Thiol-Functional Waterborne Coating Composition for Balanced Curing
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Solution Overview
Problem
Existing water-borne coating compositions face challenges in achieving a balance between curing rate, pot life, and film appearance, with increased curing rate often leading to decreased pot life and film imperfections due to carbon dioxide formation.
Innovation Solution
A water-borne coating composition comprising a thiol-functional compound with a molar ratio of isocyanate groups to thiol groups ranging between 1:0.0001 and 1:0.4, which improves curing rate, extends pot life, and enhances film appearance without the use of ultraviolet radiation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If curing catalysts are added to increase curing rate, then curing rate is improved, but pot life decreases
Solution Approach 1:
A thiol-functional compound acts as an intermediary substance that selectively catalyzes the isocyanate-thiol reaction without significantly catalyzing the isocyanate-water reaction. This mediator enables accelerated curing through the thiol pathway while leaving the water reaction (which controls pot life) largely unaffected, thus resolving the contradiction between curing rate and pot life
Solution Approach 2:
The invention changes the chemical parameters of the curing system by introducing a thiol-functional compound with specific molecular structure and reactivity characteristics. This parameter change creates a selective catalytic effect where the thiol groups preferentially react with isocyanate groups, providing a mechanism for accelerated curing that does not proportionally accelerate the water reaction, thereby extending pot life while improving curing rate
2Speed
If curing catalysts are added to increase curing rate, then curing rate is improved, but film appearance deteriorates due to carbon dioxide formation
Solution Approach 1:
The invention converts the potentially harmful effect of catalysts (which cause carbon dioxide formation and film defects) into a beneficial effect by using a thiol-functional compound that provides selective catalysis. The thiol groups offer an alternative reaction pathway that accelerates curing without the harmful side reactions (carbon dioxide evolution) associated with conventional catalysts, thus transforming a harmful catalytic effect into a beneficial one
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 coating composition achieves a superior balance of high curing rate, long pot life, and good film appearance, outperforming prior art compositions by maintaining these properties without compromising on curing speed or film quality.
Implementation Method 1
The curing rate of such compositions can be increased to a desirable level by the addition of curing catalysts, which accelerate the isocyanate hydroxyl polyaddition reaction
Implementation Method 2
a water borne coating composition comprising a polyol and a polyisocyanate crosslinker
Data Source
AI summary
The invention relates to a water borne coating composition comprising a) a polyol, b) a polyisocyanate crosslinker, and c) a thiol functional compound, wherein the molar ratio of isocyanate groups to thiol groups ranges between 1:0.0001 and 1:0.4. The invention further relates to the use of the coating composition, and to a kit of parts for preparation of the coating composition. The coating composition according to the invention displays a balance of high curing rate, long pot life, and good film appearance of the coating prepared from it.