Multi-Layer Coating Joint Curing Stability
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Solution Overview
Problem
The existing multi-layer coating processes for metallic substrates often result in pinholes and aesthetic defects due to the omission of separate curing steps, particularly when using aqueous coating agents, which can lead to air, solvent, and moisture inclusions, and require thicker basecoat layers, increasing the risk of needle sticks and compromising ecological compatibility.
Innovation Solution
A method for producing multi-layer coatings where a hardened electrophoretic paint layer is applied on a metallic substrate, followed by directly successive aqueous basecoat layers and a clearcoat layer, with joint curing of the basecoat and clearcoat layers, utilizing a copolymer dispersion and a linear hydroxy-functional reaction product to enhance stability and reduce defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If separate curing steps are omitted to simplify the manufacturing process, then productivity is improved, but manufacturing precision deteriorates due to pinholes and aesthetic defects
Solution Approach 1:
The patent combines the curing of basecoat and clearcoat layers into a single joint curing step. The basecoat and clearcoat are cured together in one operation rather than separately, which simplifies the manufacturing process while maintaining aesthetic quality through the specific formulation of the aqueous dispersion containing copolymers with controlled molecular weight and functional groups that prevent pinhole formation during the combined curing process.
Solution Approach 2:
The patent changes the chemical parameters of the coating system by using an aqueous dispersion containing specific copolymers (with number-average molecular weights of 5,000-50,000 and specific functional groups) instead of conventional organic solvents. This parameter change allows the coating to maintain stability and prevent pinhole formation during joint curing, resolving the contradiction between process simplification and aesthetic quality.
2Object-affected harmful factors
If aqueous coating agents are used to meet ecological requirements, then environmental compatibility is improved, but reliability deteriorates due to air, solvent, and moisture inclusions forming pinholes
Solution Approach 1:
The patent uses a composite aqueous dispersion system containing copolymers with specific molecular weight ranges (5,000-50,000 number-average) and specific functional groups. This composite material structure provides both ecological compatibility (being water-based) and reliability (preventing pinhole formation) by controlling the rheological and curing properties of the coating system.
Solution Approach 2:
The patent applies local quality control by specifying particular molecular weight ranges and functional group compositions for the copolymers in the aqueous dispersion. These localized chemical property specifications ensure that the coating maintains stability and prevents pinhole formation in critical areas during the curing process, while still being environmentally friendly.
3Manufacturing precision
If basecoat layer thickness is increased to maintain aesthetic properties without separate curing, then manufacturing precision is improved, but device complexity increases due to higher risk of needle sticks
Solution Approach 1:
The patent changes the physical and chemical parameters of the basecoat formulation by using aqueous dispersions with specific copolymer molecular weights (5,000-50,000 number-average) and functional groups. This allows the use of thicker basecoat layers to maintain aesthetic quality without increasing the risk of needle sticks, as the controlled polymer structure prevents defect formation during joint curing with the clearcoat layer.
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
This method allows for the production of multi-layer paint systems with excellent stability against pinholes, enabling higher layer thicknesses without aesthetic compromise and meeting ecological requirements by eliminating separate curing steps and using aqueous coating agents.
Implementation Method 1
an electrophoretic paint, in particular a cathodic electrophoretic paint, is first applied or deposited electrophoretically on the metallic substrate
Implementation Method 2
the basecoat (b.2.1) or at least one of the basecoats (b.2.2.x) comprises at least one aqueous dispersion containing at least one copolymer (MP), wherein the copolymer (MP) can be produced, by (i) presenting an aqueous dispersion of at least one polyurethane, and then (ii) polymerizing a mixture of olefinically unsaturated monomers in the presence of the polyurethane
Implementation Method 3
at least one linear hydroxy-functional reaction product (R) with an acid number of less than 20 mg KOH/g, the production of which involves at least one compound (v) containing two functional groups (v.1)
Implementation Method 4
the one or more basecoat layers and the clearcoat layer are cured together
Data Source
Figure 1~3
AI summary
The present invention relates to a method for producing a multi-layer lacquer finish on a metal substrate, wherein a base lacquer coat or a plurality of directly consecutive base lacquer coats are produced directly on a metallic substrate coated with a hardened electrophoretic dip coat, a clear lacquer coat is produced directly on the one or the upper of the plurality of said base lacquer coats, and the one or the plurality of base lacquer coats and the clear lacquer coat are subsequently hardened together. The method is characterized in that at least one base lacquer employed for producing the base lacquer coats comprises at least one aqueous dispersion which contains at least one copolymer (MP). The copolymer (MP) can be produced by providing an aqueous dispersion of at least one polyurethane followed by polymerization of a mixture of olefinically unsaturated monomers in the presence of the polymer produced in (i), a water-soluble initiator being employed, and the dosing of the olefinically unsaturated monomer being performed such that in the reaction solution a concentration of 6.0 wt.% relative to the total amount of the olefinically unsaturated monomers employed for polymerization is not exceeded during the entire reaction time and the mixture of olefinically unsaturated monomers containing at least one olefinically polyunsaturated monomer and at least one linear hydroxy-functional reaction product (R) having an acid number of less than 20 mg KOH/g. During the production of said reaction product at least one compound (v) is employed which comprises two functional groups (v.1) and, arranged between the functional groups, an aliphatic or araliphatic hydrocarbon group (v.2) having 12 to 70 hydrocarbon atoms.