Multilayer Coating Film 3-Coat 1-Bake Process
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Solution Overview
Problem
The 3-coat 1-bake process using aqueous coating compositions results in multilayer coating films with insufficient smoothness and distinctness of image due to the formation of a mixed layer from the intermediate and base coating compositions, and the method disclosed in Patent Literature 2 is difficult to apply as it uses a nonaqueous dispersion as a viscosity-controlling agent.
Innovation Solution
A method involving a 3-coat 1-bake process using an aqueous first colored coating composition with a hydroxy-containing polyester resin and an aqueous second colored coating composition containing a specific copolymer and film-forming resin, applied sequentially with a clear coating composition, to form a multilayer coating film with excellent smoothness, distinctness of image, flip-flop property, and water resistance, while suppressing metallic mottling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a 3-coat 1-bake process using aqueous intermediate coating composition and aqueous base coating composition is used, then energy consumption is reduced and environmental pollution is minimized, but the coating film has insufficient smoothness and distinctness of image due to formation of a mixed layer
Solution Approach 1:
The patent applies local quality by giving different properties to different layers: the intermediate coating layer uses a water-based composition with specific resin properties to prevent mixing, while the base coating layer uses an organic solvent-based composition for excellent smoothness and image distinctness. This localized differentiation allows each layer to optimize its function without compromising the other.
Solution Approach 2:
The patent employs composite materials by combining water-based and organic solvent-based coating compositions in a multi-layer structure. The intermediate layer uses water-based acrylic resin or urethane resin with specific molecular weights and functional groups, while the base layer uses organic solvent-based polyester resin or acrylic resin, creating a composite coating system that leverages the advantages of both composition types.
2Reliability
If an aqueous intermediate coating composition and aqueous base coating composition are used in a 3-coat 1-bake process, then water resistance and environmental friendliness are improved, but metallic mottling occurs and surface smoothness deteriorates
Solution Approach 1:
The patent applies local quality by assigning different resin systems to different layers: the intermediate layer uses water-based acrylic resin or urethane resin with specific functional groups for water resistance, while the base layer uses organic solvent-based polyester or acrylic resin for superior surface smoothness and metallic mottling suppression.
Solution Approach 2:
The patent employs composite materials by creating a multi-layer coating system where the intermediate layer is water-based and the base layer is organic solvent-based. This composite structure allows the intermediate layer to provide water resistance while the base layer delivers excellent surface quality and prevents metallic mottling.
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 achieves a multilayer coating film with enhanced smoothness and distinctness of image, along with improved water resistance and reduced metallic mottling, by using the specified aqueous coating compositions and their respective resins in the 3-coat 1-bake process.
Implementation Method 1
curing by baking
Implementation Method 2
simultaneously curing by baking the intermediate coating film, base coating film, and clear coating film
Data Source
AI summary
The present invention provides a method for forming a multilayer coating film, the method comprising (1) coating on a substrate an aqueous first colored coating composition containing a pigment and a hydroxy-containing polyester resin-containing film-forming resin having an acid value of 30 mg KOH/g or less; (2) coating an aqueous second colored coating composition containing a film-forming resin and a copolymer obtained by copolymerization of monomer components containing a polymerizable unsaturated monomer having a hydrophilic group, and a macromonomer having a polymerizable unsaturated group and a backbone having a number average molecular weight of 1,000 to 10,000, obtained by polymerization of a monomer component having 5 to 100 mass % of a polymerizable unsaturated monomer having a C4-24 alkyl group; (3) coating a clear coating composition; and (4) simultaneously curing the three coating films formed in steps (1) to (3).