US-12624169-B2 - Filled silicone composition containing succinic anhydride functional siloxane thixotropic agents

Abstract

A composition contains filler particles dispersed in a matrix material, wherein the matrix material includes: (a) a first polyorganosiloxane that comprises an average of 2 or more succinic anhydride groups per molecule; and (b) a second polyorganosiloxane other than the first polyorganosiloxane; wherein the filler particles are present at a concentration in a range of 15 to 80 volume-percent based on composition volume and wherein the first polyorganosiloxane is present at a concentration sufficient to provide succinic anhydride groups at a concentration of 0.30 to 200 micromoles per gram of matrix material.

Inventors

• Zhanjie Li
• Kyle McDonald
• Andrés E. Becerra
• Joseph Sootsman
• Chi-Hao Chang
• Darren Hansen
• Dongchan Ahn
• Richard Cooper

Assignees

• DOW SILICONES CORPORATION
• DOW GLOBAL TECHNOLOGIES LLC

Dates

Publication Date

20260512

Application Date

20220113

Claims (9)

1. 1 . A composition comprising filler particles dispersed in a matrix material, wherein the matrix material comprises: a. a first polyorganosiloxane that comprises an average of 2 or more succinic anhydride groups per molecule; and b. a second polyorganosiloxane other than the first polyorganosiloxane; wherein the filler particles are present at a concentration in a range of 15 to 80 volume-percent based on composition volume and wherein the first polyorganosiloxane is present at a concentration sufficient to provide succinic anhydride groups at a concentration of 0.30 to 200 micromoles per gram of matrix material; wherein the first polyorganosiloxane has the following average chemical structure: where R′ is independently in each occurrence selected from a group of divalent hydrocarbons having from one to six carbon atoms, R is independently in each occurrence selected from a group of hydrocarbyls having from one to eight carbon atoms, and n is a value in a range of 5-150.
2. 2 . The composition of claim 1 , where each R′ is —CH 2 CH 2 CH 2 — and each R is methyl.
3. 3 . The composition of claim 1 , wherein the second polyorganosiloxane is a vinyl functional polyorganosiloxane.
4. 4 . The composition of claim 3 , wherein the matrix material further comprises a third polysiloxane comprising two or more silyl hydride groups.
5. 5 . The composition of claim 1 , wherein the filler particles comprise thermally conductive filler particles at a concentration in a range of 40 to 80 volume-percent based on composition volume.
6. 6 . The composition of claim 5 , wherein: i. when the thermally conductive filler is present at a concentration in a range of 40 to 70 volume-percent based on composition volume then the first polyorganosiloxane is present at a concentration sufficient to provide concentration of succinic anhydride groups in a range of 7.5 to 200 micromoles per gram of matrix material; and ii. when the thermally conductive filler is present at a concentration of greater than 70 and at the same time 80 or less volume-percent based on composition volume, then the first polyorganosiloxane is present at a concentration sufficient to provide a concentration of succinic anhydride groups in a range of 0.3 to 120 micromoles per gram of matrix material.
7. 7 . The composition of claim 5 , wherein the further comprises a filler treating agent.
8. 8 . The composition of claim 1 , wherein the filler particles comprise electrically conductive filler particles that are present at a concentration in a range of 15 to 60 volume-percent based on composition volume.
9. 9 . The composition of claim 8 , wherein the second polyorganosiloxane is a vinyl functional polyorganosiloxane and wherein the first polyorganosiloxane is present at a concentration sufficient to provide succinic anhydride groups at a concentration in a range of 7 to 160 micromoles per gram of vinyl functional polyorganosiloxane.

Description

FIELD OF THE INVENTION The present invention relates to filled silicone compositions that contain succinic anhydride terminated siloxane thixotropic agents. INTRODUCTION Filled silicone compositions comprise a filler dispersed in a matrix material that comprises a polysiloxane component. Filled silicone compositions are used in many applications including as conductive silicone compositions such as thermally conductive materials and electrically conductive materials. The filler in conductive silicone compositions helps increase the conductive character of the composition. Thermally conductive silicone compositions typically contain thermally conductive fillers and electrically conductive silicone compositions typically contain electrically conductive fillers. The fillers are often present at concentrations of 15 volume-percent (vol %) or more and can be present at concentrations up to 80 vol % based on filled silicone composition volume. Increasing the amount of conductive filler can increase the conductive characteristics of the silicone composition, but it also typically increases the filled silicone composition's viscosity, which can cause the silicone composition to be difficult to apply to substrates (low workability). As a result, there has been tension between maximizing conductive properties of a silicone composition versus maintaining workability of the silicone composition. It is desirable to have high workability by having low viscosity under shear, but it is also often desirable to have high viscosity under low or no shear to maintain the shape and location (that is, physical stability) where it is placed. Shear thinning compositions have a relatively high viscosity under little or no shear to provide composition stability while demonstrating relatively lower viscosity under shear to allow extrusion. As a result, shear thinning compositions can readily be applied by relatively high shear methods such as extrusion yet maintain physical stability once applied. There are ways to introduce shear thinning character to a filled silicone composition. However, the challenge is identifying how to induce shear thinning behavior in a filled silicone composition while still achieving a low enough viscosity under shear so as to allow for extrusion of the composition. Many methods for increasing shear thinning character often result in reduced extrusion/flow under shear. Shear thinning behavior is often characterized by a composition's “thixotropic index”, which is a ratio of the viscosity at a low shear condition divided by the viscosity at a high shear condition. Increasing the thixotropic index corresponds to increasing the shear thinning character of a composition. The thixotropic index can be increased by increasing the low shear viscosity, decreasing the high shear viscosity, or a combination of these. It can be desirable, however, to preferentially increase the low shear viscosity relative to decreasing high shear viscosity. Increasing low shear viscosity enhances physical stability and compositional stability (settling of the filler out from the composition) once applied or when in storage. When those features are of primary importance, such as in vertical applications where the composition should not drip or sag, it is desirable to increase low shear viscosity as much as possible. Changing high shear viscosity up or down can impact the method of deposition or extrusion of the composition in undesirable ways so it can be desirable to minimize the change in high shear viscosity. An objective of the present invention is to identify an additive for filled silicone compositions that preferentially increases the low shear viscosity of a filled silicone composition relative to its high shear viscosity in order to increase the thixotropic index of the filled silicone composition. More specifically, an object of the present invention is to identify an additive for filled silicone compositions comprising 15 to 80 vol % filler, based on filled silicone composition volume, that increases the thixotropic index of the composition while preferentially increasing the Maximum Viscosity relative to Minimum Viscosity of the composition and while achieving a Minimum Viscosity of 200 Pascal*seconds (Pa*s) or less as determined with a strain sweep method over a strain amplitude range of 0.01 percent (%) to 300% as described herein below. Even more desirable is if the additive can at the same time increase the thixotropic index of the filled silicone composition by 50% or more, preferably 75% or more, and most preferably 100% or more. BRIEF SUMMARY OF THE INVENTION The present invention provides a solution to the challenge of identifying an additive for filled silicone compositions that preferentially increases the low shear viscosity of a silicone composition relative to its high shear viscosity in order to increase the thixotropic index of the composition. The additive of the present invention serves as a thixotropic age