Aqueous Polyurethane-Polyurea Dispersion for High-Solids Basecoats
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Solution Overview
Problem
Multi-layer coatings in the automotive industry face issues with air, solvent, and moisture inclusions leading to pinholes, and struggle to achieve high solids content while maintaining acceptable storage stability and rheological properties, particularly in aqueous basecoats containing color and/or effect pigments.
Innovation Solution
An aqueous polyurethane-polyurea dispersion with polyurethane-polyurea particles of 40 to 2000 nm in size and a gel content of at least 50%, produced through a specific three-step process, is used to create a pigmented aqueous basecoat that enhances application properties and storage stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If the solids content of aqueous basecoats is increased to improve ecological profile, then the proportion of organic solvents is reduced, but storage stability and rheological properties deteriorate
Solution Approach 1:
The patent changes the chemical composition parameters of the dispersion system by introducing a specific polyurethane-polyurea copolymer with defined molecular weight (5,000-50,000 g/mol) and functional group ratios. This parameter optimization allows achieving high solids content (30-70% by weight) while maintaining storage stability through the balanced amine-isocyanate stoichiometry (0.9:1.1 ratio) and controlled gel content (10-60%)
Solution Approach 2:
The patent creates a composite aqueous dispersion system combining polyurethane segments (from diisocyanate and polyol) with polyurea segments (from polyamine extension). This composite structure integrates the hydrophobicity and mechanical strength of polyurethane with the hydrogen-bonding capability and water solubility of polyurea, enabling high solids content formulations to maintain stability without excessive organic solvents
2Ease of operation
If inorganic layered silicates are used to achieve structural viscosity, then pseudoplastic properties are improved, but solids content needs to be reduced
Solution Approach 1:
The patent introduces a small-molecule polyamine (3-10% by weight based on total amine content) as an intermediary that bridges the polyurethane prepolymer and water phase. This polyamine intermediary forms polyurea linkages that create physical crosslinks and hydrogen-bonding networks, generating structural viscosity and pseudoplastic behavior without requiring inorganic silicate fillers, thus allowing high solids content to be maintained
3Ease of manufacture
If air, solvent and moisture inclusions are present in multi-layer coatings, then application is simplified, but pinholes and visual defects occur
Solution Approach 1:
The patent applies preliminary action by incorporating a blowing agent (5-50 parts by weight per 100 parts polymer) into the polyurethane-polyurea dispersion before application. This pre-incorporated gas phase creates controlled cellular structures that facilitate the escape of air, solvent, and moisture inclusions during curing, preventing pinhole formation and surface defects while maintaining application ease
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 dispersion and basecoat achieve excellent optical and mechanical properties, such as needle stitch behavior and stone chip resistance, while allowing for high solids content and improved ecological production, maintaining good storage stability and rheological behavior.
Implementation Method 1
at least one polyurethane prepolymer containing isocyanate groups (Z.1.1) and (Z.1.2) at least one polyamine containing two primary amino groups and one or two secondary amino groups
Implementation Method 2
a gel content of at least 50%
Implementation Method 3
pronounced structural viscosity. The latter is the case when, on the one hand, the coating agent has such a low viscosity during the application process (usually spray application) with the high shear that is given that it can be atomized reasonably
Data Source
AI summary
The invention relates to an aqueous polyurethane polyurea dispersion (PD) comprising polyurethane polyurea particles contained in said dispersion and having an average particle size of between 40 - 2000 nm and a gel content of at least 50%. The polyurethane polyurea particles contain, in the converted form, (Z1.1) at least one polyurethane-prepolymer containing isocyanate groups, having anionic groups and/or groups which can be converted into anionic groups and (Z.1.2) at least one polyamine containing at least two masked primary amino groups and one or more secondary amino groups, the dispersion (PD) containing at least 90 wt.% of polyurethane polyurea particles and water. The invention also relates to base paints containing said dispersion (PD) and to multi-layer paints which can be obtained by using said base paint.