UV-Curable Polyurethane Coatings via Diamine Chain Extension
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Solution Overview
Problem
Current water-borne UV-curable polyurethane dispersions for wood coatings lack sufficient hardness and adhesion, especially for pigmented coatings, and have limitations in chemical resistance and flexibility, requiring high double bond densities and complex formulations.
Innovation Solution
Aqueous radiation-curable coating composition comprising aromatic, cycloaliphatic, or aliphatic diisocyanates, ethylenically unsaturated compounds, hydrophilic carboxylic acids, high molecular weight polyester polyols, low molecular weight alcohols, polyfunctional diamines, and triamines, which form a dense gel-network upon UV curing, enhancing hardness, flexibility, and chemical resistance without requiring high double bond densities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high double bond densities are used to improve hardness, then the coating achieves sufficient hardness, but the formulation becomes complex and requires high amounts of reactive diluents
Solution Approach 1:
The invention changes the chemical structure parameters of the polyurethane backbone by incorporating aromatic segments (divinyl benzene, styrene) and cycloaliphatic segments (norbornene derivatives) instead of relying on high double bond densities from reactive diluents. This structural modification provides inherent hardness while simplifying the overall formulation.
Solution Approach 2:
The invention creates a composite polyurethane structure combining aromatic segments, cycloaliphatic segments, and aliphatic segments within the same polymer backbone. This composite approach achieves hardness through the aromatic and cycloaliphatic components while maintaining flexibility and processability through the aliphatic components.
2Reliability
If conventional water-borne UV dispersions are used, then the coating can be applied, but the adhesion to substrates and chemical resistance are insufficient
Solution Approach 1:
The invention modifies the polyurethane structure by incorporating specific aromatic and cycloaliphatic segments that enhance intermolecular interactions and crosslinking density, thereby improving adhesion and chemical resistance while maintaining good application properties through controlled molecular weight and functionality.
Solution Approach 2:
The cycloaliphatic segments act as intermediaries between the rigid aromatic segments and the flexible aliphatic segments, providing a transition zone that enhances overall coating performance including adhesion and chemical resistance while maintaining processability.
3Object-affected harmful factors
If high solid content is achieved to reduce VOC, then the environmental friendliness improves, but the viscosity increases making application difficult
Solution Approach 1:
The invention changes the molecular architecture by incorporating macrocyclic structures and controlling the functionality distribution in the polyurethane chain, which reduces intermolecular entanglement and improves flow characteristics even at high solid contents, thereby maintaining low viscosity and good applicability.
4Strength
If aromatic segments are incorporated to improve hardness, then the coating hardness increases, but the formulation complexity and synthesis difficulty increase
Solution Approach 1:
The invention uses pre-synthesized macrocyclic polyols with defined structures as starting materials, which already contain the necessary functional groups and molecular architecture. This preliminary preparation simplifies the subsequent polyurethane synthesis by reducing the number of steps and improving reproducibility.
Solution Approach 2:
The invention divides the complex polyurethane synthesis into manageable segments by using pre-formed macrocyclic polyols as building blocks. This segmentation approach allows for controlled incorporation of aromatic and cycloaliphatic segments without requiring complex one-step syntheses.
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 high hardness, flexibility, and excellent adhesion to various substrates before and after UV curing, with reduced volatile organic content, low viscosity, and improved safety due to lower skin and eye irritation, making it suitable for both clear and pigmented coatings.
Implementation Method 1
radiation-curable polyurethanes are widespread... UV-curing... curable with UV radiation
Data Source
AI summary
The invention relates to aqueous polyurethane dispersions that are curable with UV radiation. The polyurethanes are chain-extended with aromatic, cycloaliphatic or aliphatic diamine compound and cross-linked with aliphatic triamine compound. The polyurethanes are useful dispersions for coating various substrates.