Thermolatent Cyclic Tin Catalysts for Polyurethane Coatings
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Solution Overview
Problem
Current polyurethane coatings face challenges with narrow processing windows due to rapid crosslinking reactions, especially when using traditional catalysts like organotin compounds, which have ecological disadvantages, and latent catalysts face issues with reproducibility and toxicity concerns.
Innovation Solution
The use of specific inorganic Sn(IV) catalysts, specifically cyclic tin compounds, which are thermolatent and do not significantly accelerate the reaction at room temperature but activate upon temperature increase, providing a wider processing window and avoiding toxic heavy metals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If traditional organotin catalysts are used to accelerate the NCO-OH reaction, then the reaction speed is improved, but the ecological profile deteriorates and the processing window is shortened
Solution Approach 1:
The patent changes the chemical composition parameter by replacing organotin catalysts with alternative catalyst systems (organobismuth, organoaluminum, or organogermanium compounds), thereby eliminating toxic heavy metals while maintaining catalytic functionality. This substitution resolves the ecological harm issue while preserving the ability to control reaction speed.
Solution Approach 2:
The patent employs catalysts that can be used in very low concentrations (0.01-5 wt%) and are consumed during the reaction process. These catalysts provide the necessary acceleration without requiring long-term persistence in the system, allowing for effective catalysis with minimal environmental burden.
2Speed
If catalysts are added to accelerate the crosslinking reaction, then the reaction speed is improved, but the processing window (open time) is shortened
Solution Approach 1:
The patent employs catalysts whose activity can be dynamically controlled through temperature-dependent activation or moisture activation. The catalysts remain relatively inactive during mixing and application at lower temperatures, preserving the processing window, then become active during curing at elevated temperatures or upon moisture exposure, providing the necessary crosslinking acceleration.
Solution Approach 2:
The catalyst components are pre-formulated in the coating composition but remain dormant during storage and application. The activation occurs preliminarily planned - either through temperature increase during curing or through controlled moisture exposure - ensuring that catalysis begins at the optimal moment without compromising the open time of the formulation.
3Loss of time
If latent catalysts activated by moisture or oxygen are used, then the processing window is extended, but the reproducibility of migration and crosslinking degree deteriorates
Solution Approach 1:
The patent employs catalyst systems that respond to feedback signals from the environment (temperature increase or moisture presence) to activate crosslinking. The catalyst activity automatically adjusts based on the actual curing conditions, ensuring that crosslinking proceeds reliably regardless of the specific activation pathway, thereby improving reproducibility across different formulations and application conditions.
4Loss of time
If photolatent catalysts are used for activation, then the processing window is extended, but the applicability to pigmented systems is limited
Solution Approach 1:
The patent replaces photolatent catalyst activation (optical mechanism) with alternative activation mechanisms such as thermal activation or moisture activation. This substitution eliminates the limitation imposed by pigment interference with light penetration, allowing the catalysts to function effectively in both clear and pigmented coating systems, thereby significantly improving versatility.
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 allows for coatings with extended processing times at room temperature and accelerated curing upon application, maintaining high quality while being free from toxic heavy metals, thus addressing ecological and toxicological issues of previous systems.
Implementation Method 1
the use of specific inorganic Sn(IV) catalysts, specifically cyclic tin compounds, which are thermolatent and do not significantly accelerate the reaction at room temperature but activate upon temperature increase
Implementation Method 2
thermolatent inorganic tin-containing catalyst
Data Source
AI summary
The present invention relates to the use of specific inorganic Sn(IV) for the production of polyisocyanate polyaddition products from a) at least one aliphatic, cycloaliphatic, araliphatic and/or aromatic polyisocyanate, b) at least one NCO-reactive compound, c) at least one thermolatent inorganic tin-containing catalyst, d) optionally further catalysts and/or activators other than c), e) optionally fillers, pigments, additives, thickeners, antifoams and/or other auxiliary substances and additives, wherein the ratio of the weight of the tin from component c) and the weight of component a) is less than 3000 ppm when component a) is an aliphatic polyisocyanate and less than 95 ppm when component a) is an aromatic polyisocyanate, wherein as thermolatent catalysts cyclic tin compounds of formula I, II or III:wherein n>1,are used.