Aqueous Polyurethane Hardness Solvent Resistance
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Solution Overview
Problem
Aqueous dispersions of polyurethanes lack sufficient hardness and solvent resistance in coating films, necessitating improvement in their formulation to enhance these properties.
Innovation Solution
The development of an aqueously dispersible polyurethane with specific amounts of hydroxyl groups, urea groups, and degree of branching, achieved through a process involving the reaction of hydroxy-functional polymers with polyisocyanates and additional compounds, results in a polyurethane with improved hardness and solvent resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional polyurethane dispersions are used, then the coating films can be prepared, but the hardness and solvent resistance are insufficient
Solution Approach 1:
The patent applies parameter changes by precisely controlling the specific amount of substance of hydroxyl groups (at least 0.6 mol/kg), urea groups, and degree of branching (tertiary and quaternary carbon atoms) in the polyurethane molecules. These parameter optimizations simultaneously improve both hardness and solvent resistance of the coating films.
Solution Approach 2:
The patent creates a composite molecular structure containing multiple functional groups (hydroxyl groups, urea groups, and branched aliphatic carbon atoms) within the polyurethane chains. This composite approach at the molecular level enables the coating to achieve both high hardness and excellent solvent resistance.
2Strength
If the specific amount of hydroxyl groups and urea groups is increased, then the hardness improves, but the molecular complexity increases
Solution Approach 1:
The patent optimizes the specific amount of substance of hydroxyl groups to at least 0.6 mol/kg and urea groups to specific ranges, achieving the desired hardness while controlling molecular complexity through precise parameter specification rather than arbitrary increases.
Solution Approach 2:
The patent introduces localized branching structures (tertiary and quaternary aliphatic carbon atoms) at specific positions within the polymer chains, rather than uniformly complicating the entire molecular structure. This localized approach improves hardness without proportionally increasing overall molecular complexity.
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 hardness and solvent resistance, with specific formulations achieving König hardness values over 150 seconds and acetone resistance exceeding two minutes, demonstrating improved film properties.
Implementation Method 1
reaction of hydroxy-functional polymers with polyisocyanates
Implementation Method 2
coating films prepared from these polyurethanes
Data Source
AI summary
The invention relates to an aqueously dispersible polyurethane having a specific amount of substance of hydroxyl groups, —OH, of at least 0.6 mol/kg, and additionally satisfying at least two of the following conditions: a) a degree of branching measured as specific amount of substance of tertiary and/or quaternary aliphatic carbon atoms of from 0.01 mol/kg to 0.5 mol/kg, b) a specific amount of urea groups >N—CO—N< of from 0.8 mol/kg to 2 mol/kg, and c) a specific amount of substance of hydroxyl groups, —OH, of from 1 mol/kg to 4 mol/kg, wherein in each case the specific amount of substance is based on the mass of the polyurethane, a process for the preparation thereof, and a method of use thereof.