Polythiol Sealant Cure-on-Demand and Color Control
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Solution Overview
Problem
Traditional polythiol-based aerospace sealants face challenges with curing behavior, including a tacky surface that requires stoppage of work to avoid contamination, and color issues during photocuring, which do not meet industry specifications for visual confirmation of mixing and color appearance.
Innovation Solution
Development of cure-on-demand sealant compositions using polythiols with a base-catalyzed thiol-epoxy or thiol-ene cure, incorporating a photogenerated amidine species for faster curing and colorants that provide visual contrast without red or pink hues, ensuring the sealant is tack-free and meets industry color requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional oxidative cure is used, then excellent physical properties are achieved, but the sealant surface remains tacky for hours requiring stoppage of work
Solution Approach 1:
The curing process is segmented into two independent pathways: a slow background cure that provides initial set and a fast photocure that completes the curing on demand. This allows the sealant to achieve tack-free status quickly while maintaining the option for complete curing later, resolving the contradiction between physical property development and work continuity.
Solution Approach 2:
The sealant system transitions from a static, time-dependent cure process to a dynamic, on-demand cure process. The photocure mechanism allows the user to control the curing timing, transforming the sealant from a passive material that cures automatically over hours to an active material that can be cured immediately when needed, thereby maintaining productivity while achieving excellent physical properties.
2Productivity
If photocuring is used to achieve tack-free surface, then work can continue, but the sealant surface turns red or pink which does not meet industry specifications
Solution Approach 1:
A colorant is introduced as an intermediary substance that masks the red or pink coloration caused by photocuring. The colorant absorbs or reflects light in a way that conceals the underlying color change, allowing the sealant to meet industry color specifications while still providing the beneficial photocure functionality for maintaining productivity.
Solution Approach 2:
The system intentionally utilizes and then conceals color changes during photocuring. By adding a colorant that provides visual contrast and masks the red/pink hues, the patent accepts the necessary color change during curing while presenting a compliant final appearance, thereby maintaining both productivity and color specification compliance.
3Ease of manufacture
If no colored metal oxidizing agent is used, then the two-part formulation is easier to mix, but visual confirmation of mixing becomes difficult
Solution Approach 1:
The patent introduces colorants in the sealant formulation that provide visual contrast between the two parts and indicate mixing completion. These colorants create a visible change when the parts are mixed, allowing workers to easily detect and confirm proper mixing without requiring colored metal oxidizing agents, thus maintaining ease of manufacture while solving the detection problem.
4Duration of action of stationary object
If conventional sealants are used, then long open time is achieved, but contamination of sealant surface with metal shavings occurs
Solution Approach 1:
The sealant is prepared with a slow background cure rate that provides sufficient open time for application, but the system is pre-equipped with a fast photocure mechanism. This preliminary preparation allows the sealant to remain workable longer without contamination while providing a quick cure option that can be activated immediately if contamination is a concern, effectively resolving the contradiction between extended open time and contamination prevention.
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 allows for a tack-free surface on demand, addresses color issues by providing visual confirmation of mixing, and ensures compliance with industry specifications, maintaining a suitable depth of cure and preventing leaching into fuels or wash water.
Implementation Method 1
The faster cure-on-demand functionality, which allows a tack-free skin to form upon the application of blue light, is introduced via a photogenerated amidine species
Implementation Method 2
a colorant that substantially reflects or substantially transmits light over the wavelength range from 350 nm to 500 nm
Implementation Method 3
The moderate-speed background cure (to achieve 2 h open time if sealant is left undisturbed) is effected through the inclusion of a tertiary amine catalyst on one side of the two-part formulation
Data Source
AI summary
Provided are sealant compositions that include a first component and second component. The first component contains a polysulfide, a polythioether, or a copolymer or combination thereof containing pendant or terminal thiol groups, while the second in component contains an ethylenically-unsaturated compound and either the first or second component further contains a photoinitiator. Alternatively, the second component can contain a polyepoxide and either the first or second component can contain a photolatent base and a photosensitizer. The first or second component further contains a colorant that substantially reflects or substantially transmits light over the wavelength range from 350 nm to 500 nm. These compositions can provide cure-on-demand sealant formulations that comply with Class B sealant regulations on color, provide an acceptable depth of cure, and allow two-part mixing to be easily distinguishable.