Aqueous Polycarboxylic Acid Coating Leveling and Stability
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Solution Overview
Problem
Existing aqueous coating compositions for multicoat paint systems face challenges with polyamides and metal silicates, leading to issues like pinholes, poor leveling, and storage stability, especially when used in the 'wet-on-wet' method, which affects the quality and appearance of automotive finishes.
Innovation Solution
An aqueous coating composition comprising anionically stabilized binder, color pigment, and polycarboxylic acid, without effect pigments, which uses the polycarboxylic acid as an associative thickener to achieve excellent leveling and storage stability, and enhances the flop effect of metallic coatings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If polyamides and metal silicates are used as rheological assistants, then leveling properties are improved, but pinholes and storage stability deteriorate
Solution Approach 1:
The patent changes the chemical composition parameters by replacing polyamides and metal silicates with carboxymethyl cellulose (CMC) as the rheological assistant. This parameter substitution resolves the contradiction by achieving effective leveling (29) without the pinhole formation and storage stability issues (27) associated with the previous additives.
Solution Approach 2:
The patent employs carboxymethyl cellulose, a water-soluble, biodegradable polymer, replacing the more complex polyamide and metal silicate systems. This simpler, shorter-lived additive achieves the rheological function without the long-term stability problems of the previous system.
2Manufacturing precision
If metal silicates are used as rheological assistants, then leveling is improved, but interactions with other formulation constituents increase
Solution Approach 1:
The patent extracts metal silicates from the formulation entirely, removing the source of complex interactions with dispersing additives and binders. Carboxymethyl cellulose is introduced as a simpler alternative that provides leveling (29) without the problematic interactions (36) of metal silicates.
3Device complexity
If high dilution is used to minimize interactions, then interaction strength is reduced, but shear stability and circulation line stability deteriorate
Solution Approach 1:
The patent uses carboxymethyl cellulose, a simple water-soluble polymer, that provides adequate rheological control at moderate concentrations without requiring high dilution. This eliminates the need to trade off interaction strength (36) against shear stability (14).
Solution Approach 2:
The patent changes the concentration parameter of the rheological assistant to an optimal level for carboxymethyl cellulose, achieving both minimal interactions (36) and adequate shear stability (14) without the high dilution required by metal silicate systems.
4Ease of manufacture
If aqueous basecoat compositions are used for economic and environmental reasons, then processing by wet-on-wet method becomes feasible, but pinholes and visual appearance defects increase
Solution Approach 1:
The patent uses carboxymethyl cellulose, a simple, inexpensive, water-soluble polymer, as the rheological assistant in the aqueous basecoat. This additive enables wet-on-wet processing (32) without causing pinholes or appearance defects (29), unlike previous aqueous systems.
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 improved leveling, storage stability, and increased flop effect in metallic coatings applied 'wet-on-wet', while eliminating the need for polyamides and metal silicates, resulting in high-quality, visually appealing multicoat paint systems.
Implementation Method 1
uses the polycarboxylic acid as an associative thickener to achieve excellent leveling
Implementation Method 2
at least one anionically stabilized binder B
Data Source
AI summary
Disclosed herein is an aqueous coating composition including an anionically stabilized binder, a color pigment, a polycarboxylic acid, and optionally a solvent. Further disclosed is a method for producing an aqueous coating composition by adding a solution of polycarboxylic acid in a solvent to a coating composition including an anionically stabilized binder and color pigment. Additionally disclosed is a method for producing a multicoat paint system by producing a basecoat layer or at least two directly consecutive basecoat layers directly on a substrate optionally coated with a first coating layer, producing a clearcoat layer directly on the basecoat layer or the topmost basecoat layer, and jointly curing the basecoat layer(s) and the clearcoat layer. At least one of the basecoat materials includes the aqueous coating composition disclosed herein and/or an aqueous coating prepared by the disclosed method. A multicoat paint system obtainable by the method is additionally disclosed.