Two-Component Coating Composition for Stable Thiol Crosslinking
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Solution Overview
Problem
Existing water-based coating compositions with mercapto groups suffer from unstable blends, premature reactions, and insufficient pot life, leading to issues with flexibility and chemical resistance.
Innovation Solution
A two-component coating composition comprising a water-dispersible polymer mixture with mercapto-reactive groups and a water-emulsifiable thiol, where the formation component has a Hansch parameter of at least 2.0, allowing for thermal curing and improved stability and flexibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If hydrophobic thiol component is added in substance to water-dispersible polymer, then crosslinking reaction occurs, but premature reaction (precuring) severely restricts pot life
Solution Approach 1:
The patent uses water as an intermediary phase to separate the hydrophobic thiol component from the polyurethane particles. The thiol is added as an O/W emulsion rather than in substance, preventing direct contact and premature reaction with the water-dispersible polymer until film formation occurs.
Solution Approach 2:
The coating composition is divided into two separate components that are mixed immediately before application. Component (A) contains the water-dispersible polymer with mercapto-reactive groups, while component (B) contains the hydrophobic thiol as an O/W emulsion. This segmentation prevents premature reaction while enabling crosslinking after application.
2Stability of the object's composition
If O/W emulsion stabilized with external emulsifier is used, then thiol can be dispersed in water, but emulsion is unstable and phase-separates
Solution Approach 1:
The thiol component (B) is formulated as a self-emulsifying system where the emulsion is stabilized by the thiol's own molecular structure rather than requiring external emulsifiers. This self-service approach eliminates the instability and phase separation problems associated with external emulsifiers.
3Stability of the object's composition
If water-soluble polythiols based on ethoxylated polyalcohols are used, then thiol is water-soluble, but blends are unstable and gel after just a few hours
Solution Approach 1:
The patent changes the hydrophobicity parameter of the thiol component by selecting compounds with a Hansch parameter of at least 2.0. This parameter change ensures the thiol remains hydrophobic enough to avoid premature reaction with water-dispersible polymers while still allowing crosslinking after film formation, thereby extending pot life.
4Duration of action of moving object
If SH-functional polyurethane dispersions are used with water as continuous phase, then spatial separation prevents premature reaction, but coatings are hard and lack flexibility
Solution Approach 1:
The patent creates a composite crosslinking system combining water-dispersible polyurethane with hydrophobic thiol. This composite approach allows spatial separation during storage (extending pot life) while enabling controlled crosslinking after application that produces coatings with both hardness and flexibility, overcoming the limitations of pure SH-functional polyurethane dispersions.
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 composition achieves a moderate hardness with good flexibility and high chemical resistance, while maintaining a sufficiently long pot life.
Implementation Method 1
thermally curable two-component coating compositions having mercapto groups
Implementation Method 2
crosslinking reaction as a result can only take place during or after film formation
Implementation Method 3
at least one water-emulsifiable thiol (B) comprising, as formation components
Implementation Method 4
at least one water-dispersible polymer mixture (A)
Implementation Method 5
the hydrophobic thiol component was added in substance, meaning that it cannot be excluded that significant proportions thereof diffuse into the polyurethane particles
Data Source
AI summary
A two-component coating composition comprisingat least one water-dispersible polymer mixture (A) which has at least onemercapto-reactive group selected from the group of epoxide and Michael acceptor,and alsoat least one water-emulsifiable thiol (B) comprising, as formation components,(Ba) at least one compound having at least two mercapto groups,(Bb) at least one compound having at least one mercapto-reactive group and at least one dispersing group,wherein the formation component (Ba) has a Hansch parameter of at least 2.0.