Dual-Initiator Thiol-Ene Sealant for Shadow Cure and Open Time

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Solution Overview

Problem

Thiol-ene sealant compositions face challenges with inadequate surface curing, especially in shadowed areas or when filled with opaque materials, leading to issues with productivity and shelf stability, particularly in aerospace applications where structural integrity is critical.

Innovation Solution

Combining a thermal initiator, such as an organoborane-amine complex and a peroxide, with a photoinitiator in thiol-ene-based sealant compositions to achieve satisfactory open time, on-demand curing, and effective shadow curing without the need for a decomplexing agent.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Duration of action of moving object

If photoinitiators are used for curing, then long open time and rapid cure are achieved, but shadow regions (between opaque substrates or with opaque fillers) cannot be cured

Engineering Contradiction:

Improveopen timeVSAvoidcure completeness in shadow regions

Core Design Contradiction:

Duration of action of moving objectVSReliability

Solution Approach 1:

The patent combines photoinitiators and thermal initiators into a single sealant composition. The photoinitiator enables rapid curing and long open time where light penetrates, while the thermal initiator ensures complete curing in shadow regions by activating through heat, thus resolving the contradiction between rapid surface cure and shadow region cure.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The invention creates a composite initiator system comprising both photoinitiator and thermal initiator components. This composite approach allows the sealant to benefit from both photopolymerization (fast, controllable) and thermal polymerization (omnidirectional, shadow-penetrating) mechanisms simultaneously.

Inventive Principle:

Principle #40Composite materials

2Reliability

If thermal initiators are used for curing, then shadow regions can be cured, but excessive cure time and inadequate shelf stability occur

Engineering Contradiction:

Improvecure completeness in shadow regionsVSAvoidcure time

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

By merging photoinitiator and thermal initiator in the same composition, the photoinitiator component provides rapid curing action that reduces overall cure time, while the thermal initiator maintains the capability to cure shadow regions. The synergistic combination eliminates the excessive cure time associated with thermal initiators alone.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The photoinitiator provides sufficient curing action for most of the sealant (where light reaches), allowing the thermal initiator to operate at reduced levels specifically for shadow regions. This partial reliance on each initiator type optimizes both speed and completeness without excessive cure time.

Inventive Principle:

Principle #16Partial or excessive action

3Duration of action of moving object

If long open time is achieved with photoinitiators, then rapid cure is possible, but productivity during manufacturing decreases

Engineering Contradiction:

Improveopen timeVSAvoidmanufacturing productivity

Core Design Contradiction:

Duration of action of moving objectVSProductivity

Solution Approach 1:

The dual-initiator system enables a two-stage curing approach: initial rapid curing by photoinitiator provides immediate structural integrity (enabling faster handling and assembly), followed by complete curing by thermal initiator. This periodic action pattern improves manufacturing throughput while maintaining long open time for positioning.

Inventive Principle:

Principle #19Periodic action

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 provides a curable sealant with improved surface curing, maintaining structural integrity and productivity while ensuring adequate shelf stability, even in shadowed regions, thus addressing the chronic problem of inadequate surface cure.

Implementation Method 1

e) from 0.01 to 10 weight percent of a photoinitiator system capable of generating free radicals upon exposure to actinic radiation

Methodology Applied

Scientific EffectPhotopolymerisation: Photopolymerisation

Implementation Method 2

c) from 0.01 to 8 weight percent of at least one organoborane-amine complex; d) from 0.05 to 10 weight percent of at least one organic peroxide

Methodology Applied

Scientific EffectThermal initiation:

Data Source

PatentEP3688068B1Curable sealant compositions, seal cap, and methods of making and using the same

Publication Date: 2022.06.01 3M INNOVATIVE PROPERTIES CO

Figure 1~2

AI summary

Curable sealant compositions comprise the components: a) x weight percent of at least one polythiol; b) y weight percent of at least one unsaturated compound having at least two non-aromatic carbon-carbon double bonds, at least one carbon-carbon triple bond, or a combination thereof; c) from 0.01 to 8 weight percent of at least one organoborane-amine complex; d) from 0.05 to 10 weight percent of at least one organic peroxide; and e) from 0.01 to 10 weight percent of a photoinitiator system capable of generating free radicals upon exposure to actinic radiation. Each of x and y represents a positive real number. The sum x + y is in the range of 72 to 99. The weight percent ranges of the components a) – e) are based on the total weight of the components a) – e). A seal cap including the curable sealant composition and methods of making and using the curable sealant compositions are also disclosed.