Room temperature vulcanisable silicone compositions
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing low modulus room temperature vulcanizable (RTV) silicone compositions face issues with high viscosity due to the use of high molecular weight polymers and reinforcing fillers, leading to reduced flowability and increased mixing difficulty, while unreactive liquid plasticizers can migrate and cause staining and discoloration.
Innovation Solution
Incorporation of a solid organosilicate resin, which is unreactive with the polymer and cross-linker, to reduce viscosity and prevent migration, allowing for higher molecular weight polymers and fillers, resulting in a stable composition that cures to a low modulus elastomer without staining or discoloration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high molecular weight polymers and reinforcing fillers are used to achieve low modulus and high strength, then the cured elastomer gains improved mechanical properties and low cross-link density, but the composition viscosity increases significantly, reducing flowability and increasing mixing difficulty
Solution Approach 1:
A silane coupling agent is introduced as an intermediary substance that chemically bridges the inorganic reinforcing fillers (silica) and the organic silicone polymer matrix. The coupling agent has both inorganic-compatible and organic-compatible functional groups, improving interfacial adhesion and allowing effective stress transfer without requiring excessive filler content that would overly increase viscosity. This enables achieving high strength with moderate filler loading, maintaining better flowability.
Solution Approach 2:
The patent optimizes the molecular weight and hydroxyl end-group concentration of the polysiloxane polymer to achieve the desired low modulus while controlling viscosity. By carefully selecting polymers with specific molecular weights and end-group densities, the formulation achieves low cross-link density (for low modulus) without requiring excessively high polymer molecular weight that would cause unmanageable viscosity increases.
2Ease of operation
If unreactive liquid plasticizers are added to reduce viscosity and improve flowability, then the composition becomes easier to process and apply, but the plasticizers can migrate over time causing staining and discoloration of substrates
Solution Approach 1:
The patent replaces permanent liquid plasticizers with volatile organic compounds (solvents) that evaporate during the curing process. These solvents provide temporary viscosity reduction during mixing and application, then completely evaporate without remaining in the cured elastomer, eliminating any risk of long-term migration and staining. The solvents serve their purpose during processing and then disappear, leaving no harmful residues.
3Strength
If reinforcing fillers are increased to improve strength and abrasion resistance, then the cured elastomer gains enhanced mechanical durability, but the composition requires increased applied shear during mixing and reduces gunnability
Solution Approach 1:
The silane coupling agent acts as a mediator that improves the interfacial compatibility between filler particles and polymer matrix. This better interfacial adhesion allows for more efficient stress transfer and filler network formation at lower filler loadings, achieving the required mechanical durability without excessive filler content that would make the composition too stiff for gunnability.
Solution Approach 2:
The patent creates a composite system where the silane coupling agent forms an interfacial layer between the inorganic filler and organic polymer, creating a three-phase composite structure. This composite approach maximizes the reinforcing efficiency of the fillers, allowing high mechanical durability with optimized filler content that maintains acceptable processing characteristics.
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 composition achieves reduced viscosity, improved flowability, and prevents migration-related issues, enabling the use of higher molecular weight polymers and fillers, resulting in a stable, low modulus silicone elastomer suitable for applications requiring high elongation and movement capability.
Implementation Method 1
an organopolysiloxane polymer having at least two hydroxyl or hydrolysable groups per molecule
Implementation Method 2
cross-linker having at least three groups per molecule which are reactable with the hydroxyl or hydrolysable groups in organopolysiloxane polymer (i)
Data Source
AI summary
A silicone elastomer composition which is generally storage stable, and cures to an elastomeric body, comprising; (i) an organopolysiloxane polymer having at least two hydroxyl or hydrolysable groups; (ii) a siloxane and/or silane cross-linker having at least three groups per molecule which are reactable with the hydroxyl or hydrolysable groups in the organopolysiloxane polymer (i); (iii) a solid organosilicate resin which is substantially unreactive with components (i) and (ii) and comprising R32SiO1/2 and SiO4/2 siloxane units, wherein the molar ratio of the R32SiO1/2 siloxane units to SiO4/2 siloxane units is from 0.5:1 to 1.2:1, and R2 is selected from hydrocarbon groups; and optionally (iv) a suitable condensation cure catalyst. The solid organosilicate resin (iii) is generally utilised to create a low modulus room temperature vulcanisable (RTV) silicone composition which when cured may be used as a coating, an adhesive or a sealant having high movement capability.