional patents and arise because the patent examiner or inventor has noted that the original application contains more than one invention.  These days the examiners are more strict in ensuring that the method and the material inventions are separated out.  In this case the distinction between the dispersion, the printing method and the application to solar cells or optical displays has been identified and separated into the three patents reviewed here.

I have not seen any recent evidence that the Teijin group have announced any products based on this approach and about 1 year has elapsed since they were actively promoting the technology.  It has been a tough year for solar cell manufacturers and a number of promising companies exploring plastic electronics approaches have filed for bankruptcy (e.g. Konarka and Novasolar).  It remains to be seen whether the silicon ink approach will be adopted as a means to increase efficiency and lower cost of conventional solar cells.