Method for producing heterogeneous composites

Abstract

A method for selecting materials and processing conditions to prepare a heterogeneous structure in situ via the reaction of a homogeneous mixture of a reactive organic compound and a filler, which may then optionally be sintered. The method is employed to provide a heterogeneous composite possessing exceptionally high thermal and / or electrically conductivities for a given concentration of conductive filler. The choice of materials as well as processing conditions employed, as will be described below, have a strong effect on the rate domain formation / heterogeneity of the structure formed, the extent of filler particle-particle interactions within filler-rich domains, and ultimately the thermal and / or electrical conductivity. Proper choice of these conditions can lead to composites having enhanced properties at a reduced bulk filler concentration.

Description

CROSS REFERENCE[0001]This application claims the benefit of, and incorporates by reference, U.S. Provisional Patent Application No. 60 / 896,961 filed on Mar. 26, 2007 with the United States Patent and Trademark Office.FIELD OF THE INVENTION[0002]The present invention relates to a method for creating heterogeneous polymer-filler composites in situ via a reaction of a homogeneous mixture of a filler and a reactive organic compound. The heterogeneous structure comprises highly filler-rich areas whose concentration is greater than that of the bulk filler concentration.BACKGROUND OF THE INVENTION[0003]Electrically conductive polymer composites often consist of electrically insulating polymers filled with electrically conductive fillers. Such fillers often consist of metal- or carbon-based fillers often in the form of flake or fibers. In order to make the composite conductive, the fillers are added to the point a critical filler concentration is reached at which the composite changes from ...

AI Technical Summary

Benefits of technology

"The present invention provides a method for producing a heterogeneous structure in a composite by reacting a reactive organic compound with a filler. The method allows for the formation of a heterogeneous structure with exceptional thermal and electrical conductivities for a given concentration of filler. The choice of materials and processing conditions can affect the rate domain formation and the interaction between filler particles, resulting in enhanced properties at a reduced bulk filler concentration. The method can lead to electrically percolation threshold concentrations of the filler, enabling the formation of a fused network of filler particles. The filler can be thermally or metal sinterable, and the resulting composite has improved thermal and electrical conductivities. The method can be performed with a solvent-free composition and can lead to enhanced properties at a reduced filler concentration."

Problems solved by technology

In many instances the level of filler required leads to undesirable sacrifices in other important physical characteristics of the composite, such as dispense viscosity, adhesion, impact strength, among other things.

In some instances, the cost of the filler is a limiting factor, particular for such fillers as gold, silver, or carbon fibers.

In many instances, undesirable increases in viscosity occur to the point handling (or dispensing) becomes an issue which often limits the thermal conductivity that can be achieved.

However, a downside to this approach, as seen in epoxy based formulations, is these low molecular weight species cause shrinkage issues, void formation, and delamination when the adhesive is cured.

While highly thermally conductive, this material is quite limited in its ability to adhere to surfaces and has an intrinsically high modulus owing to pure filler remaining once the solvent is removed.

Moreover, most packaging processes prefer low solver to solvent-less materials owing to the complexities and environment concerns with removing solvent.

Unfortunately, sintering in not achieved at low to moderate fillers loadings.

This limitation is associated with the lack of direct filler particle contacts required for filler to occur due to the matrix material that coats them.

It is only at very high volume percent filler that some sintering occurs, but at such concentrations the unreacted adhesive composition becomes extremely viscous and even solid-like and lacks the desirable polymeric attributes such as good adhesion, toughness, etc.

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