Polyurethane-Polyurea Dispersion for Aqueous Basecoat Stability
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Solution Overview
Problem
Multi-layer coatings in the automotive industry face issues with storage stability and application properties, particularly in aqueous basecoats containing color and/or effect pigments, due to the formation of air, solvent, and moisture inclusions, leading to pinholes and uneven appearances, and the challenge of maintaining good application properties while increasing the solids content for an improved ecological profile.
Innovation Solution
A pigmented aqueous basecoat containing a polyurethane-polyurea dispersion with specific solvent composition, where the dispersion has polyurethane-polyurea particles with an average size of 40 to 2000 nm and a gel content of at least 50%, and solvents with an HLB value between 5 and 15, selected to enhance storage stability and application properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If the solids content of waterborne basecoats is increased to improve the ecological profile, then the environmental performance is improved, but the storage stability suffers due to pigment settling
Solution Approach 1:
The patent modifies the molecular weight distribution of the polyurethane dispersion, specifically using a weight-average molecular weight (Mw) of 5,000 to 50,000 and a polydispersity index (Mw/Mn) of 1.05 to 2.00. These parameter changes optimize the rheological properties and steric stabilization of the dispersion, allowing high solids content formulations to maintain storage stability without excessive pigment settling
Solution Approach 2:
The patent employs a composite binder system combining polyurethane-polyurea dispersion with specific solvent composition (HLB value 5-15). This composite material approach creates synergistic effects where the polyurethane provides structural integrity and the optimized solvent system enhances pigment wetting and suspension, achieving both high solids content and improved storage stability
2Loss of substance
If the solids content of waterborne basecoats is increased to reduce organic solvent usage, then the ecological profile is improved, but the application properties deteriorate due to increased viscosity and poor flow
Solution Approach 1:
The patent optimizes the polydispersity index (Mw/Mn) to a narrow range of 1.05 to 2.00, which controls the viscosity profile of the dispersion. This parameter optimization ensures that even at high solids content (40-60 wt%), the basecoat maintains appropriate rheological properties for spray application, flow, and leveling without being too thick or too thin
Solution Approach 2:
The patent introduces solvents with specific HLB values (5-15) to create local micro-environments around pigment particles and polymer chains. These solvents provide localized lubrication and reduce interparticle friction, improving flow and application properties in specific regions of the coating while maintaining high overall solids content
3Productivity
If air, solvent, and moisture inclusions are present in multi-layer coatings, then the coating can be applied efficiently, but the visual appearance deteriorates due to pinholes and boils
Solution Approach 1:
The patent incorporates volatile components (solvents with specific HLB values and water) that evaporate during the drying process. This preliminary action allows air and solvent inclusions to escape during application and initial drying, preventing pinhole and boil formation in the final cured coating while maintaining application efficiency
Solution Approach 2:
The polyurethane-polyurea dispersion acts as an intermediary medium that traps and manages air and moisture inclusions during application. The dispersion's optimized molecular structure provides a matrix that allows controlled release of volatiles while preventing coalescence of air bubbles, thereby maintaining both application efficiency and visual appearance
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 achieves excellent storage stability and maintains good application properties, including reduced pinhole formation and improved running stability, while allowing for high solids content and reduced solvent usage, resulting in an ecologically advantageous paint system.
Implementation Method 1
The presence of polymer dispersions as binders influences, among other things, the sedimentation rate depending on the size of the particles from the dispersions, the effect of the solvent on stabilizing those particles
Implementation Method 2
the effect of the solvent on stabilizing those particles, and the influence on viscosity
Implementation Method 3
a specific solvent composition... solvents with an HLB value between 5 and 15, selected to enhance storage stability and application properties
Implementation Method 4
the effect of the solvent on stabilizing those particles, and the influence on viscosity
Implementation Method 5
The level of solids content also influences other rheological properties, such as pronounced shear viscosity
Implementation Method 6
The level of solids content also influences other rheological properties, such as pronounced shear viscosity
Implementation Method 7
The quantities of organic solvents or water, as well as the amount of air introduced during application, are too large for the entire amount to escape from the multi-layer coating during curing without creating defects
Data Source
AI summary
The present invention relates to a pigmented aqueous base paint containing an aqueous polyurethane-polyurea dispersion (PD) comprising polyurethane-polyurea particles which are contained in the dispersion and have an average particle size (volume average) of 40 to 2000 nm and a gel content of at least 50 wt.%. The polyurethane-polyurea particles each contain, in the reacted form, (Z1.1) at least one polyurethane prepolymer containing isocyanate groups and having anionic groups and/or groups which can be converted into anionic groups, and (Z.1.2) at least one polyamine containing two primary amino groups and one or two secondary amino groups, the aqueous base paint containing a special solvent composition. The present invention also relates to the use of base paints containing said dispersion (PD) and to multi-layer paints which were produced by using said base paints.