Dual Cure Silicone Composition for Scratch Resistance
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Solution Overview
Problem
Thiol-ene based dual cure compositions for elastomer and silicone rubber applications face limitations in achieving high crosslink density for hard and scratch-resistant cured compositions due to insufficient miscibility of thiol and alkene components, leading to inhomogeneous and poorly scratch-resistant results.
Innovation Solution
A silicon-free mercapto compound and phenyl-containing polyorganosiloxanes with unsaturated alkenyl and alkoxysilyl groups are combined to enhance compatibility and achieve high hardness and scratch resistance in cured silicone compositions, using a photoinitiator and moisture cure catalyst for dual curing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If thiol-containing siloxane and unsaturated siloxane reactants are used to achieve high crosslink density, then hardness is improved, but scratch-resistance deteriorates due to inhomogeneous composition
Solution Approach 1:
The patent applies homogeneity by ensuring uniform distribution of thiol and alkene functional groups throughout the siloxane composition. This is achieved by using siloxane polymers with controlled molecular weights and functional group densities, preventing phase separation and ensuring homogeneous crosslinking throughout the cured material, which simultaneously achieves hardness and scratch-resistance
Solution Approach 2:
The patent employs parameter changes by systematically adjusting the molar ratios of thiol to alkene functional groups, molecular weights of siloxane components, and concentrations of crosslinking agents. These parameter optimizations enable precise control over crosslink density while maintaining compositional homogeneity, resolving the contradiction between hardness and scratch-resistance
2Productivity
If (meth)acrylate-based curing systems are used to achieve rapid curing, then productivity is improved, but device complexity increases due to requirement of inert atmosphere
Solution Approach 1:
The patent applies the extraction principle by removing the requirement for inert atmosphere from the curing process. This is achieved by using a dual-cure system where UV photopolymerization can proceed effectively in the presence of oxygen, eliminating the need for complex inert gas handling equipment while maintaining rapid curing speeds
Solution Approach 2:
The patent employs multi-functionality by designing a curing system that can operate under multiple conditions - both in inert and non-inert atmospheres. The composition contains both (meth)acrylate groups for UV-curing and siloxane groups for moisture-curing, providing curing pathway flexibility that eliminates the need for specialized inert atmosphere equipment
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 Shore A hardness of at least 50 and Pencil Scratch Resistance of 4B, providing a hard and scratch-resistant cured silicone suitable for coatings and encapsulating materials without the need for inert curing conditions.
Implementation Method 1
Upon exposure to light the thiol functionality reacts with and adds across the double bond of the unsaturated reactant
Implementation Method 2
a linear polyorganosiloxane containing a terminally unsaturated alkenyl group, an alkoxysilyl group and phenyl groups
Implementation Method 3
The moisture cure mechanism serves to cure composition blocked from exposure to light
Data Source
AI summary
A composition contains: (a) a silicon-free mercapto compound comprising 2 or more mercapto groups; (b) a linear polyorganosiloxane containing one or more than one terminally unsaturated alkenyl group, 40 mole-percent or more phenyl groups relative to moles of silicon atoms and at least one alkoxysilyl group per molecule; (c) a resinous polyorganosiloxane containing one or more than one terminally unsaturated alkenyl group and 20 mole-percent or more phenyl groups relative to moles of silicon atoms; (d) a photoinitiator; and (e) a moisture cure catalyst; and wherein the molar ratio of mercapto groups to terminally unsaturated alkenyl groups in the composition is in a range of 0.3 to 2.0.