Polyurethane Allophanate Network Reduces Di-isocyanate Monomer
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Solution Overview
Problem
Current polyurethane systems face challenges due to high residual monomer contents, particularly di-isocyanates, which are classified as potentially carcinogenic, leading to regulatory restrictions and increased costs in reducing monomer concentrations, such as through distillation or viscosity control, without achieving low monomer levels effectively.
Innovation Solution
A method to prepare a reactive polyisocyanate composition with less than 1 wt% monomeric di-isocyanate, utilizing an allophanate-based polyisocyanate intermediate prepolymer and isocyanate reactive compounds, with a specific NCO value and allophanate to urethane group ratio, to achieve a low monomeric di-isocyanate content, suitable for applications in sealants, coatings, and adhesives.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If distillation technique is used to strip off volatile isocyanate monomers, then monomer concentration is reduced, but capital costs and operation costs increase due to extra unit operation
Solution Approach 1:
The invention changes the chemical composition parameters of the polyisocyanate system by incorporating allophanate groups (formed by reacting polyisocyanate with itself at controlled ratios) to transform the system into a self-crosslinking network that inherently traps and reduces free monomer, eliminating the need for distillation while achieving <1 wt% monomer content
Solution Approach 2:
The invention creates a composite polyisocyanate system combining urethane groups (from polyol reaction) and allophanate groups (from self-reaction) in a specific ratio, forming a hybrid structure that provides both low monomer content and self-crosslinking capability without requiring additional processing steps
2Quantity of substance
If NCO/OH ratio is lowered during prepolymer synthesis to reduce monomer content, then monomer concentration decreases, but average Mw increases exponentially causing extremely high viscosities
Solution Approach 1:
The invention changes the reaction pathway by introducing allophanate formation (self-reaction of NCO groups) as a parallel mechanism that consumes excess isocyanate without requiring proportional increases in polyol content, thus reducing monomer while maintaining workable viscosity through network formation rather than simple dilution
3Quantity of substance
If complete tipping of isocyanates with tipping agents is used to eliminate monomer, then isocyanate free materials are obtained, but viscosity increases above 150 Pas making them unsuitable for several PU applications
Solution Approach 1:
The invention extracts the harmful monomer component by transforming it into bound allophanate groups within the polymer network, retaining the beneficial crosslinking functionality while eliminating free isocyanate, achieving monomer-free status without requiring external tipping agents that would increase viscosity
4Quantity of substance
If blocked isocyanates are used to reduce monomer content, then isocyanate is converted into blocked analogue, but deblocking temperatures exceed 100-150°C and release of blocking agent yields EHS issues
Solution Approach 1:
The invention converts the potentially harmful free isocyanate monomer into beneficial allophanate crosslinks within the polymer network, where the same NCO groups that could exist as free monomers are instead utilized to form stable crosslinked structures, eliminating VOC emissions while maintaining curability
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 method effectively reduces monomeric di-isocyanate content to below 0.5 wt% in the final polyisocyanate composition, meeting regulatory standards and maintaining suitable viscosity for application, while avoiding the need for additional processing steps and costly tipping agents.
Implementation Method 1
reacting a polyisocyanate compound with a monool
Implementation Method 2
said composition comprises urethane groups and allophanate groups and wherein the ratio of allophanate groups over urethane groups is between 0.05 and 100
Data Source
AI summary
A urethane group-containing reactive polyisocyanate composition is disclosed which contains not more than 1 wt% of monomeric starting di-isocyanate based on the total weight of said polyisocyanate composition, having an NCO value in the range 0.1-15%, and wherein said composition comprises urethane groups and allophanate groups and wherein the ratio of allophanate groups over urethane groups is between 0.05 and 100.