Low Hydroxy Crosslinkable Composition for Fast Curing Coatings
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Solution Overview
Problem
Existing cross-linkable compositions face challenges in achieving a balance between fast curing and maintaining optimal coating appearance and hardness, particularly in high solid content compositions, where high catalyst levels accelerate curing but can negatively impact surface appearance and film hardness.
Innovation Solution
A cross-linkable composition with reactive components A and B, characterized by low hydroxy numbers, utilizing a carbonate salt catalyst and specific resin structures, such as malonate-containing polymers, to control the Real Michael Addition reaction, ensuring improved hardness and appearance while allowing for ambient curing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high levels of catalyst are used to achieve fast curing, then curing speed is improved, but surface appearance and film hardness are negatively affected
Solution Approach 1:
The patent changes the chemical parameters of the catalyst system by using a latent base catalyst with specific pKa values (8-14) and controlling its concentration (0.01-5% by weight). This parameter optimization allows the system to achieve fast curing while maintaining surface appearance and film hardness, resolving the contradiction between curing speed and coating quality
Solution Approach 2:
The patent applies local quality by creating different curing rates in different locations within the coating. The latent base catalyst enables controlled curing that progresses from the bulk to the surface, allowing proper levelling and surface formation before final crosslinking, thus achieving both fast overall curing and good surface appearance
2Productivity
If high levels of catalyst are used to achieve fast curing, then curing speed is improved, but film hardness development is negatively affected
Solution Approach 1:
The patent uses preliminary action by incorporating the latent base catalyst in a dormant form that activates at the appropriate time. The catalyst precursor is prepared in advance but remains inactive during application and initial drying, then activates to promote crosslinking after the coating has levelled and solvent has evaporated, ensuring proper film hardness development
Solution Approach 2:
The patent implements periodic action through the staged curing process enabled by the latent base catalyst. The curing occurs in phases: initial solvent evaporation and levelling, then progressive crosslinking as the catalyst activates, and finally complete curing. This periodic action ensures film hardness develops properly while maintaining fast overall curing speed
3Productivity
If curing occurs at the time scale of solvent evaporation, then fast curing is achieved, but surface irregularities and gas inclusions occur
Solution Approach 1:
The patent applies beforehand cushioning by using the latent base catalyst system that provides a buffer period between application and active curing. This cushioning effect allows solvent to evaporate and air bubbles to escape before the crosslinking reaction becomes vigorous, preventing surface irregularities and inclusions while maintaining fast overall curing
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 enhanced coating hardness and appearance by regulating the curing process, providing a balance between rapid curing and surface quality, especially in thick layers, with improved pot life and reduced solvent entrapment.
Implementation Method 1
Real Michael Addition is a reaction wherein a reactive component B with at least 2 activated unsaturated groups (hereafter also referred to as the RMA acceptor) and a reactive component A with at least 2 acidic protons C—H in activated methylene or methine groups (hereafter also referred to as the RMA donor) react in the presence of a strong base catalyst
Data Source
AI summary
An RMA crosslinkable composition having at least one crosslinkable component including reactive components A and B each including at least 2 reactive groups, the at least 2 reactive groups of component A being acidic protons (C—H) in activated methylene or methine groups and the at least 2 reactive groups of component B are activated unsaturated groups (C═C) and a base catalyst (C) which reactive components A and B crosslink by Real Michael Addition (RMA) reaction under action of the base catalyst, characterised in that the at least one crosslinkable component including reactive components A and B in the composition have a total hydroxy number of less than 60, preferably less than 40 and more preferably less than 20 mg KOH/g solids. Further, specific resins A and B having a low hydroxy number for use in RMA cross-linkable compositions and a process for the manufacture thereof.