Multilayer Coating Process Using Epoxy-Functional Silane Adhesion Promoter
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Solution Overview
Problem
Water-borne multilayer coatings in vehicle bodies face issues with unsatisfactory initial wet adhesion between layers and cohesion within the base coat or top coat layers, particularly under humidity strain, while maintaining other important coating properties like drying characteristics and optical properties.
Innovation Solution
A process involving a filler layer coated with an organic solvent-based composition containing a binder with active hydrogen, a polyisocyanate cross-linking agent, and an epoxy-functional silane, which improves adhesion and cohesion between layers and within the water-borne base coat or single-stage top coat layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If water-borne base coat and clear coat materials are used, then environmental friendliness is improved, but initial wet adhesion between layers deteriorates
Solution Approach 1:
An epoxy-functional silane adhesion promoter is introduced as an intermediary substance in the filler coating composition. This silane component acts as a chemical mediator that bridges the water-borne base coat layer and the clear coat layer, enabling effective adhesion between these layers while maintaining environmental friendliness through water-based formulations.
Solution Approach 2:
The invention changes the chemical composition parameters of the filler coating by incorporating specific epoxy-functional silane compounds with defined molecular structures (Formula I with specific R1, R2, R3 groups and n values). This parameter change in the chemical composition enables the filler layer to provide effective adhesion promotion for water-borne coatings.
2Object-affected harmful factors
If water-borne base coat materials are used, then environmental compliance is improved, but cohesion within the base coat layer deteriorates
Solution Approach 1:
The epoxy-functional silane in the filler coating composition serves as a mediator that enhances cohesion within the water-borne base coat layer by creating strong chemical bonds between the filler particles and the base coat resin, preventing cohesive failure while maintaining water-based formulation.
3Reliability
If humidity resistance is improved through adhesion promoters, then interlayer adhesion is improved, but drying characteristics deteriorate
Solution Approach 1:
The invention optimizes the concentration parameter of epoxy-functional silane to 0.5-7.0% by weight solids relative to total solids content. This precise parameter control ensures sufficient adhesion promotion without excessive viscosity increase or prolonged drying time, balancing adhesion improvement with acceptable drying characteristics.
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 process achieves excellent wet adhesion, high-pressure cleaning resistance, and improved cohesion within the water-borne layers without impairing other coating properties, such as drying characteristics and optical properties, even under severe conditions.
Implementation Method 1
a polyisocyanate cross-linking agent with free isocyanate groups
Implementation Method 2
at least one epoxy-functional silane of the general Formula (I)
Data Source
AI summary
The invention relates to a process for the multilayer coating of substrates, in particular vehicle bodies and vehicle body parts, comprising the steps: 1. applying a filler layer of a filler coating composition onto an optionally pre-coated substrate, 2. applying a base coat layer of a water-based base coat coating composition containing color-imparting and/or special effect-imparting pigments onto the filler layer, 3. applying a clear coat layer of a transparent clear coat coating composition onto the base coat layer and 4. curing the clear coat layer, optionally together with the filler layer and/or the base coat layer, wherein the filler coating composition being an organic solvent-based coating composition comprising: A) at least one binder with functional groups containing active hydrogen, B) at least one polyisocyanate cross-linking agent with free isocyanate groups and C) at least one epoxy-functional silane of the general Formula (I): X denoting the residues with m being 1-4, or epoxy cyclohexyl, R1, R2, R3 mutually independently meaning identical or different organic residues with 1 to 30 carbon atoms per molecule, providing that at least one of the residues is an alkoxy group with 1 to 4 carbon atoms and n is 2, 3 or 4.