Low-Solvent Polyisocyanate via Partial Trimerization
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Solution Overview
Problem
Current polyisocyanate products with TDI-based isocyanurate groups have high solvent content, exceeding VOC limits set by EU Directive 2004/42/EC, and reducing solvent content through existing methods either compromises reactivity or increases monomer residues, posing occupational health risks.
Innovation Solution
A process involving trimerization of toluene diisocyanate in the absence of solvent, with controlled conversion and catalysts, followed by distillation to achieve a polyisocyanate with low VOC solvent content, high isocyanate-reactive groups, and suitable viscosity for two-pack paints.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the reaction is driven to high conversions to reduce free monomer content, then occupational health and safety is improved, but the mean molecular weight increases and viscosity becomes too high for practical applications
Solution Approach 1:
The patent applies partial action by terminating the trimerization reaction at low conversions (10-60%) rather than driving it to completion. This allows obtaining a polyisocyanate product with mean molecular weight between 500-1500 amu and acceptable viscosity, while the subsequent distillation step removes the small amount of excess monomer to meet safety requirements (<1% TDI monomer residue).
Solution Approach 2:
The patent changes the conversion parameter from high (conventional method) to low (10-60% in this invention), which fundamentally alters the molecular weight distribution and viscosity characteristics of the product. This parameter change enables the use of inexpensive separation techniques like distillation while maintaining product performance.
2Productivity
If long-chain alcohol compounds are used to reduce viscosity and increase dry residue, then application properties are improved, but isocyanate-reactive group content decreases and reactivity is reduced
Solution Approach 1:
The patent extracts the harmful excess monomer through distillation rather than using long-chain alcohols to mask viscosity issues. This extraction approach maintains high isocyanate-reactive group content (>14% w/w) and reactivity, while achieving acceptable viscosity through controlled low-conversion synthesis.
3Object-affected harmful factors
If conventional trimerization methods are used to obtain low monomer content products, then safety is improved, but solvent content exceeds VOC regulatory limits
Solution Approach 1:
The patent changes the conversion parameter to low values (10-60%), which fundamentally alters the product composition to have lower molecular weight and reduced solvent requirements. Combined with distillation of excess monomer, this achieves both safety (<1% monomer) and environmental compliance (<40% VOC solvent content).
Solution Approach 2:
By applying partial action (low conversion termination), the patent avoids the need for high solvent content that would be required in conventional high-conversion methods to manage viscosity and monomer removal, thus achieving both safety and low VOC content.
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 process results in a polyisocyanate with under 40% VOC solvent content, low free monomer content, and high isocyanate-reactive groups, enabling the formulation of paints with improved reactivity and safety while meeting regulatory VOC limits.
Implementation Method 1
trimerisation of TDI in the absence of solvent, and in the presence of a catalyst and an alkanol (C6-C10)
Implementation Method 2
removal of unreacted isocyanate monomer by distillation
Data Source
AI summary
Disclosed is a polyisocyanate obtained by curing toluene diisocyanate, characterised by: - dry residue exceeding 60%, and preferably between 60 and 80% by weight; - viscosity between 500 and 2000 mPas; - a toluene diisocyanate monomer content of under 1% by weight; - a mean molecular weight of under 1500 amu; an isocyanate-reactive group content exceeding 10% by weight.