Cycloaliphatic Aldimine Mixture for Low-Isocyanate Polyurethane Strength
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Solution Overview
Problem
Elastic moisture-curing polyurethane compositions with low isocyanate content, particularly those based on cycloaliphatic isophorone diisocyanate, suffer from limited mechanical properties such as tensile strength and modulus of elasticity, and remain tacky under outdoor weathering conditions.
Innovation Solution
A mixture of isomeric cycloaliphatic aldimines with a specific isomer ratio of trans,trans to cis,trans and cis,cis in the range of 5/95 to 30/70, which are liquid at room temperature, is used to enhance the mechanical strength and elasticity of these compositions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If monomeric isophorone diisocyanate is removed from the isocyanate-functional polymer to reduce toxicity and volatility, then health and safety improve, but mechanical properties such as tensile strength and modulus of elasticity deteriorate
Solution Approach 1:
The invention changes the isomer composition parameter of the cycloaliphatic amine mixture, specifically maintaining a trans,trans isomer content between 30-70% in the aldimine mixture. This parameter optimization enables the system to achieve both low monomeric isocyanate content (<0.1 wt%) and improved mechanical properties, resolving the contradiction between health safety and mechanical strength
Solution Approach 2:
The invention uses a composite approach by combining isocyanate-functional polymers with a specifically formulated mixture of isomeric cycloaliphatic aldimines. This composite system allows the polymeric isocyanate to provide mechanical strength while the controlled isomer mixture of aldimines enables proper curing, achieving both safety and performance requirements
2Strength
If non-monomeric isocyanates such as isophorone diisocyanate oligomers are added to compensate for low isocyanate content, then mechanical strength improves, but the cured composition becomes too stiff with reduced elongation
Solution Approach 1:
The invention optimizes the isomer composition parameter of the aldimine mixture, specifically controlling the trans,trans isomer content between 30-70%. This parameter control enables the system to achieve adequate tensile strength while maintaining high elongation (>200%), preventing the unwanted stiffening effect that occurs with conventional oligomeric isocyanates
3Strength
If the isomer ratio of trans,trans to cis,trans and cis,cis is increased to improve mechanical strength, then tensile strength improves, but the composition becomes more prone to cracking and degradation
Solution Approach 1:
The invention identifies and optimizes a specific parameter range for trans,trans isomer content (30-70%) in the aldimine mixture. This optimized parameter range achieves the optimal balance between mechanical strength and reliability, preventing both insufficient strength and excessive brittleness that lead to cracking and degradation under outdoor weathering conditions
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 isomeric aldimine mixture improves tensile strength and modulus of elasticity, allowing for fast curing to non-tacky, elastic materials suitable for outdoor applications with high UV exposure and weather resistance, while maintaining low monomeric isocyanate content for safety.
Implementation Method 1
They react with isocyanate groups upon contact with moisture
Implementation Method 2
react with isocyanate groups... improve the curing properties
Implementation Method 3
the cycloaliphatic amine mixture from which the aldimine is derived, and the aldimine mixture itself, are liquid at room temperature
Implementation Method 4
affords an improved mechanical strength to elastic coatings, sealants or adhesives... cure quickly to form elastic materials
Data Source
AI summary
The present invention describes a mixture of isomeric aldimines of the formulae (Ia), (Ib) and (Ic) in which the ratio of the trans,trans isomer (Ia) to the sum of the cis,trans isomer (Ib) and the cis,cis isomer (Ic) is in the range of 5/95 to 30/70, and its use as latent hardener for moisture-curing isocyanate-functional polyurethane compositions. The inventive mixture of isomeric aldimines enables polyurethane compositions with very low content of monomeric isophorone diisocyanate and excellent stability under outdoor wheathering conditions and high UV load, which cure quickly to an elastic material of low surface tack and good mechanical properties, particularly in terms of high tensile strength and modulus of elasticity at high elongation. Such compositions are particularly suitable as elastic adhesives and/or sealants or elastic coatings, particularly for outdoor use such as on roofs, floors or ships.