Multilayer Coating Film Sagging Prevention via Segmented Curing
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Solution Overview
Problem
Existing multilayer coating film formation methods for automotive bodies fail to achieve a high-quality design with excellent luster and smoothness, often resulting in insufficient finished appearance due to sagging and unevenness.
Innovation Solution
A method involving sequential application and curing of solvent-based intermediate paints, an aqueous base paint, an effect pigment dispersion, and a clear paint, using specific coating conditions and components to achieve optimal film thickness and viscosity, ensuring excellent smoothness and luster.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional wet-on-wet process with single baking treatment is used, then the process is simple and efficient, but the coating film exhibits sagging and unevenness resulting in insufficient finished appearance
Solution Approach 1:
The coating process is segmented into multiple sequential stages: applying solvent-based intermediate paint, curing it, then applying aqueous base paint, effect pigment dispersion, and clear paint with separate curing steps. This segmentation allows each layer to be optimized independently, preventing sagging and unevenness while achieving excellent finished appearance quality.
Solution Approach 2:
The solvent-based intermediate paint is applied and cured before applying the aqueous base paint and effect pigment dispersion. This preliminary action creates a stable, smooth foundation that prevents subsequent layers from sagging, enabling excellent finished appearance while maintaining process control.
2Quantity of substance
If the effect coating film has small film thickness to reduce weight and material usage, then material consumption is reduced, but the metallic luster becomes insufficient
Solution Approach 1:
The invention changes the physical and chemical parameters of the effect pigment dispersion, including using specific flake-aluminum pigments with controlled thickness (70-250 nm), adjusting solids content (2-9 mass%), and controlling film thickness (0.5-2.0 μm). These parameter optimizations enable sufficient metallic luster with reduced material consumption compared to conventional thicker coatings.
Solution Approach 2:
The effect pigment dispersion is formulated as a composite material containing flake-aluminum pigment, hydroxy-containing acrylic resin, rheology control agent, and surface-adjusting agent. This composite structure enhances the metallic luster efficiency, allowing thin film thickness (0.5-2.0 μm) to achieve sufficient luster while reducing overall material usage.
3Strength
If the base coating film surface is made non-smooth to improve adhesion and coverage, then coating durability is improved, but the effect coating film reflects the non-smooth surface resulting in insufficient finished appearance
Solution Approach 1:
The invention applies different surface quality requirements to different layers: the solvent-based intermediate paint layer provides adhesion and coverage with appropriate surface texture, while the aqueous base paint and effect pigment dispersion layers are applied over a cured, smooth intermediate surface. This local quality differentiation ensures both adhesion strength and surface smoothness for excellent finished appearance.
Solution Approach 2:
The solvent-based intermediate paint acts as an intermediary layer between the substrate and the aqueous base paint. It provides the necessary adhesion and coverage properties while being cured to create a smooth surface that prevents defect reflection in the effect coating film, thus mediating between adhesion requirements and surface smoothness requirements.
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 method produces a multilayer coating film with excellent finished appearance and luster, reducing sagging and unevenness, thereby enhancing the visual quality and saleability of coated products.
Implementation Method 1
heating the uncured first intermediate coating film to cure the coating film
Implementation Method 2
heating the uncured second intermediate coating film to cure the coating film
Implementation Method 3
heating the uncured base coating film, the uncured effect coating film, and the uncured clear coating film to simultaneously cure the coating films
Data Source
AI summary
The present invention provides a multilayer coating film-forming method that is capable of forming a multilayer coating film with excellent finished appearance and excellent luster. The aqueous base paint (X) is applied by using a rotary-atomization bell-shaped coater under coating conditions of a shaping air pressure of 0.15 to 0.25 MPa and a paint discharge amount of 100 to 300 cm3/min. The viscosity 60 seconds after the application of the aqueous base paint (X), measured at a temperature of 23° C. and a shear rate of 0.1 sec-1, is 90 to 160 Pa·s, the solids content 60 seconds after the application is 20 to 40 mass %, and the film thickness 60 seconds after the application is 17 to 35 μm. The effect pigment dispersion (Y) contains a flake-aluminum pigment (A) with an average thickness of 1 nm or more and less than 70 nm, a flake-aluminum pigment (B) with an average thickness of 70 nm to 250 nm, a hydroxy-containing acrylic resin (C), a rheology control agent (D), a surface-adjusting agent (E), and water, the effect pigment dispersion (Y) having a solids content of 2 to 9 mass %. The effect coating film after curing has a film thickness of 0.5 to 2.0 μm.