Moisture-Curing Polyisocyanate Coatings for Elasticity and Drying Speed
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Solution Overview
Problem
Moisture-curing polyurethane coatings based on TDI trimers are brittle and prone to cracking due to high drying speed, while modifications for flexibility result in slower drying and poor light and weather resistance.
Innovation Solution
Formulating polyisocyanate mixtures with TDI isocyanurates and nitrogen-containing polyethers, combined with aliphatic polyisocyanates, to achieve high solids content, rapid drying, elasticity, and improved yellowing resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If TDI trimers with high degree of branching are used for rapid drying, then drying speed is improved, but the coating becomes brittle and loses elasticity
Solution Approach 1:
The patent combines TDI isocyanurate prepolymers (providing rapid drying through high branching) with long-chain polyethers (providing flexibility and elasticity). This composite polymer system allows the coating to dry quickly while maintaining the required elastic properties to prevent cracking on substrates with volume fluctuations.
2Strength
If long-chain polyethers are added to improve flexibility, then elasticity is improved, but drying speed decreases significantly
Solution Approach 1:
The patent carefully controls the molecular weight of the polyether component (500-5000 g/mol) and its proportion in the mixture (5-50% by weight). By optimizing these parameters, the coating achieves sufficient elasticity without excessive softening that would slow down the drying process. The balanced formulation maintains both flexibility and rapid drying characteristics.
3Strength
If polyether content is increased to improve compatibility and flexibility, then elasticity is improved, but light and weather resistance deteriorates due to yellowing
Solution Approach 1:
The patent optimizes the polyether molecular weight range (500-5000 g/mol) and controls the polyether content (5-50% by weight) to achieve the right balance between elasticity and yellowing resistance. Additionally, the use of TDI isocyanurates with controlled isomer composition (80-100% 2,4-TDI and 0-20% 2,6-TDI) helps minimize yellowing while maintaining the required flexibility.
4Reliability
If solids content is increased to >50% by weight for better performance, then durability is improved, but formulation complexity increases
Solution Approach 1:
The patent achieves high solids content (>50% by weight) by optimizing the NCO index (0.8-1.5) and carefully selecting the molecular weights and proportions of the polyether and prepolymer components. This parameter optimization allows the formulation to maintain high durability and performance while managing the complexity of the multi-component system through systematic control of key parameters.
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 provides coatings with high hardness, excellent solvent and chemical resistance, and reduced yellowing, maintaining rapid drying speed comparable to nitrocellulose paints with enhanced durability.
Implementation Method 1
After application, crosslinking takes place under the influence of atmospheric moisture with the formation of urea groups
Data Source
AI summary
Solvent-containing polyisocyanate mixture (I) comprises: (a) tolylene diisocyanate (TDI) component comprising TDI isocyanurate polyisocyanates; (b) aliphatic and/or cycloaliphatic isocyanate component comprising aliphatic and/or cycloaliphatic polyisocyanates; and the reaction product of at least one of components (a) and/or (b) with (c) at least one polyether polyol having a number-average molecular weight of 500-4000 g/mol that contains at least one tertiary nitrogen atom; and (d) optionally at least one polyether polyol that does not contain nitrogen atoms. Solvent-containing polyisocyanate mixture (I) having a solvent content of less than 50 wt. % at a runout viscosity at 23[deg] C of 20 s, an isocyanate groups (NCO) content of 7-15 wt. %, a content of monomeric TDI of less than 0.2 wt. %, and a content of monomeric aliphatic and/or cycloaliphatic isocyanates of less than 0.2 wt. %, where the mixture comprises: (a) TDI component comprising TDI isocyanurate polyisocyanates; (b) aliphatic and/or cycloaliphatic isocyanate component comprising aliphatic and/or cycloaliphatic polyisocyanates; and the reaction product of at least one of components (a) and/or (b) with (c) at least one polyether polyol having a number-average molecular weight of 500-4000 g/mol that contains at least one tertiary nitrogen atom; and (d) optionally at least one polyether polyol that does not contain nitrogen atoms. Independent claims are included for: (1) preparing (I), where the prepolymer mixture of (a) and (b) is prepared by reacting at least one of the two components (a) and/or (b) with (c) and (d) in the presence of organic solvents; (2) a coating comprising (I), a catalyst that accelerates the reaction of free NCO groups with moisture, and one or more auxiliary substances and additives; and (3) a substrate coated with a coating comprising (I).