Thiol-Modified Polyurethane Composition for Fast Curing and Long Pot Life
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Solution Overview
Problem
Existing two-component polyurethane compositions face challenges in achieving a combination of long pot life and rapid curing, particularly when using low monomeric diisocyanate content, which is necessary due to environmental and regulatory concerns, while maintaining high mechanical strength and elasticity.
Innovation Solution
A two-component polyurethane composition comprising a polyol component with an average OH functionality greater than 2 and a compound with a single thiol group, combined with a polyisocyanate component containing a polyurethane polymer and a metal catalyst that forms thio complexes, allowing for a long pot life and rapid curing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If high proportions of isocyanates are used to achieve rapid curing and high mechanical strength, then curing speed and strength are improved, but pot life becomes too short for practical use
Solution Approach 1:
The invention divides the isocyanate component into two segments: polymeric polyisocyanates (providing controlled reactivity and long pot life) and monomeric diisocyanates (providing rapid curing and high strength). This segmentation allows each component to fulfill its specific function without the drawbacks of using only one type.
Solution Approach 2:
The invention changes the molecular weight parameter of the isocyanate components, using a combination of high molecular weight polymeric polyisocyanates (≥1000 g/mol) and low molecular weight monomeric diisocyanates (≤300 g/mol). This parameter variation enables control over both pot life and curing speed.
2Strength
If high proportions of isocyanates are used to achieve high mechanical strength, then tensile shear strength is improved, but brittleness increases
Solution Approach 1:
The invention creates a composite polyurethane system combining polymeric polyisocyanates and monomeric diisocyanates in specific proportions (0.1-10 wt% monomeric diisocyanate, 90-99.9 wt% polymeric polyisocyanate). This composite approach achieves high strength while maintaining elasticity by balancing the rigidifying effect of monomeric diisocyanates with the flexible network from polymeric polyisocyanates.
3Object-affected harmful factors
If monomeric diisocyanates are replaced with polyurethane polymers to reduce EHS concerns, then safety and environmental compliance are improved, but achieving long pot life with fast curing becomes difficult
Solution Approach 1:
Instead of completely replacing monomeric diisocyanates, the invention uses a partial amount (0.1-10 wt%) to achieve the desired curing speed and mechanical properties, while the majority (90-99.9 wt%) consists of safer polymeric polyisocyanates. This partial use minimizes EHS concerns while maintaining performance.
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 composition achieves a long pot life of 4 to 7 minutes with rapid curing, developing tensile shear strength of at least 0.1 MPa within 10 to 20 minutes and 2.0 MPa within 30 to 60 minutes, suitable for structural adhesives with excellent mechanical properties.
Implementation Method 1
at least one metal catalyst for the reaction of hydroxyl groups and isocyanate groups that is able to form thio complexes
Implementation Method 2
metal catalyst for the reaction of hydroxyl groups and isocyanate groups that is able to form thio complexes
Implementation Method 3
cure to form a polymeric network
Implementation Method 4
crosslinking and curing
Data Source
AI summary
The present invention relates to a polyurethane composition consisting of a first component A and a second component B, wherein the first component A comprises at least one polyol A1 having an average OH functionality of more than 2 and a number average molecular weight Mn in the range from 250 to 15'000 g/mol; and at least one compound T that has at least one thiol group; and the second component B comprises at least one polyisocyanate I; wherein one of the two components additionally comprises at least one metal catalyst K for the reaction of hydroxyl groups and isocyanate groups that is able to form thio complexes; and the molar ratio of all the thiol groups in the at least one compound T to all metal atoms in the at least one metal catalyst K is between 1:1 and 250:1; characterized in that compound T comprises or consists of a compound having only one thiol group; and polyisocyanate I comprises a polyurethane polymer PU containing isocyanate groups; and component B exhibits a total isocyanate content of between 100 and 400 mmol NCO per kilogram of component B. Such a composition cures very rapidly to form a mechanically excellent mass suitable as structural adhesive or semi-structural elastic adhesive, but at the same time exhibits an adequately long pot life allowing it to be handled comfortably and that can be formulated with a very low isocyanate content, especially a very low content of monomeric diisocyanates.