Blocked Amine Curing Aid for Low-Monomer Polyurethane
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Solution Overview
Problem
Polyurethane compositions with low monomeric diisocyanate content, especially those based on sterically hindered and/or aliphatic diisocyanates, exhibit slow curing and poor curing characteristics, leading to tacky surfaces and reduced stability, particularly in outdoor applications.
Innovation Solution
The use of blocked amines as curing aids in polymers containing isocyanate groups with low monomeric diisocyanate content, particularly those derived from isophorone diisocyanate, enables rapid and faultless curing without significant residual tack and reduces the need for toxic catalysts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If monomeric diisocyanate is used in excess in the preparation of the polymer and then removed by distillation, then the polymer has low viscosity and low residual monomeric diisocyanate content, but the polymer cures more slowly with moisture leading to retarded strength development and long-term tackiness
Solution Approach 1:
A blocked amine is introduced as an intermediary substance that mediates the curing process. The blocked amine reacts with moisture to release free amine, which then catalyzes the reaction between isocyanate groups and water. This intermediary mechanism enables rapid curing of low-monomer polymers without requiring excess monomeric diisocyanate, thus maintaining safety while improving productivity
Solution Approach 2:
The invention changes the chemical parameters of the system by introducing blocked amines with specific structures (oxazolidine, aldimine, or hydrazide groups) that have different reactivity characteristics. This parameter change allows the curing process to be accelerated without increasing the harmful monomeric diisocyanate content, resolving the contradiction between safety and curing speed
2Stability of the object's composition
If polymers based on sterically hindered and/or aliphatic diisocyanates with low monomer level are used, then weathering stability is improved, but curing characteristics deteriorate with tacky surfaces and reduced stability
Solution Approach 1:
The blocked amine acts as a mediator that enables the curing of weathering-stable polymers based on sterically hindered and/or aliphatic diisocyanates. By providing an alternative curing mechanism that does not rely on excess monomeric diisocyanate, the blocked amine allows these polymers to achieve proper curing performance while maintaining their superior weathering stability
Solution Approach 2:
The invention creates a composite system combining the weathering-stable polymer matrix with blocked amine curing aids. This composite approach leverages the advantages of both components: the polymer provides weathering resistance while the blocked amine ensures reliable curing performance, eliminating the tackiness and stability issues of low-monomer polymers
3Productivity
If large amounts of catalyst are used to accelerate curing of low monomer level polymers, then curing speed is improved, but heat stability deteriorates due to high catalyst content
Solution Approach 1:
The blocked amine functions as a temporary catalytic agent that is consumed during the curing process. Unlike permanent metal catalysts that remain in the cured product and compromise heat stability, the blocked amine is transformed during curing, leaving minimal residual impact on the final product's stability properties
Solution Approach 2:
The invention changes the type of catalytic agent from metal-based catalysts to organic blocked amines with different stability characteristics. This parameter change allows acceleration of curing speed while maintaining heat stability, as the blocked amine decomposes or transforms during curing rather than remaining as a stable residual catalyst
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
This approach results in moisture-curing polyurethane compositions with excellent storage stability, rapid curing, high elasticity, and improved stability to weathering influences, making them suitable for exposed outdoor applications without the need for hazardous labeling.
Implementation Method 1
The blocked amine is hydrolysed by moisture with release of the free amine
Implementation Method 2
The free amine formed catalyses the reaction of isocyanate groups with moisture or water
Implementation Method 3
crosslink through reaction of isocyanate groups with moisture or water and cure to give elastomers
Data Source
AI summary
A blocked amine as curing aid for polymers containing isocyanate groups and having a low monomeric diisocyanate content, obtained from the reaction of at least one monomeric diisocyanate with at least one polyol in an NCO/OH ratio of at least 3/1, followed by removal of a majority of the monomeric diisocyanates by means of a suitable separation method, and to the moisture-curing polyurethane compositions obtained from this use. The use enables storage-stable, moisture-curing polyurethane compositions which can be safely handled even without special safety precautions and can be sold without hazard labeling in many countries, have good processibility and cure reliably and rapidly at ambient temperatures to give a material of high strength, elasticity and extensibility, and high stability to weathering influences. Such moisture-curing polyurethane compositions are particularly suitable as elastic sealants, adhesives or coatings, especially also for exposed outdoor applications.