UV-Curable Polythioether Sealants for Aerospace Fasteners
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Solution Overview
Problem
Aerospace sealants used for fasteners and panel gaps require faster curing times, visual transparency for inspection, and meet demanding performance requirements such as flexibility, fuel resistance, and high temperature resistance, which existing thermally-curable sealants fail to provide.
Innovation Solution
UV-curable sealant compositions comprising thiol-terminated polythioethers and alkenyl-terminated compounds, such as polyvinyl ethers or polyallyl compounds, that cure rapidly under ultraviolet radiation, maintaining visual clarity and offering improved adhesion and resistance properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If thermally-curable sealants are used, then the sealant provides good adhesion and flexibility, but the curing time is too long (about two days)
Solution Approach 1:
The patent changes the curing mechanism from thermal to photopolymerization using UV radiation. The sealant composition includes photoinitiators that activate under UV light to rapidly crosslink the polymer matrix, reducing curing time from two days to minutes or seconds while maintaining adhesion and flexibility properties
Solution Approach 2:
The patent replaces the thermal curing system with a photopolymerization system. Instead of using heat to initiate and control the curing reaction, UV radiation activates photoinitiators that trigger rapid polymerization, fundamentally changing the energy input mechanism from thermal to optical
2Reliability
If thermally-curable sealants are used, then the sealant provides adequate sealing performance, but the cured sealant is opaque and visual inspection is difficult
Solution Approach 1:
The patent selects polymer matrices and additives that remain optically clear both in uncured and cured states. The photopolymerization reaction and final cured structure are designed to maintain transparency, enabling visual inspection of the sealed joint to detect defects such as voids, bubbles, or incomplete sealing
Solution Approach 2:
The patent creates different optical properties in different regions: the sealant body remains transparent for inspection, while the cured shell provides structural protection. This allows the sealing function and inspection function to coexist without compromising either
3Productivity
If preformed seal caps with partially hardened shells are used, then the sealant can be applied efficiently, but the curing process is slow and complex
Solution Approach 1:
The patent allows preformation of seal caps with a cured shell while keeping the interior sealant uncured by controlling UV exposure. This preliminary structuring enables efficient handling and application, with the understanding that final curing will occur rapidly after application through UV radiation
Solution Approach 2:
The patent employs staged curing: first UV curing to form a cured shell for structural integrity, then application of uncured sealant, and finally additional UV curing to complete the process. This periodic application of UV radiation optimizes both handling efficiency and final cure speed
4Productivity
If rapid curing is achieved, then productivity is improved, but the sealant may lose flexibility and adhesion properties
Solution Approach 1:
The patent uses composite polymer systems combining different polymer matrices (epoxies, polyesters, polyacrylates, polythioethers) with carefully selected photoinitiators and crosslinking agents. This composite approach enables rapid photopolymerization while maintaining the flexibility and adhesion characteristics of the underlying polymer system
Solution Approach 2:
The patent adjusts the molecular weight, functionality, and chemical structure of polymer components to balance cure speed with final material properties. By controlling the ratio of monomers to oligomers and selecting appropriate photoinitiator types, the patent achieves rapid curing without sacrificing the flexibility and adhesion needed for aerospace applications
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 UV-curable sealants achieve rapid curing, visual transparency, and meet aerospace performance standards, including flexibility, fuel resistance, and high temperature resistance, enabling efficient high-volume processing and inspection of sealant quality.
Implementation Method 1
UV-curable sealant compositions comprising thiol-terminated polythioethers and alkenyl-terminated compounds, such as polyvinyl ethers or polyallyl compounds, that cure rapidly under ultraviolet radiation
Data Source
AI summary
UV curable sealants, method s for making the sealants, and method for using the sealants are disclosed. The UV curable sealants may be used in seal caps useful to seal fasteners in aerospace fuel tanks. The UV curable sealants may also be used to smooth defects in surfaces such as aerospace surfaces.