Conductive Silicone Composition With Thixotropic Viscosity Control
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Solution Overview
Problem
Existing filled silicone compositions face a challenge in achieving high workability with low viscosity under shear for easy application while maintaining high viscosity under low or no shear for physical stability, particularly when filled with conductive fillers above 15 volume-percent, which often results in reduced extrusion and flow.
Innovation Solution
Incorporating carboxylic acid-functional linear polyorganosiloxanes as thixotropic agents in the silicone compositions, which preferentially increase low shear viscosity relative to high shear viscosity, thereby enhancing the thixotropic index and maintaining a Minimum Viscosity of 200 Pascal*seconds or less.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the amount of conductive filler is increased to maximize conductive properties, then the conductive characteristics of the silicone composition are improved, but the viscosity increases making the composition difficult to apply
Solution Approach 1:
The patent changes the chemical parameters of the silicone matrix by introducing carboxylic acid-functional polyorganosiloxane thixotropic agents. This modifies the viscosity characteristics of the system, enabling high filler loading (15-80 vol%) while maintaining workability through shear thinning behavior. The thixotropic index is specifically adjusted to balance low shear viscosity (for stability) and high shear viscosity (for extrusion).
Solution Approach 2:
The patent creates a composite system combining conductive filler particles with a thixotropic silicone matrix containing carboxylic acid-functional polyorganosiloxane. This composite structure allows the filler to provide conductive properties while the thixotropic matrix provides shear-dependent viscosity control, resolving the contradiction between filler loading and workability.
2Stability of the object's composition
If low shear viscosity is increased to enhance physical stability and prevent settling, then composition stability is improved, but extrusion and flow under shear are reduced
Solution Approach 1:
The patent introduces dynamic, shear-dependent viscosity characteristics through thixotropic agents. The viscosity is not fixed but changes dynamically based on applied shear stress: high at low shear for stability, low at high shear for extrusion. This dynamic behavior is quantified by the thixotropic index (ratio of low shear to high shear viscosity).
Solution Approach 2:
The patent specifically adjusts the thixotropic index parameter by incorporating carboxylic acid-functional polyorganosiloxane at controlled concentrations (0.01-5 wt%). This parameter optimization enables simultaneous achievement of high low-shear viscosity (for stability) and adequate high-shear flow (for extrusion), resolving the stability-extrusion contradiction.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The addition of carboxylic acid-functional polyorganosiloxanes significantly increases the thixotropic index by 50% or more, ensuring stable composition application and physical stability without significantly affecting high shear viscosity, allowing for effective extrusion and deposition.
Implementation Method 1
carboxylic acid-functional linear polyorganosiloxanes as thixotropic agents in the silicone compositions, which preferentially increase low shear viscosity relative to high shear viscosity, thereby enhancing the thixotropic index
Data Source
AI summary
A composition contains filler particles dispersed in a matrix material, wherein the matrix material contains: (a) 0.01 to 1.50 weight-percent of a first polyorganosiloxane, wherein first polyorganosiloxane is a linear polyorganosiloxane with an average of 2 or more carboxylic acid groups per molecule; and (b) 5 to 30 weight-percent of a second polyorganosiloxane that is free of carboxylic acid groups, wherein the second polyorganosiloxane is a liquid at 25 degrees Celsius and 101 megaPascals pressure; wherein the filler particles are present at a concentration in a range of 15 to less than 78 volume-percent based on composition volume and weight-percent values are relative to weight of the composition and wherein the composition is free of at least one of aliphatic diols and silicone polyethers.