US-12624208-B2 - Low-shear viscosity reducing additive

US12624208B2US 12624208 B2US12624208 B2US 12624208B2US-12624208-B2

Abstract

A composition contains: (a) a first polyorganosiloxane; (b) 50-80 volume percent, based on composition volume, of conductive fillers; and (c) 0.1 to 2.0 weight-percent, based on composition weight, of a second polyorganosiloxane different from the first polyorganosiloxane, the second polyorganosiloxane having an average of 0.5 to 1.5 anhydride groups per molecule.

Inventors

Dan Zhao
Shane MANGOLD
Richard Cooper
Dongchan Ahn
Kyle McDonald
Joseph Sootsman
Darren Hansen

Assignees

DOW SILICONES CORPORATION
DOW GLOBAL TECHNOLOGIES LLC

Dates

Publication Date: 20260512
Application Date: 20220113

Claims (8)

1 . A composition comprising: a. a first polyorganosiloxane; b. 50-80 volume-percent, based on composition volume, of conductive fillers; and c. 0.1 to 2.0 weight-percent, based on composition weight, of a second polyorganosiloxane different from the first polyorganosiloxane, the second polyorganosiloxane having an average of 0.5 to 1.5 anhydride groups per molecule; wherein the second polyorganosiloxane has average chemical structure (II): R″R 2 SiO—(R 2 SiO) n —SiR 2 R″ (II) where “n” has an average value in a range of 40 to 200, R is independently in each occurrence selected from a group consisting of C 1 -C 8 hydrocarbyl groups, and R″ is independently in each occurrence selected from a group consisting of C 1 -C 8 hydrocarbyl groups, and anhydride groups; and where the first polyorganosiloxane has a lower dynamic viscosity than the second polyorganosiloxane.
2 . The composition of claim 1 , wherein the first polyorganosiloxane is free of anhydride groups.
3 . The composition of claim 2 , wherein the first polyorganosiloxane has average chemical structure (I): R′R 2 SiO—(R 2 SiO) m —SiR 2 R′ (I) where each R and R′ is independently in each occurrence selected from a group consisting of C 1 -C 8 hydrocarbyl groups and “m” is selected so that the first polyorganosiloxane has an average dynamic viscosity in a range of 0.04 to 55 Pascal*seconds.
4 . The composition of claim 3 , wherein each R′ is independently selected from vinyl and methyl groups.
5 . The composition of claim 1 , wherein the conductive filler is any one or any combination of more than one selected from a group consisting of alumina, zinc oxide, alumina trihydrate, boron nitride, aluminum nitride, silver flake, and silver coated particulates.
6 . The composition of claim 1 , where the anhydride groups have average chemical structure (III): where X is independently in each occurrence selected from hydrogen and C 1 -C 8 hydrocarbyl-containing groups and “a” is independently in each occurrence a value in a range of one to 6.
7 . The composition of claim 6 , wherein either X is independently in each occurrence selected from hydrogen and an aromatic group and “a” is 2, or X is hydrogen and “a” is 3.
8 . The composition of claim 6 , wherein X is independently in each occurrence an aromatic group.

Description

FIELD OF THE INVENTION The present invention relates to conductive compositions of conductive filler dispersed in a polyorganosiloxane matrix that includes low-shear viscosity reducing additive. INTRODUCTION Thermally and electrically conductive (jointly, “conductive”) composites are generally polyorganosiloxane matrix materials filled with conductive filler particles to enhance the conductivity through the matrix material. Conductive composites are useful for enhancing the conductivity between two components by serving as an interface material between the two components. In some applications it is desirable for conductive composites to have a relatively high low-shear viscosity in order to have positional stability—that is, to enhance the ability of the conductive composite to remain in a particular position and shape upon application. However, in other applications it is desirable for conductive compositions to have a low viscosity at low shear such as in self-leveling applications and those applications where the composition must be pressed to a particularly thin layer between components. Applications where the conductive composition is poured into a form or onto a substrate also benefit from a low low-shear viscosity so the conductive composition can flow over the form or substrate and fill pores, voids or gaps, and/or flow around objects such as wires. It is these latter conductive compositions that have a low viscosity at low shear that are the subject of the present invention. A technical challenge in conductive composites is in enhancing conductivity by increasing filler loading while achieving a low enough composite viscosity to meet application needs. Generally, increasing the concentration of conductive filler will increase the conductivity of the composite but will also increase the viscosity of the composite. In order to maximize the amount of conductive filler, it is desirable to find a way to reduce the low-shear viscosity of a conductive composite without reducing the concentration of conductive filler. Even more desirable is to identify such an additive that is a polysiloxane-based additive so that the additive is optimally compatible with the polyorganosiloxane matrix of the conductive composite. BRIEF SUMMARY OF THE INVENTION The present invention provides a polyorganosiloxane-based additive that lowers the low-shear viscosity of a conductive composite without reducing the concentration of conductive filler. The present invention is a result of discovering that a polyorganosiloxane additive with an average of 0.5 to 1.5 anhydride groups per polyorganosiloxane molecule can be added to a conductive composite at a concentration of 0.1 to 2.0 weight-percent, based on conductive composite weight, and reduce the low-shear viscosity of the conductive composite without reducing the filler loading. Surprisingly, the anhydride-functional polyorganosiloxane additive can have a higher dynamic viscosity than the polymer that serves as the primary matrix material of the composition to which the additive is added, yet the additive can still reduce the composition viscosity. In a first aspect, the present invention is a composition comprising: (a) a first polyorganosiloxane; (b) 50-80 volume percent, based on composition volume, of conductive fillers; and (c) 0.1 to 2.0 weight-percent, based on composition weight, of a second polyorganosiloxane different from the first polyorganosiloxane, the second polyorganosiloxane having an average of 0.5 to 1.5 anhydride groups per molecule. The present invention is useful as a conductive composite. DETAILED DESCRIPTION OF THE INVENTION Test methods refer to the most recent test method as of the priority date of this document when a date is not indicated with the test method number. References to test methods contain both a reference to the testing society and the test method number. The following test method abbreviations and identifiers apply herein: ASTM refers to ASTM International methods; EN refers to European Norm; DIN refers to Deutsches Institut für Normung; ISO refers to International Organization for Standards; and UL refers to Underwriters Laboratory. Products identified by their tradename refer to the compositions available under those tradenames on the priority date of this document. “Multiple” means two or more. “And/or” means “and, or as an alternative”. All ranges include endpoints unless otherwise indicated. “Hydrocarbyl” refers to a univalent group formed by removing a hydrogen atom from a hydrocarbon and includes alkyl and aryl groups. “Alkyl” refers to a hydrocarbon radical derivable from an alkane by removal of a hydrogen atom. An alkyl can be linear or branched. “Aryl” refers to a radical formable by removing a hydrogen atom from an aromatic hydrocarbon. “Low-Shear Viscosity” for a composition is determined according to the following oscillatory shear strain amplitude sweep (“Strain Sweep”) method. Provide a pair of 25 millimeter (mm) diameter