Crosslinkable Polyurethane Coatings Resolving Hardness Flexibility Trade-off
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Solution Overview
Problem
Conventional water-dispersible polyurethane (PU) polymers struggle to achieve a balance between hardness and flexibility, often requiring increased isocyanate levels, which increases material costs, and they emit volatile organic compounds (VOCs), necessitating the development of low or VOC-free aqueous-based PU coating systems that cure through water evaporation.
Innovation Solution
An aqueous crosslinkable coating composition comprising a water-dispersible polyurethane polymer, a carbonyl-functional vinyl polymer, and carbonyl-reactive amine or hydrazine functional groups, where the carbonyl-functional groups are preferably in a crosslinker distinct from the polyurethane and vinyl polymer, allowing for crosslinking reactions that cure upon water evaporation, thereby achieving desired mechanical properties without high isocyanate levels and minimizing VOCs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional water-dispersible PU polymers are used to achieve good hardness and flexibility, then increased amounts of isocyanate are required, but this results in increased material costs that are prohibitive
Solution Approach 1:
The patent changes the chemical parameters of the PU polymer by incorporating cycloaliphatic groups with specific structures (X-Z-X where Z is an aliphatic ring) and controlling the types of linkage groups (ester, ether, amide, carbonate) to achieve the desired balance of hardness and flexibility without requiring excessive isocyanate content
Solution Approach 2:
The patent creates a composite PU polymer structure that combines cycloaliphatic groups with multiple types of linkage groups and functional groups (salt/salt-forming groups, ethylenically unsaturated groups) to achieve synergistic effects that provide both mechanical performance and cost efficiency
2Strength
If conventional PU coating compositions containing organic solvents are used, then suitable mechanical properties are achieved, but volatile organic compounds (VOCs) are released into the atmosphere
Solution Approach 1:
The patent changes the solvent parameter from organic solvents to water as the dispersing medium, creating water-dispersible PU polymers that maintain suitable mechanical properties while eliminating VOC emissions. This is achieved through specific polymer structure design including cycloaliphatic groups and functional groups that enable water dispersion
Solution Approach 2:
The patent converts the typically harmful role of solvents into a beneficial water-based system, where water serves as the dispersing medium instead of organic solvents, thereby eliminating harmful VOC emissions while maintaining coating performance through careful polymer structure design
3Object-generated harmful factors
If water-dispersible PU polymers are used to reduce VOC emissions, then films are formed that are hard and relatively inflexible or soft and highly flexible, but it is difficult to achieve a proper blend of both hardness and flexibility
Solution Approach 1:
The patent changes the structural parameters of the PU polymer by incorporating specific cycloaliphatic groups (X-Z-X structure with aliphatic ring Z) and controlling the composition of linkage groups (ester, ether, amide, carbonate) to achieve an optimal balance between hardness and flexibility in water-dispersible systems
Solution Approach 2:
The patent creates a composite polymer structure combining cycloaliphatic groups with multiple linkage group types and functional groups to achieve synergistic effects that provide both hardness and flexibility simultaneously, overcoming the limitation of conventional water-dispersible PU polymers that tend to be either hard/inflexible or soft/flexible
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 provides PU films with a suitable balance of hardness and flexibility while reducing material costs and VOC emissions, offering enhanced physical properties and cost efficiency in PU coating applications.
Implementation Method 1
the carbonyl-functional groups are preferably in a crosslinker distinct from the polyurethane and vinyl polymer, allowing for crosslinking reactions that cure upon water evaporation
Implementation Method 2
cure upon water evaporation
Data Source
AI summary
An aqueous crosslinkable coating composition that includes a PU polymer and a vinyl polymer bearing carbonyl groups (i.e., a carbonyl-functional vinyl polymer) and/or latex polymer. The composition also preferably includes carbonyl-reactive amine and/or hydrazine functional groups.