Moisture-Curing Prepolymers for Elastic Coatings
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Solution Overview
Problem
Moisture-curing polyurethane coatings based on TDI isocyanurates dry rapidly but become brittle, lacking elasticity and often crack under temperature fluctuations, while flexibilizing agents like polyethers slow drying and cause compatibility issues, leading to cloudy or unstable products.
Innovation Solution
Formulations containing NCO-containing prepolymers made from TDI isocyanurate polyisocyanates and diphenylmethane diisocyanates, using a polyetherdiol with ethylene oxide blocks, which are prepared in organic solvents to achieve a balance of rapid drying and elasticity, with specific NCO, solids, and monomeric content.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If TDI isocyanurate polyisocyanates are used for rapid drying, then drying rate is improved, but elasticity deteriorates and brittleness increases
Solution Approach 1:
The patent combines TDI isocyanurate polyisocyanates (for rapid drying) with diphenylmethane diisocyanates and specific polyetherdiols (for elasticity) to create a hybrid polyurethane prepolymer system that achieves both rapid drying and maintained elasticity, resolving the contradiction between drying rate and elasticity
Solution Approach 2:
The invention creates a composite polyurethane prepolymer system incorporating multiple isocyanate types (TDI isocyanurate and diphenylmethane diisocyanate) and specific polyetherdiols with controlled molecular weights and ethylene oxide content, forming a composite material that exhibits both rapid drying characteristics and elastic properties
2Strength
If polyethers are added for flexibilization, then elasticity is improved, but drying rate deteriorates
Solution Approach 1:
The patent specifies precise parameter ranges for polyetherdiols (molecular weight 3000-4500 g/mol, ethylene oxide content 2-18% by weight) to optimize the balance between elasticity and drying rate, ensuring that flexibilization does not excessively retard drying while maintaining required elastic properties
3Strength
If long-chain polyethers are used for flexibilization, then elasticity is improved, but storage stability deteriorates and cloudiness occurs
Solution Approach 1:
The invention constrains the molecular weight of polyetherdiols to 3000-4500 g/mol and ethylene oxide content to 2-18% by weight, preventing the formation of cloudy or unstable products while maintaining adequate elasticity, thus resolving the contradiction between elasticity and storage stability
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 enables the production of coatings that dry quickly like nitrocellulose lacquers while maintaining the elasticity and resistance of polyurethane coatings, with improved storage stability and resistance to cracking.
Implementation Method 1
prepolymers are prepared in the presence of organic solvents by reacting at least one of components A) and B) with C) a polyetherdiol
Implementation Method 2
Following application, under the influence of atmospheric moisture, crosslinking takes place with formation of urea groups
Implementation Method 3
crosslinking takes place with formation of urea groups
Data Source
AI summary
Solvent-containing formulations including NCO-containing prepolymers based on TDI isocyanurate polyisocyanates and diphenylmethane diisocyanates where some prepolymers are prepared using a polyetherdiol containing ethylene oxide blocks and having an ethylene oxide content of from 2 to 18% by weight, based on all the alkylene oxide units. The formulation have an NCO content of 1% to 7% by weight, a solids content of 20% to 70% by weight, a monomeric TDI content of less than 0.2% by weight and a monomeric methylenediphenyl diisocyanate content of less than 2% by weight. The solvent-containing formulations can be prepared in organic solvents by reacting at least one of A) a TDI component comprising TDI isocyanurate polyisocyanates and B) an MDI component comprising diphenylmethane diisocyanates with C) a polyetherdiol. The solvent-containing formulations can be used in moisture-curing coating compositions, adhesive bonds and/or seals with substrates.