Thermally Conductive Polysiloxane Composition for Filler Stability
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Solution Overview
Problem
Thermally conductive polysiloxane compositions face challenges in balancing viscosity to prevent filler settling while maintaining application ease, especially in 2-part curable compositions, where high filler concentrations hinder effective shear thinning behavior.
Innovation Solution
Incorporating trialkoxy functional polysiloxanes with specific molecular weight and concentration to induce a preferential increase in low shear viscosity, achieving a thixotropic index of at least 50% higher than without the additive, suitable for both parts of a 2-part curable composition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the viscosity of the composition is increased to stabilize filler from settling, then filler stability is improved, but it becomes difficult to extrude during application onto a substrate
Solution Approach 1:
The composition exhibits shear-thinning behavior where viscosity dynamically changes based on applied shear rate. At low shear rates (storage), viscosity is high to prevent filler settling. At high shear rates (application), viscosity decreases to enable easy extrusion and spreading. This dynamic viscosity adjustment resolves the contradiction between filler stability and application ease.
Solution Approach 2:
The thixotropic agents modify the viscosity parameter of the composition in a shear-rate-dependent manner. The composition maintains high viscosity at rest for filler stability, but transitions to low viscosity under shear stress during application, allowing both requirements to be satisfied through parameter transformation.
2Ease of operation
If thixotropic agents are added to induce shear thinning behavior, then application ease is improved, but the high concentration of thermally conductive fillers creates an environment where solid filler-filler interactions effect viscosity and possible adsorption of thixotropic agents on to the filler surfaces may render the agent less effective
Solution Approach 1:
The polysiloxane matrix acts as an intermediary between the thixotropic agents and filler particles. The matrix provides a compatible medium that allows thixotropic agents to function effectively despite the presence of high filler concentrations, preventing direct adsorption of agents onto filler surfaces and maintaining their shear-thinning functionality.
Solution Approach 2:
The composition is designed as a composite system where thixotropic agents, polysiloxane matrix, and thermally conductive fillers work together synergistically. The specific combination and interaction of these components create a stable dispersion where thixotropic agents remain effective despite the challenging high-filler environment.
3Stability of the object's composition
If each part of a 2-part curable thermally conductive polysiloxane composition is made shear thinning with the same thixotropic agent, then filler stability in each part is improved, but ensuring compatibility and consistent performance when mixed becomes more complex
Solution Approach 1:
Both parts of the 2-part composition use the same thixotropic agent at the same concentration, ensuring homogeneous shear-thinning behavior. This homogeneity in additive selection and concentration simplifies compatibility assessment and ensures consistent performance after mixing, while maintaining filler stability in each separate part.
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 solution stabilizes filler in both parts of the composition, ensuring stable mixing and application while maintaining low viscosity under high shear, enhancing the thixotropic properties and preventing settling.
Implementation Method 1
Incorporating trialkoxy functional polysiloxanes with specific molecular weight and concentration to induce a preferential increase in low shear viscosity, achieving a thixotropic index of at least 50% higher than without the additive
Implementation Method 2
The solution stabilizes filler in both parts of the composition, ensuring stable mixing and application while maintaining low viscosity under high shear, enhancing the thixotropic properties
Implementation Method 3
Curable thermally conductive polysiloxane compositions are curable, meaning that they can react to form a crosslinked polysiloxane matrix comprising thermally conductive filler
Implementation Method 4
curable thermally conductive polysiloxane compositions are useful in the electronics industry to provide a thermal bridge between components such as a heat source and a heat sink
Data Source
AI summary
A composition contains: (a) a vinyl-functional polysiloxane; (b) a silyl hydride functional polysiloxane having on average at least two silyl hydride groups per molecule; (c) 60 to 92 weight-percent thermally conductive filler; (d) a platinum hydrosilylation catalyst; and (e) 0.05 to 2.0 weight-percent of a trialkoxy-functional polysiloxane; where the trialkoxy-functional polysiloxane has two or more trialkoxy functionalities per molecule and a number average molecular weight of 1200 or more and where weight-percents are relative to the composition weight.