Sulfur-Based Sealant Curing via Photoinitiator UV Activation
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Solution Overview
Problem
Conventional sealing compounds used in the aerospace industry have long curing times, leading to complex and time-consuming processes, with fast-curing options often compromising on mechanical properties and requiring high catalyst content or elevated temperatures, which are difficult to implement, especially for large or hard-to-reach substrates.
Innovation Solution
A method using a mixture of mercapto-terminated polymers with isocyanate-based hardeners and sterically hindered tertiary amine photoinitiators that cure upon exposure to high-energy actinic radiation, allowing for rapid and on-demand curing at room temperature or slightly higher temperatures, achieving a tack-free surface in minutes and complete curing within hours.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional sealants with long processing times are used, then mechanical properties and resistance to various media are maintained, but curing time becomes excessively long
Solution Approach 1:
The invention introduces a photoinitiator system that changes the curing mechanism from time-dependent chemical reaction to light-triggered rapid polymerization. By adding compounds like 2,4,6-trimethylbenzoylphosphine oxide (TPO) as photoinitiators, the sealant transitions from conventional slow curing to rapid UV-cured hardening, achieving Shore A hardness of 30 within 60 minutes while maintaining mechanical properties
Solution Approach 2:
The invention creates a composite formulation combining conventional sealant base polymers (mercapto-terminated polymers) with photoinitiator additives. This composite material system allows the sealant to exhibit both the desired mechanical properties of conventional sealants and the rapid curing characteristics of UV-curable materials, resolving the contradiction between strength and curing time
2Productivity
If catalyst content is increased to accelerate curing, then curing speed improves, but processing time is reduced and workability is compromised
Solution Approach 1:
The invention replaces the conventional chemical catalyst-based curing mechanism with a photoinitiator-based UV light curing system. This substitution allows the sealant to maintain full processing time (10-15 minutes) for application and positioning, then rapidly cure upon UV exposure without the trade-off between catalyst content and workability that plagues conventional systems
3Loss of time
If elevated temperatures are applied to speed up curing, then curing time is reduced, but implementation becomes difficult for large or hard-to-reach substrates
Solution Approach 1:
The invention substitutes thermal energy with optical energy (UV radiation) as the curing trigger. UV light can be directed precisely at the sealant application site using portable lamps or integrated coating systems, enabling rapid curing of large or hard-to-reach substrates without the logistical challenges of heating equipment and temperature control required by thermal curing methods
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
This approach significantly reduces curing times while maintaining high-quality properties such as resistance to various media and mechanical strength, enabling efficient and rapid coating of substrates with minimal heat generation and no need for elevated temperatures, thus simplifying the manufacturing and maintenance of aircraft and spacecraft.
Implementation Method 1
a mixture of an unhardened base material A and a hardener containing isocyanate, in that the base material A, the hardener or both contain at least one photoinitiator which can be activated upon exposure to high-energy actinic radiation and can release an amine radical, which acts or can act as a catalyst for curing
Data Source
AI summary
The invention relates to a method for curing a mixture of a matrix and a curing agent based on sulfur-containing polymers, said curing process being carried out on command and so rapidly that a tack-free surface of the sealant is achieved in a tack-free time of 0.05 to 5 minutes starting from the beginning of the curing process. The invention also relates to a method for coating a substrate with a mixture of a matrix and a curing agent in order to produce and cure a sealant, said matrix and curing agent containing sulfur-containing polymers. The mixture is an uncured mixture with an isocyanate content, and the matrix is uncured and contains a mercaptan-terminated base polymer based on polyether, polythioether, polysulfide, copolymers thereof, and/or mixtures thereof, wherein the uncured matrix, the curing agent, or both contain at least one photoinitiator based on sterically-inhibited tertiary amines. At least one photoinitiator releases at least one radical per tertiary amine-based molecule under the effect of high-energy actinic radiation, and an active catalyst is formed from said radical in particular by means of hydrogen absorption, said catalyst acting as a catalyst for the curing process of the sealant. The mixture cures in the temperature range of -10 to +70 °C after the high-energy actinic radiation is applied, and the mixture is referred to as a sealant starting from the beginning of the curing process. The invention further relates to corresponding matrices A, mixtures B, curing agents, sealant systems, and aircraft containing same.