Multilayer Vehicle Coating Adhesion via Epoxy Silane
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Solution Overview
Problem
Water-borne multilayer coatings for vehicle bodies and parts face challenges with unsatisfactory initial wet adhesion between layers, particularly between the filler and base coat, and between the base coat and clear coat, as well as within the base coat layer itself, while maintaining other important coating properties like drying characteristics and optical properties.
Innovation Solution
A process involving a filler layer, a water-based base coat layer, and a clear coat layer, where the filler and clear coat compositions include epoxy-functional silane compounds, ensuring excellent adhesion and cohesion without compromising drying characteristics, stability, or optical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If water-borne base coat materials are used to achieve environmentally friendly coating, then environmental compatibility is improved, but initial wet adhesion between layers deteriorates
Solution Approach 1:
The patent introduces an intermediary layer (silane-modified polymer or zinc phosphate conversion layer) between the water-borne base coat and the clear coat. This intermediary layer acts as a bridge that provides both adhesion to the water-borne base coat and bonding to the clear coat, resolving the adhesion problem while maintaining the environmental benefits of water-borne materials.
Solution Approach 2:
The patent modifies the chemical parameters of the coating system by introducing silane-modified polymers and zinc phosphate conversion layers. These parameter changes enable the water-borne base coat to achieve proper adhesion to the clear coat by altering the surface chemistry and creating reactive groups that form strong bonds.
2Loss of substance
If water-borne base coat materials are used to reduce solvent content, then VOC emission is reduced, but cohesion within the base coat layer deteriorates
Solution Approach 1:
The patent creates a composite coating system combining water-borne base coat with silane-modified polymer intermediaries and zinc phosphate conversion layers. This composite structure provides both the environmental benefits of low solvent content and the mechanical strength of cross-linked networks through silane-zinc phosphate reactions.
Solution Approach 2:
The patent replaces the mechanical cohesion provided by solvent-based systems with chemical bonding through silane-zinc phosphate cross-linking. This substitution allows the coating to achieve cohesion through chemical reactions rather than physical solvent binding, enabling low solvent content while maintaining structural integrity.
3Reliability
If epoxy-functional silane compounds are added to filler and clear coat compositions to improve adhesion, then wet adhesion is improved, but formulation complexity increases
Solution Approach 1:
The patent makes the epoxy-functional silane compound serve multiple functions: it acts as an adhesion promoter between layers, provides cross-linking in the clear coat, and enables reaction with zinc phosphate to form strong bonds. This multi-functionality reduces the need for multiple separate additives, thereby limiting the increase in formulation complexity.
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 and dry adhesion, high-pressure cleaning resistance, and improved cohesion within the base coat layer, even under severe conditions, while maintaining the integrity of other coating properties.
Implementation Method 1
the filler and clear coat coating compositions each comprise: 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
Implementation Method 2
at least one polyisocyanate cross-linking agent with free isocyanate groups
Implementation Method 3
at least one epoxy-functional silane of the general Formula (I): X denoting the residues with m being 1-4, or 3,4 - epoxycyclohexyl
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 and the transparent clear coat coating composition being organic solvent-based coating compositions 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): (I) denoting the residues (II) with m being 1 4, or 3,4 - epoxycyclohexyl, 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.