Multi-layer coating joint curing aqueous polyurethane-polyurea
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Solution Overview
Problem
The existing multi-layer coating processes for metallic substrates often require a separate curing step for the electrophoretic coating layer, which can lead to pinholes, needle sticks, and inadequate aesthetic and mechanical properties, particularly when trying to reduce layer thickness or eliminate the filler layer.
Innovation Solution
A method involving the production of a multi-layer coating where the basecoat layer is not separately cured but rather hardened jointly with the clearcoat layer, using an aqueous polyurethane-polyurea dispersion with specific particle size and gel content, allowing for variable layer thicknesses and improved adhesion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a separate curing step is performed for the basecoat layer, then adhesion and mechanical properties are improved, but production time and process complexity increase
Solution Approach 1:
The patent combines the curing of the basecoat layer and clearcoat layer into a single simultaneous curing step. The basecoat contains reactive functional groups that crosslink during curing, and the clearcoat is applied before the basecoat fully cures, allowing both layers to cure together in one process step, thereby eliminating the need for separate curing operations while maintaining adhesion and mechanical properties
Solution Approach 2:
The clearcoat is applied to the basecoat layer before the basecoat curing is complete, creating a wet-on-wet or semi-cured state. This preliminary application allows the clearcoat to bond to the basecoat during the subsequent curing process, ensuring good adhesion without requiring a separate curing step for the basecoat
2Manufacturing precision
If the basecoat layer thickness is increased to improve coverage and aesthetic properties, then visual quality is improved, but pinhole formation and curing defects increase
Solution Approach 1:
The patent modifies the chemical composition parameters of the basecoat by incorporating reactive functional groups (isocyanate, hydroxyl, carboxyl, or amino groups) that enable crosslinking during curing. This parameter change allows the basecoat to cure properly even at increased thicknesses, preventing pinhole formation while maintaining improved coverage and aesthetic properties
Solution Approach 2:
The patent creates a composite coating system where the basecoat and clearcoat are chemically integrated through crosslinking reactions. The basecoat contains reactive functional groups that form a crosslinked network during curing, and the clearcoat participates in this network formation, creating a unified composite structure that eliminates pinholes even at higher basecoat thicknesses
3Device complexity
If the filler layer is eliminated or thickness reduced to simplify the process, then manufacturing complexity is reduced, but mechanical protection and surface smoothness deteriorate
Solution Approach 1:
The patent makes the basecoat layer multi-functional by equipping it with both aesthetic functions (color, coverage) and protective functions (mechanical strength, surface smoothness). The basecoat contains reactive functional groups that enable it to form a crosslinked protective layer that can replace the traditional filler layer, providing mechanical protection and surface smoothness while eliminating one process step
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 approach results in multi-layer coatings with excellent stability against pinholes and high-quality visual and mechanical properties, comparable to standard processes, while eliminating the need for a separate curing step and enabling thicker basecoat layers without defects.
Implementation Method 1
an aqueous polyurethane-polyurea dispersion (PD) containing polyurethane-polyurea particles
Implementation Method 2
the basecoat layer and the clearcoat layer, which may also have been previously flashed off and/or partially dried, are then cured together (wet-on-wet process)
Data Source
Figure 1~3
AI summary
The invention relates to a method for producing a multi-layer lacquer finish on a metal substrate, wherein a base coat layer or a plurality of base coat layers directly following one another are produced directly on a metal substrate coated with a hardened electrophoretic dip coating, a clear lacquer layer is produced directly on one of or on the uppermost of the plurality of base coat layers, and then the one or the plurality of base coat layers and the clear lacquer layer are hardened together. The method is characterised in that at least one base coat used for producing the base coat layers comprises at least one aqueous polyurethane-polyurea dispersion (PD) containing polyurethane-polyurea particles, wherein the polyurethane-polyurea particles contained in the dispersion (PD) contain anionic groups and/or groups which can be converted into anionic groups and have a mean particle size of 40 to 2000 nm and a gel content of at least 50%.