Solvent-Borne Polyurethane Coating VOC Reduction
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Solution Overview
Problem
Two-component solvent-based polyurethane coatings face challenges in reducing volatile organic compounds (VOCs) while maintaining physical and mechanical properties, with strategies like using lower molecular weight polyols or hydrophilic polyisocyanates leading to issues such as short pot lives, poor solvent resistance, and sensitivity to catalyst levels.
Innovation Solution
A solvent-borne two-component polyurethane coating composition using 2-propoxyethanol or 2-butoxyethanol as solvents, combined with water, to facilitate a stable dispersion of polyisocyanate in the polyol phase, allowing for efficient reaction and minimizing unreacted polyisocyanate solidification, resulting in coatings with high reactivity and good resistance to solvents and environmental influences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If lower molecular weight polyols are used to reduce VOC levels, then solvent demand is reduced, but pot life becomes short and catalyst sensitivity increases
Solution Approach 1:
The patent changes the molecular weight parameter of the polyol from low to high (5,000-50,000 g/mol), which reduces the number of hydroxyl groups per unit volume and thereby reduces the rate of reaction with water. This parameter change extends pot life while maintaining VOC compliance through the water dispersibility provided by carboxyl groups.
Solution Approach 2:
The patent creates a composite polyol system containing both hydroxyl groups (for polyurethane formation) and carboxyl groups (for water dispersibility). This composite structure allows the polyol to disperse in water without requiring low molecular weight, thereby extending pot life while maintaining the ability to form water-borne coatings.
2Adaptability or versatility
If hydrophilic polyisocyanates are used to improve emulsification, then compatibility with water dispersible polyols is improved, but water sensitivity of the coating becomes unacceptable
Solution Approach 1:
The patent uses carboxyl groups on the polyol as an intermediary that facilitates water dispersibility without requiring the polyisocyanate to be hydrophilic. The carboxyl groups act as a bridge between the hydrophobic polyurethane network and water, allowing emulsification while maintaining the hydrophobicity and water resistance of the final coating.
3Adaptability or versatility
If high shear mixing is used to disperse polyisocyanate in polyol with emulsifiers, then emulsification is achieved, but energy consumption increases and formulation space is occupied by emulsifiers
Solution Approach 1:
The patent enables the polyol to self-emulsify through its own carboxyl groups without requiring external emulsifiers or high shear mixing. The carboxyl groups provide inherent water dispersibility, allowing the polyol to form stable emulsions with water under mild mixing conditions, thereby eliminating the need for additional emulsifying agents and reducing energy consumption.
4Loss of substance
If water is added to the coating system to replace organic solvents, then VOC levels are reduced, but the NCO-water reaction competes with the isocyanate/polyol reaction
Solution Approach 1:
The patent changes the concentration parameter of water to a controlled level (5-50 wt%) and combines it with high molecular weight polyol that has limited total hydroxyl groups. This parameter control ensures that water is the dominant reactive species, allowing the NCO-water reaction to proceed without significantly competing with the isocyanate/polyol reaction, while still achieving VOC reduction.
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 solution enables the formulation of VOC-compliant coatings with improved pot life, solvent resistance, and optical and mechanical properties, achieving a high solids content and stable phase separation with reduced VOC levels.
Implementation Method 1
facilitate a stable dispersion of polyisocyanate in the polyol phase
Implementation Method 2
efficient reaction between the polyisocyanate and the polyol which minimizes the amount of unreacted polyisocyanate which might solidify from solution
Implementation Method 3
achieving a high solids content and stable phase separation with reduced VOC levels
Data Source
AI summary
The present invention relates to a solvent-borne two-component (2K) coating composition comprising: as a first component, a dispersion comprising: a hydroxyl-functional acrylate binder; a first solvent being at least one compound selected from the group consisting of 2-propoxyethanol and 2-butoxyethanol; water in an amount from 5 to 50 wt.% by weight of the composition; and, optionally at least one further organic solvent; and, as a second component, at least one crosslinking agent. More particularly, the present invention provides a solvent-borne two-component (2K) polyurethane coating composition, wherein said second component comprises at least one crosslinking agent having isocyanate groups.