Multi-Layer Coating Joint Curing Process
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Solution Overview
Problem
Current multi-layer coating processes in the automotive industry face challenges in achieving the required impact resistance and aesthetic properties, particularly when omitting the separate curing step of the coating agent applied directly to the electrocoating layer, leading to compromised mechanical resistance and stone chip resistance.
Innovation Solution
A method for producing multi-layer coatings on metallic substrates where a hardened electrophoretic paint layer is applied, followed by directly applying one or several aqueous basecoat layers and a clearcoat layer, with all layers being jointly cured, utilizing a specific linear hydroxy-functional reaction product containing compounds with two functional groups and an aliphatic or araliphatic hydrocarbon residue, eliminating the need for a separate curing step of the basecoat layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the separate curing step of the basecoat layer is omitted to simplify the manufacturing process, then productivity and ease of manufacture are improved, but the impact resistance and stone chip resistance of the coating deteriorate
Solution Approach 1:
The patent combines the curing of the basecoat layer with the curing of the clearcoat layer into a single joint curing step. This is achieved by applying the basecoat and clearcoat in sequence without intermediate drying, then curing both layers simultaneously in one oven cycle. The chemical composition of the basecoat (specifically using polymers with hydroxyl groups that react with isocyanate groups in the clearcoat) enables this merging while maintaining the mechanical properties of the cured coating system.
Solution Approach 2:
The basecoat layer is applied in a state that allows it to be cured in advance together with the clearcoat layer. The basecoat formulation (using specific polymers and crosslinking agents) enables it to remain stable during application and drying of the clearcoat, then cure simultaneously when the clearcoat is exposed to curing conditions. This preliminary preparation allows the simplified process while ensuring proper curing.
2Object-affected harmful factors
If aqueous coating agents are used to enhance ecological compatibility, then environmental performance is improved, but the adhesion and mechanical resistance may deteriorate
Solution Approach 1:
The patent uses specific polymer parameters in the aqueous basecoat formulation to ensure proper adhesion and mechanical resistance. The basecoat contains polymers with hydroxyl groups (such as polyurethanes, polyesters, or polyacrylates) with specific molecular weights and functional group densities. These parameter choices enable the aqueous coating to achieve strong adhesion to the electrocoated substrate and good mechanical properties after curing, despite using water as the carrier instead of organic solvents.
Solution Approach 2:
The basecoat is formulated as a composite system combining multiple polymer types (e.g., polyurethane-polyacrylate copolymers) with crosslinking agents (such as melamine resins or blocked polyisocyanates). This composite material approach allows the aqueous coating to achieve both ecological compatibility and reliable adhesion/mechanical resistance through the synergistic interaction of different polymer components and crosslinking mechanisms.
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 paint systems with excellent adhesion and impact resistance, meeting the stringent requirements of the automotive industry while using aqueous coating agents to enhance ecological compatibility.
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 applied electrophoretic paint is cured
Implementation Method 3
The base coat layer and the clear coat layer, which has also previously been flashed off and/or intermediately dried, are then hardened 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 layer or a plurality of directly consecutive base lacquer layers are produced directly on a metallic substrate coated with a hardened electrophoretic dip painting, a clear lacquer coat is produced directly on the one or the upper of the plurality of said base lacquer layers, and the one or the plurality of base lacquer coatings 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 coatings comprises at least one linear hydroxy-functional reaction product (R) having an acid number of less than 20 mg KOH/g, during the production of which at least one compound (v) is employed comprising two functional groups (v.1) and an aliphatic or araliphatic hydrocarbon group (v.2) having 12 to 70 hydrocarbon atoms arranged between the functional groups.