Cluster Organopolysiloxane Dual Cure for Tack-Free UV Curing in Air
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Solution Overview
Problem
Existing (meth)acrylate functional organopolysiloxanes face oxygen inhibition during free radical polymerization in air, leading to wet and/or tacky composition surfaces due to slow and/or insufficient curing, requiring inert gas blankets or other measures to prevent oxygen interference.
Innovation Solution
A cluster organopolysiloxane with 50-95 mole-percent acrylate/methacrylate and 5-50 mole-percent trialkoxysilyl terminal functionalities, enabling rapid UV-induced free radical polymerization and moisture curing to achieve a dry, tack-free surface in 30 seconds or less, even in air.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If free radical polymerization is conducted in air, then the composition can be cured without inert gas protection, but oxygen inhibition occurs resulting in wet and/or tacky surfaces
Solution Approach 1:
The patent changes the chemical structure parameter of the polysiloxane by introducing a cluster structure with specific terminal functionalities (50-95 mol% acrylate/methacrylate and 5-50 mol% trialkoxysilyl groups). This structural parameter change enables the composition to achieve rapid UV curing in air that overcomes oxygen inhibition, producing dry, tack-free surfaces without requiring inert gas protection.
Solution Approach 2:
The invention creates a composite functional system by combining multiple terminal functionalities on the cluster polysiloxane: (meth)acrylate groups for UV-free radical polymerization and trialkoxysilyl groups for moisture curing. This composite functionality allows the single polymer to participate in dual curing mechanisms, with the UV cure providing rapid surface drying that prevents oxygen inhibition effects.
2Productivity
If UV light exposure is increased to improve curing speed, then surface drying accelerates, but energy consumption increases
Solution Approach 1:
The patent optimizes the chemical composition parameters of the polysiloxane, specifically the ratio and types of terminal functionalities, to achieve maximum reactivity under moderate UV conditions. The cluster structure with 50-95 mol% (meth)acrylate groups provides high UV absorption efficiency, enabling rapid curing at lower energy inputs compared to conventional linear polysiloxanes.
Solution Approach 2:
The invention achieves sufficient curing with partial UV exposure by designing a highly reactive system. The cluster polysiloxane structure with concentrated (meth)acrylate functionalities at the clusters enables the polymerization to reach completion with only 4 Joules per square centimeter of UV energy, representing a partial action approach that avoids excessive energy input while achieving the desired curing effect.
3Productivity
If cluster polysiloxane with high acrylate content is used to achieve rapid UV cure, then surface drying improves, but moisture curing capability may be reduced
Solution Approach 1:
The patent precisely controls the compositional parameters of the cluster polysiloxane, specifying 50-95 mol% (meth)acrylate groups and 5-50 mol% trialkoxysilyl groups. This parameter optimization ensures sufficient (meth)acrylate content for rapid UV curing while maintaining adequate trialkoxysilyl content for moisture curing, achieving balance between the two curing mechanisms.
Solution Approach 2:
The cluster polysiloxane is designed with multi-functionality, where a single polymer molecule possesses both (meth)acrylate groups for UV-free radical polymerization and trialkoxysilyl groups for moisture curing. This universal design enables the composition to achieve dual curing capability, with the UV portion providing rapid surface drying and the moisture portion providing continued curing throughout the bulk.
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 cures to a dry, tack-free surface in 30 seconds or less under UV exposure in air, facilitating dual curing with a UV radical initiator and moisture cure catalyst, outperforming linear polysiloxanes.
Implementation Method 1
Curing of (meth)acrylate functional organopolysiloxanes can be initiated by ultraviolet ('UV') light with UV radical initiators. The free radical induced polymerization is often used to rapidly achieve an initial cure of the surface of a composition.
Implementation Method 2
When combined with alkoxysilyl functionality, or other organopolysiloxanes having alkoxysilyl functionality, (meth)acrylate functional organopolysiloxanes can be part of a dual cure composition that partially cures by UV-induced free radical induced polymerization through the (meth)acrylate group and by moisture curing through the alkoxysilyl functionality.
Data Source
AI summary
A composition contains a cluster organopolysiloxane having the following structure:where:and R is independently in each occurrence selected from a group consisting of aryl groups and alkyl groups having from 2 to 6 carbons; R′ and R″ are independently in each occurrence selected from divalent hydrocarbon groups containing from 2 to 6 carbon atoms; n is a value in a range of 50 to less than 200; and A is independently in each occurrence selected from a group consisting of acrylate, methacrylate and trialkoxysilyl groups; provided that, on average, 50 to 95 mole-percent of the A groups are selected from acrylate and methacrylate groups and 5 to 50 mole-percent of the A groups are selected from trialkoxysilyl groups.