Aqueously Dispersible Polyurethane with Silicon and Urea
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Solution Overview
Problem
Aqueous dispersions of polyurethanes lack sufficient solvent resistance and resistance to soiling and graffiti, necessitating an improvement in the composition and preparation process to enhance the properties of coating films.
Innovation Solution
An aqueously dispersible polyurethane is developed with specific ratios of silicon, urea groups, and degree of branching, prepared by reacting hydroxy-functional polymers with isocyanates and additional compounds, followed by dispersion in water, to achieve improved hardness, anti-graffiti properties, and solvent resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional polyurethane dispersions are used, then the coating process is simple, but the solvent resistance and resistance to soiling and graffiti are insufficient
Solution Approach 1:
The patent creates a composite polyurethane structure by incorporating silicon-containing polyols (providing solvent resistance and anti-graffiti properties) combined with hydroxy-functional polymers and crosslinking agents. This composite approach integrates multiple functional components into a single polymer system that delivers enhanced reliability against solvents and graffiti while maintaining a manageable composition for coating applications.
Solution Approach 2:
The patent systematically adjusts key parameters including the silicon content (0.1-5 mass%), the ratio of hydroxyl groups to isocyanate groups (0.5-2.0), and the molecular weight distribution of polyol components. By optimizing these parameters, the invention achieves improved solvent resistance and anti-graffiti properties while controlling the complexity of the overall system for practical coating applications.
2Strength
If higher crosslinking density is used to improve hardness and solvent resistance, then the coating film becomes more resistant to solvents and graffiti, but the viscosity of the dispersion increases
Solution Approach 1:
The patent introduces localized crosslinking regions within the polyurethane matrix by using multifunctional crosslinking agents that create discrete crosslink points rather than uniform crosslinking throughout. This local quality approach allows the formation of hard, solvent-resistant domains while maintaining a more flexible overall structure that preserves lower viscosity and easier applicability.
Solution Approach 2:
The patent segments the crosslinking function by using separate crosslinking agents that react with hydroxyl groups at controlled ratios. This segmentation allows independent optimization of crosslinking density (for hardness) and molecular weight between crosslinks (for viscosity), enabling the achievement of high hardness with controlled viscosity through separate parameter adjustment.
3Reliability
If more silicon-containing polyol is added to improve anti-graffiti properties, then the resistance to graffiti and soiling increases, but the cost and complexity of the composition increase
Solution Approach 1:
The patent optimizes the silicon content parameter within a specific range (0.1-5 mass%) to achieve the minimum effective concentration for anti-graffiti properties. By establishing this optimal parameter range, the invention balances the anti-graffiti performance with compositional simplicity, avoiding both insufficient protection and excessive complexity or cost associated with higher silicon concentrations.
Solution Approach 2:
The silicon-containing polyol serves multiple functions simultaneously: it provides anti-graffiti properties, enhances solvent resistance, and contributes to the overall polymer network structure. This multi-functionality reduces the need for separate additives, thereby maintaining compositional simplicity while achieving multiple performance benefits including anti-graffiti protection.
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 resulting polyurethane coatings exhibit enhanced solvent resistance, anti-graffiti properties, and improved adhesion on various substrates, including polymer films, while maintaining low viscosity and VOC content.
Implementation Method 1
reacting hydroxy-functional polymers with isocyanates and additional compounds
Implementation Method 2
followed by dispersion in water
Data Source
AI summary
The invention relates to an aqueously dispersible polyurethane having a specific amount of silicon n(Si)/m(PU) of from 0.05 mol/kg to 1 mol/kg, and a specific amount of urea groups, n(U)/m(PU), >N—CO—N< of from 0.8 mol/kg to 2 mol/kg, wherein in each case the specific amount of substance is calculated as the ratio of the amount of substance n of the entity under consideration, to the mass m(PU) of the polyurethane, to a process for the preparation thereof, and a method of use thereof.