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Synthesis of Metallic Nanoparticle Dispersions

a technology of nanoparticles and dispersions, applied in the field of nanoparticles, can solve the problems of limiting the processing of flake-based inks, unable to achieve conductivities of only 2 to 10% of bulk metal conductivity, and the current method of printing conductive compositions onto substrates has certain limitations

Inactive Publication Date: 2007-06-28
PCHEM ASSOC
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

"The present invention provides a composition of metallic nanoparticles dispersed in an aqueous medium that can be deposited on a substrate and form a cohesive conductive structure with good adhesion and conductivity under moderate temperature conditions. The composition has a resistivity in the range of 2 to 15 times the bulk resistivity of the corresponding metal. The invention also provides methods for synthesizing the metallic nanoparticle dispersion and forming a conductive structure on a substrate."

Problems solved by technology

Present methods of printing conductive compositions onto substrates have certain limitations.
These flake-based inks, however, generally cannot be processed at temperatures lower than 120° C. or at times less than 1 minute, regardless of temperature.
Furthermore, these materials are only capable of achieving conductivities of only 2 to 10% of bulk metal conductivity because of the continuous polymeric matrix and the manner with which the flakes pack together.
Conductivities as high as 20% of the bulk metal are possible when using such additives, but high temperatures are needed to decompose the metallo-organic into a conductive structure, and these high temperatures accordingly limit the range substrates suitable for use in conjunction with such ink systems.
Certain conductive ink compositions spread out on a substrate surface before curing, thus adversely impacting the ability to form structures of a certain, defined shape.
In addition, certain compositions incorporate organic solvents, which are difficult to dispose of.
Furthermore, systems comprising metallic nanoparticles dispersed in an organic solvent medium suffer from poor sintering characteristics once deposited onto a substrate, and may require comparatively long exposure to comparatively high temperatures in order to form conductive traces after deposition.
One potential hindrance to metallic nanoparticles' use in conductive inks is their limited ability to form relatively thick conductive traces.
While large metallic particles—typically characterized as having diameters of greater than about 500 nm—are limited in application because they do not sinter at low temperatures, large particles are nonetheless capable of forming thicker metal traces than metallic nanoparticles are capable of forming.
Hence, because of large metallic particles' inability to sinter and form conductive structures at low temperatures, manufacturers are limited in their ability to form thick conductive structures on substrates that are incapable of withstanding the temperatures necessary for large particles to cohere into conductive structures.
Furthermore, the difficulty in inducing large metallic particles to form conductive structures under moderate processing conditions also gives rise to a need for a method for forming thick conductive structures on substrates capable of tolerating only low temperatures.

Method used

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  • Synthesis of Metallic Nanoparticle Dispersions
  • Synthesis of Metallic Nanoparticle Dispersions
  • Synthesis of Metallic Nanoparticle Dispersions

Examples

Experimental program
Comparison scheme
Effect test

example 1

[0092] An initial solution was prepared by adding 7.5 grams of ammonium hydroxide (30% ammonia by weight) to 275 grams of water; 13.5 grams of heptanoic acid was added to this solution followed by 20.9 grams of 50% hydrazine hydrate aqueous solution. The ammonium hydroxide is necessary to allow the acid to dissolve in the water. Separately, 36 grams of silver nitrate was dissolved in 175 grams of water. The silver nitrate solution was added to the initial solution while stirring under nitrogen. The resultant product was flocculated and allowed to settle. Excess water was decanted off. The concentrated product was spread onto 5 mil polyester film with a 0.5 mil wire wound rod and then cured at 80° C. and 100° C. for 1-2 minutes resulting in cohesive and conductive silver films.

example 2

[0093] An initial solution was prepared by adding 2.1 grams of ammonium hydroxide (30% ammonia by weight) to 50 grams of water; 7.8 grams of heptanoic acid was added to this solution followed by 3 grams of 50% hydrazine hydrate aqueous solution. Separately, 10 grams of silver nitrate was dissolved in 50 grams of water. The silver nitrate solution was added to the initial solution while stirring under nitrogen. The resultant product was allowed to settle and the excess water decanted off.

[0094] The concentrated product was spread onto 5 mil polyester film with a 0.5 mil wire wound rod and then cured at 80° C. and 100° C. for 1-2 minutes resulting in cohesive and conductive silver films. The weight resistivity of a sample cured at 100° C. for 1 minute was measured to be 0.39 gram-ohms / m2 (˜2×bulk silver).

example 3

[0095] An ink composition was prepared by adding 50 grams of spherical silver powder (1-2 um mean diameter) to 50 grams of 35 wt % nanoparticle dispersion of Example 1 also containing 3 wt % of an acrylic copolymer latex (55 wt % polymer), 2 wt % of polyvinyl alcohol (25 wt % in water, Mw of 8,000-9,000), and 1 wt % ethylene glycol. The materials were mixed well together, and were milled in a mortar and pestle until a homogeneous mixture was obtained. A film of the resulting ink was deposited onto 0.005″ thick untreated polyester film with a 0.0015″ Bird film applicator. The wet film was cured in a 100° C. for 30 seconds followed by 60 seconds at 140° C. The weight resistivity of the resulting silver films was measured to be 1.3 gram-ohms / m2, approximately 8 times the resistivity of bulk silver. The adhesion of the film to the substrate was tested by applying a 4″ long strip of Scotch brand tape (3M Corporation) to the film, insuring good adhesion to the film by applying pressure wi...

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Abstract

Disclosed are compositions comprising metallic nanoparticles suitable for use in cohesive, highly conductive structures on substrates. Also disclosed are methods for synthesizing the compositions and methods for forming cohesive, highly conductive structures from the compositions.

Description

CROSS REFERENCE TO RELATED APPLICATIONS [0001] This application claims the benefit of U.S. Provisional Pat. App. No. 60 / 752,143, “Low Temperature Curing Inks Utilizing Metallic Nanoparticles As A Sintering Aid”, filed Dec. 20, 2005, U.S. Provisional Pat. App. No. 60 / 752,144, “Low Temperature Curing Inks Containing Metallic Nanoparticle Dispersions”, filed Dec. 20, 2005, and U.S. Provisional Pat. App. No. 60 / 752,628, “Capacitance Coupled Interactive Electronics Using Printed Conductors”, filed Dec. 21, 2005. The entirety of each of these applications is incorporated by reference herein in their entirety.FIELD OF THE INVENTION [0002] The present invention pertains to the field of nanoparticles. The present invention also pertains to the fields of conductive inks and of printable conductive features. BACKGROUND OF THE INVENTION [0003] Various scientific and patent publications are referred to herein. Each is incorporated by reference in its entirety. [0004] Thin, conductive metal films...

Claims

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Application Information

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Patent Type & Authority Applications(United States)
IPC IPC(8): C22C5/00B22F1/0545B22F1/102
CPCB22F1/0022B22F1/0062B22F9/24B22F2998/00B82Y30/00C09D11/52B22F1/0545B22F1/102
Inventor JABLONSKI, GREGORY A.MASTROPIETRO, MICHAEL A.WARGO, CHRISTOPHER J.
Owner PCHEM ASSOC
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