Aqueous Polyurethane Coating with Silane Crosslinking for Scratch Resistance
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Aqueous polyurethane coating agents face challenges with storage stability due to silane content, leading to gelling issues, which limits scratch resistance and processing time, while also requiring reduction in solvent usage for ecological and economic reasons.
Innovation Solution
Formulating coating compositions with hydroxyl group-containing compounds, isocyanate group-containing compounds with hydrolyzable silane groups, and a catalyst for crosslinking, optimizing the proportion of silane groups and isocyanate conversion to achieve high scratch resistance and chemical resistance, particularly to caustic soda, with improved storage stability and processing time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If silane content is increased to improve scratch resistance, then storage stability deteriorates due to gelling
Solution Approach 1:
The patent extracts the problematic silane groups from the polyisocyanate component and places them in a separate crosslinking agent component. This separation allows the polyisocyanate to remain stable during storage while still providing the desired scratch resistance through controlled crosslinking later. The silane-containing crosslinking agent is kept distinct until application, preventing premature gelling.
Solution Approach 2:
The patent performs preliminary reaction of isocyanate groups with silane groups during the formulation stage to create a pre-reacted polyisocyanate compound with reduced free isocyanate content and controlled silane functionality. This preliminary action stabilizes the system during storage while maintaining the capability for subsequent crosslinking to achieve high scratch resistance.
2Stability of the object's composition
If silane content is limited to improve storage stability, then scratch resistance deteriorates
Solution Approach 1:
The patent introduces a catalyst as an intermediary that mediates between the stable storage state and the high-performance cured state. The catalyst remains inactive during storage, maintaining stability, but activates the crosslinking reaction after application to achieve high scratch resistance. This intermediary enables the system to transition from a stable precursor state to a high-performance crosslinked state.
3Object-affected harmful factors
If solvent proportion is reduced for ecological reasons, then processing time and application characteristics worsen
Solution Approach 1:
The patent changes the chemical parameters of the coating formulation by using water-based polyisocyanate compounds with specific molecular weights and functionality distributions. This parameter change allows the system to maintain adequate processing time and application characteristics with reduced organic solvent content, meeting ecological requirements while preserving workability.
4Reliability
If isocyanate conversion with silane groups is increased to improve crosslinking, then storage stability worsens due to premature reaction
Solution Approach 1:
The patent segments the coating system into distinct functional components: a polyisocyanate compound with partially reacted silane groups and a separate crosslinking agent. This segmentation controls the timing and extent of crosslinking reactions, allowing high crosslinking performance in the cured coating while maintaining storage stability of the individual components before mixing.
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 coating compositions provide high scratch resistance, excellent chemical resistance, and prolonged processing time, suitable for automotive series painting and refinishing, with enhanced surface quality and reduced ecological impact.
Implementation Method 1
at least one catalyst (C) for the crosslinking of silane groups
Implementation Method 2
the proportion of isocyanate groups converted into the structural units (I) and (II) in the compound (B) is between 10 and 60 mol%
Implementation Method 3
compound (B) with free and/or blocked isocyanate groups and with hydrolyzable silane groups
Data Source
AI summary
The invention relates to aqueous coating materials comprising at least one hydroxyl-containing compound (A), at least one compound (B) having isocyanate groups and also having hydrolysable silane groups, and at least one catalyst (C), characterized in that the compound (B) has up to less than 90 mol% of at least one structural unit (I) -N(X-SiR''x(OR')3-x)n(X'-SiR''y(OR')3-y)m (I) where R' = hydrogen, alkyl or cycloalkyl, X, X' = linear and/or branched alkylene or cycloalkylene radical having 1 to 20 carbon atoms, R'' = alkyl, cycloalkyl, aryl, or aralkyl, n = 0 to 2, m = 0 to 2, m+n = 2, and also x, y = 0 to 2, and more than 10 to 90 mol% of at least one structural unit (II) -Z-(X-SiR''x(OR')3-x) (II), where Z = -NH-, -NR-, -O-, -S-, with R = alkyl, cycloalkyl, aryl or aralkyl, and x, X, R' and R'' have the definition indicated for formula (I). Additionally provided by the present invention are multi-stage coating methods using these coating materials, and also the use of the coating materials as clearcoat material and application of the coating method for automotive refinishing and/or for the coating of plastics substrates.