Isocyanate-functional polyene clearcoat for waterborne basecoat adhesion
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Solution Overview
Problem
Multilayer coatings used in automotive refinish applications face challenges in achieving desired physical and chemical properties at ambient temperature, particularly with waterborne basecoats, which result in poor humidity resistance due to residual moisture affecting adhesion and performance.
Innovation Solution
A clear topcoat composition comprising an isocyanate-functional polyene and a polythiol, cured by radiation, is applied over a waterborne basecoat to enhance adhesion and performance by reacting with residual water, improving humidity resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If waterborne basecoat composition is used, then environmental compliance and ease of application are improved, but humidity resistance deteriorates due to residual moisture
Solution Approach 1:
The patent converts the harmful residual moisture in the waterborne basecoat into a beneficial element by using it as a reactant. The isocyanate-functional polyene in the clearcoat reacts with the residual water to form crosslinks, transforming the moisture that causes poor adhesion into a mechanism that enhances intercoat adhesion and humidity resistance.
Solution Approach 2:
The patent changes the chemical parameters of the clearcoat composition by incorporating isocyanate-functional polyene that can react with water. This parameter change enables the clearcoat to chemically interact with residual moisture, converting it from a detrimental factor into a crosslinking agent that improves coating performance and humidity resistance.
2Reliability
If heating is applied to achieve desired properties, then physical and chemical properties are improved, but energy consumption and process complexity increase
Solution Approach 1:
The patent replaces the thermal field (heating) with a chemical field mechanism. Instead of using heat to achieve crosslinking and desired coating properties, the system uses chemical reactions between isocyanate groups and water (moisture-curing) to achieve the same crosslinked network structure and coating performance at ambient temperature.
Solution Approach 2:
The patent utilizes a chemical phase transition from linear polymer chains to crosslinked network structure through the reaction between isocyanate-functional polyene and water. This chemical crosslinking process occurs at ambient temperature, eliminating the need for thermal processing while achieving the desired physical and chemical properties.
3Ease of operation
If conventional clearcoat is used over waterborne basecoat, then application simplicity is maintained, but intercoat adhesion deteriorates
Solution Approach 1:
The isocyanate-functional polyene acts as a chemical intermediary between the waterborne basecoat and the clearcoat system. It reacts with residual moisture at the basecoat interface to form crosslinks that anchor the clearcoat to the basecoat, thereby improving intercoat adhesion while maintaining the simplicity of the two-coat application process.
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 solution effectively addresses the issue of poor humidity resistance by ensuring better intercoat adhesion and performance properties, achieving improved results in multilayer coatings without the need for heating.
Implementation Method 1
the clear topcoat composition comprises: (a) an isocyanate functional polyene, and (b) a polythiol
Implementation Method 2
exposing the clear topcoat layer to radiation to cure the clear topcoat layer
Data Source
AI summary
A process for forming a color-clear multilayer coating on a substrate is disclosed. The clear basecoat is a waterborne coating and the clear topcoat is isocyanate containing and comprises a polyene and a polythiol. The isocyanate can be present as a separate component or can be an isocyanate-functional polyene.