Two-Part Water-Borne Coating for Moderate-Bake Crosslinking
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Solution Overview
Problem
Existing water-borne coating compositions for automotive refinishing face challenges in achieving proper crosslinking and curing under moderate or low baking conditions, requiring stringent drying processes and potentially incorporating volatile organic co-solvents to mitigate drying properties, which may not comply with stringent VOC regulations.
Innovation Solution
A two-part water-borne coating composition comprising a binder part with a hydroxyl-functional (meth)acrylate copolymer and a crosslinker part with pendant NCO groups, formulated to have a molar ratio of active hydrogen atoms to NCO groups between 5:1 to 1:5, using specific monomer ratios to facilitate crosslinking under moderate baking conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If water-borne coating compositions are used to reduce VOC emissions, then VOC compliance is improved, but drying requires stringent baking conditions which increases energy consumption and process complexity
Solution Approach 1:
The patent changes the chemical composition parameters of the coating system by incorporating specific monomers (vinyl aromatic monomers, unsaturated acid functional monomers) and controlling the molar ratio of active hydrogen atoms to NCO groups (5:1 to 1:5). These parameter changes enable the water-borne coating to achieve proper crosslinking and curing under moderate baking conditions, reducing the energy required while maintaining VOC compliance
Solution Approach 2:
The patent creates a composite coating system combining hydroxyl-functional (meth)acrylate copolymer with polyisocyanate crosslinker, and further incorporates specific monomer components (vinyl aromatic, unsaturated acid functional). This composite material approach enables synergistic effects where the combination of components allows crosslinking under moderate conditions, resolving the contradiction between VOC reduction and energy consumption
2Object-affected harmful factors
If water-borne coating compositions are used to reduce VOC emissions, then VOC compliance is improved, but crosslinking and curing become difficult to achieve under moderate conditions
Solution Approach 1:
The patent optimizes chemical parameters including the molar ratio of active hydrogen atoms to NCO groups (set to 5:1 to 1:5) and incorporates specific monomer types (vinyl aromatic, unsaturated acid functional) to ensure reliable crosslinking and curing occurs under moderate baking conditions, thereby maintaining VOC compliance without sacrificing curing reliability
Solution Approach 2:
The patent uses water as an intermediary medium that enables the coating to be water-borne (reducing VOCs) while the specific monomer components and controlled molar ratio act as mediators that facilitate crosslinking despite the presence of water, allowing moderate baking conditions to achieve reliable curing
3Productivity
If volatile organic co-solvents are added to mitigate drying properties, then drying performance is improved, but VOC compliance deteriorates
Solution Approach 1:
The patent extracts and eliminates the need for volatile organic co-solvents by incorporating alternative monomer components (vinyl aromatic monomers, unsaturated acid functional monomers) that enable adequate drying and crosslinking performance without VOCs, thus removing the harmful substance while maintaining productivity
Solution Approach 2:
The patent changes the compositional parameters by replacing VOC-based co-solvents with water-borne monomer components, specifically controlling the molar ratio of active hydrogen to NCO groups and incorporating non-VOC monomers, thereby achieving drying performance without VOC emissions
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 good leveling and optical properties suitable for clear coating applications, allowing for dehydration under moderate baking conditions without the need for volatile organic co-solvents, thus complying with VOC regulations.
Implementation Method 1
The crosslinker part of the composition comprises at least one polyisocyanate compound having pendant—NCO groups. The composition achieves good leveling and optical properties suitable for clear coating applications, allowing for dehydration under moderate baking conditions
Implementation Method 2
water-borne compositions must dehydrate for proper crosslinking and curing to occur. Given its boiling point, the removal of water can be difficult to achieve though flash drying
Data Source
AI summary
A two-part water-borne coating composition includes water, a) a binder part comprising (a1) a water-dilutable hydroxyl-functional (meth)acrylate copolymer; and b) a crosslinker part comprising a polyisocyanate compound having pendant—NCO groups, wherein the (meth)acrylate copolymer is the reaction product of a monomer mixture comprising, based on the total weight of monomers of the monomer mixture: from 20 to 60 wt. % of i) a hydroxyl functional adduct of a monoepoxyester and an unsaturated carboxylic acid; from 10 to 30 wt. % of ii) a hydroxyl functional unsaturated monomer different from component i); from 2 to 6 wt. % of iii) an acid functional monomer; from 20 to 60 wt. % of iv) a (meth)acrylate monomer represented by Formula H2C═CGaCO2Ra (MA); from 0 to 15 wt. % of v) a vinyl aromatic monomer; and from 0 to 20 wt. % of vi) an unsaturated monomer that is different from monomer components i) to v).