TDI Polyisocyanate Mixture for Low Viscosity High Solids Coatings
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Solution Overview
Problem
Polyisocyanates based on tolylene diisocyanate (TDI) face challenges with high viscosity, leading to difficult processing and high solvent emissions, as well as a high content of monomeric TDI, which is toxicologically concerning and limits their usability in surface coatings and adhesives.
Innovation Solution
A polyisocyanate mixture comprising polyisocyanurate and polyurethane both based on TDI, with a high content of isocyanate groups and low viscosity, achieved by controlling the reaction conditions and blending with polyurethane resins to achieve a solids content of ≥ 51 to ≤ 90% and a monomeric TDI content of ≤ 0.9%, while maintaining low viscosity and reducing volatile organic solvent emissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If polyisocyanurate is prepared by cyclotrimerization of TDI, then isocyanate groups are formed for crosslinking, but the resin becomes very highly viscous making processing difficult
Solution Approach 1:
The patent combines polyisocyanurate (providing crosslinking capability) with polyurethane resin (providing low viscosity and good processability) in a mixture where the polyisocyanurate content is 10-90% by weight. This merging allows the formulation to achieve both high crosslinking performance and easy processing without requiring large amounts of organic solvents.
2Object-generated harmful factors
If high solids content is achieved to reduce solvent emissions, then VOC emissions are reduced, but viscosity increases making application difficult
Solution Approach 1:
The patent creates a composite material system combining polyisocyanurate and polyurethane resin in specific ratios (polyisocyanurate 10-90% by weight). This composite formulation achieves high solids content (reducing VOC emissions) while the polyurethane component maintains low viscosity for good application behavior, eliminating the need for large amounts of organic solvents.
3Productivity
If polyisocyanate has high functionality for rapid crosslinking, then process efficiency increases, but the content of monomeric TDI increases which is toxicologically concerning
Solution Approach 1:
The patent optimizes the molecular weight and functional group content parameters of the polyisocyanurate component, controlling it to contain 15-40% by weight isocyanate groups. This parameter optimization ensures rapid crosslinking (high productivity) while the polyurethane component keeps the overall monomeric TDI content low (≤5% by weight), reducing toxicological concerns.
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 solution results in a polyisocyanate mixture with increased isocyanate groups, reduced viscosity, and lower solvent emissions, enhancing processing efficiency and occupational hygiene, allowing for broader application in surface coatings and adhesives with improved crosslinking properties.
Implementation Method 1
Their purpose is to effect chemical crosslinking of isocyanate-reactive components, e.g. polyols, and curing to give a chemicals-resistant and mechanically strong film
Implementation Method 2
Isocyanurates of TDI are prepared by cyclotrimerization using various catalysts
Data Source
AI summary
The invention relates to a polyisocyanate mixture comprising at least one polyisocyanurate which is based on tolylene diisocyanate and has isocyanate groups and at least one polyurethane which is based on tolylene diisocyanate and has isocyanate groups, wherein the polyisocyanate mixture has a) a solids content of from ≥ 51 to ≤ 90% by weight, based on the total weight of the polyisocyanate mixture and b) a content of monomeric tolylene diisocyanate of ≤ 0.9% by weight, based on the total weight of the polyisocyanate mixture, and the polyisocyanurate which is based on tolylene diisocyanate and has isocyanate groups has a polydispersity D of from ≥ 1 to ≤ 1.5, based on the total weight of the polyisocyanurate which is based on tolylene diisocyanate and has isocyanate groups, where the polydispersity D is the ratio of weight average and number average molecular weight of the polyisocyanurate and the weight average and number average molecular weight is in each case determined by means of gel permeation chromatography using a polystyrene standard and tetrahydrofuran as eluent in accordance with DIN 55672-1:2016-03.