Latent Catalyst for Water-Based Coatings
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Solution Overview
Problem
Current two-component coating compositions based on hydroxyl-functional binders and polyisocyanate cross-linking agents face challenges in achieving a balance between acceptable processing time (pot life) and short drying time, especially in water-based systems, which can result in surface defects like bubbles or pinholes due to secondary reactions and require additional equipment for photo-latent catalysts.
Innovation Solution
A water-based two-component coating composition incorporating an organo-metal catalyst compound with an oligomeric or polymeric binder having a glass transition temperature above the application temperature, allowing for controlled curing and extended pot life without surface defects, by using a catalyst compound that is latent and becomes active during film formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If catalysts are used to reduce drying time, then drying time is improved, but pot life is reduced
Solution Approach 1:
The catalyst is pre-loaded into the base coat layer before application, but remains inactive during the pot life period. The catalyst performs its cross-linking function only after the clear coat is applied and during the drying phase, thus extending usable pot life while achieving rapid drying.
Solution Approach 2:
The base coat layer acts as an intermediary carrier for the catalyst. Instead of adding catalyst directly to the clear coat (which would reduce pot life), the catalyst is embedded in the base coat and migrates into the clear coat during drying, mediating the cross-linking reaction at the appropriate time.
2Duration of action of moving object
If catalyst is introduced into another layer to avoid affecting pot life, then pot life is improved, but control over catalyst migration is difficult
Solution Approach 1:
The catalyst is localized in the base coat layer with specific properties (water solubility, concentration range of 0.01-5% by weight). This local placement with controlled characteristics enables predictable migration into the clear coat without compromising pot life, balancing both benefits.
Solution Approach 2:
By controlling the catalyst concentration within a specific range (0.01-5% by weight) and selecting water-soluble catalysts, the migration rate and cross-linking speed are optimized. This parameter control prevents under-catalyzing (insufficient drying) and over-catalyzing (too fast reaction).
3Manufacturing precision
If flash-off time is extended to reduce bubbles, then surface quality is improved, but total process time is increased
Solution Approach 1:
The catalyst enables continuous cross-linking reaction during the drying phase without interruption. Instead of requiring a separate extended flash-off period followed by drying, the catalyzed reaction proceeds continuously and rapidly, achieving both bubble reduction and time efficiency.
Solution Approach 2:
The catalyst acts as an accelerator for the cross-linking reaction, similar to how strong oxidants accelerate chemical reactions. This catalytic acceleration allows the drying and curing process to complete rapidly, eliminating the need for extended flash-off times while maintaining high surface quality.
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 solution enables short total drying times with improved surface quality and extended pot life, maintaining the same overall drying time as prior art while preventing surface defects, and allows for better control over the curing process.
Implementation Method 1
at least one catalyst compound comprising I) at least one organo-metal catalyst for the curing reaction between isocyanate groups and functional groups reactive towards isocyanate groups
Implementation Method 2
at least one oligomeric or polymeric binder compound having a glass transition temperature Tg of ≥ 20 °C, measured by DSC (differential scanning calorimetry) at a heating rate of 10 K/min
Data Source
AI summary
The invention relates to catalyst compounds for water-based two-component coating compositions comprising: I) at least one organo-metal catalyst for the curing reaction between isocyanate groups and functional groups reactive towards isocyanate groups and II) at least one oligomeric or polymeric binder compound having a glass transition temperature Tg of =20° C, measured by DSC (differential scanning calorimetry) at a heating rate of 10 K/min, wherein the glass transition temperature Tg of binder compound II) is above the temperature at which a water-based two-component coating composition comprising the catalyst compound is applied, preferably is at least 10° C, more preferred at least 20° C above the temperature at which said two-component coating composition is applied.