Aqueous Coating Composition Preventing Mixed Layers
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Solution Overview
Problem
Existing aqueous coating compositions used in 3-coat 1-bake and 2-coat 1-bake processes for forming coating films on automobile bodies often result in insufficient water resistance, smoothness, and distinctness of image due to the use of water-soluble or water-dispersible resins, and the formation of mixed layers between coating layers.
Innovation Solution
An aqueous coating composition comprising acrylic urethane resin composite particles, a hydroxy-containing polyester or acrylic resin, and a blocked polyisocyanate compound, which are applied in a specific sequence to inhibit the formation of mixed layers and enhance the properties of the multilayer coating film, including smoothness, distinctness, water resistance, and chipping resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If water-soluble or water-dispersible resins are used in aqueous coating compositions, then environmental pollution is reduced and energy consumption is lowered, but water resistance of the coating film becomes insufficient
Solution Approach 1:
The patent uses composite resin particles comprising both hydrophilic resin (for water dispersibility and environmental compatibility) and hydrophobic resin (for water resistance). This composite structure allows the coating to maintain both environmental friendliness and adequate water resistance performance.
2Object-affected harmful factors
If aqueous intermediate coating composition and aqueous base coating composition are applied in sequence, then organic solvent volatilization is reduced, but mixed layer formation occurs between layers resulting in insufficient smoothness and distinctness of image
Solution Approach 1:
The patent controls the neutralization value parameter of the aqueous base coating composition to be higher than that of the aqueous intermediate coating composition. This parameter difference creates interfacial tension that prevents mixed layer formation, maintaining layer distinctness and surface smoothness while using aqueous systems.
3Use of energy by stationary object
If multiple coating layers are applied in a 3-coat 1-bake or 2-coat 1-bake process, then energy consumption is reduced by eliminating one bake step, but mixed layer formation between aqueous coating layers reduces coating quality
Solution Approach 1:
The patent adjusts the neutralization value parameter between successive aqueous coating layers to prevent mixing. The base coating composition has a higher neutralization value than the intermediate coating, creating sufficient interfacial tension to maintain layer separation during the reduced bake process, thereby preserving coating quality while reducing energy consumption.
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 proposed coating composition achieves excellent smoothness, distinctness of image, water resistance, and chipping resistance by preventing the formation of mixed layers and utilizing the synergistic effects of the resin components, resulting in a high-quality multilayer coating film with improved wash-off properties.
Implementation Method 1
An aqueous coating composition comprising acrylic urethane resin composite particles, a hydroxy-containing polyester or acrylic resin, and a blocked polyisocyanate compound
Implementation Method 2
curing by heating
Data Source
AI summary
The present invention provides an aqueous coating composition for use as an aqueous first colored coating composition in a multilayer coating-forming method, the coating composition containing an aqueous film-forming resin (A), a crosslinking agent (B), and acrylic urethane resin composite particles (C). The acrylic resin of the acrylic urethane resin composite particles (C) is obtained by using, as constituent monomers, 30 to 80 mass % of a polymerizable unsaturated monomer (c-1-1) having one polymerizable unsaturated group per molecule and having a C4-22 alkyl group, 1 to 20 mass % of a polymerizable unsaturated monomer (c-2) having two or more polymerizable unsaturated groups per molecule, and 0 to 69 mass % of a polymerizable unsaturated monomer (c-1-2) having one polymerizable unsaturated group per molecule and being other than the polymerizable unsaturated monomer (c-1-1).