Polycarbonate Coated Article Adhesion via Hydroxyl Content
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Solution Overview
Problem
Existing coated articles made from polycarbonate materials in automotive applications, particularly front panels of electric vehicles, face challenges in achieving sufficient coating adhesion and minimizing negative impacts on mechanical properties, such as brittle impact failure.
Innovation Solution
A coated article comprising a thermoplastic composition with at least 50 wt.% of a first polycarbonate having a terminal hydroxyl content of at least 500 ppm, coated with a two-component polyurethane layer obtained by reacting di- or tri-isocyanate and polyol, where part of the isocyanate groups react with phenolic OH groups on the polycarbonate chains, forming a chemically bonded, at least partially cross-linked coating layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a protective coating is applied to polycarbonate carrier, then protection from scratching and weathering is improved, but coating adhesion is insufficient and delamination occurs
Solution Approach 1:
The invention changes the chemical parameter of the polycarbonate by ensuring it has a terminal hydroxyl content of at least 500 ppm. This parameter change enables chemical bonding between the polycarbonate carrier and the polyurethane coating through reaction between the hydroxyl groups and isocyanate groups, thereby improving coating adhesion and preventing delamination.
Solution Approach 2:
The terminal hydroxyl groups on the polycarbonate chains act as an intermediary that facilitates chemical bonding between the carrier and the coating. These hydroxyl groups react with the isocyanate groups in the polyurethane coating, creating a chemical bridge that ensures strong adhesion and prevents delamination over time.
2Strength
If conventional polycarbonate composition is used, then manufacturing is simple, but impact properties show brittle failure
Solution Approach 1:
The invention specifies a terminal hydroxyl content of at least 500 ppm as a critical parameter change in the polycarbonate composition. This parameter change improves impact resistance by enabling ductile impact failure rather than brittle failure, while maintaining compatibility with conventional manufacturing processes like injection molding.
3Reliability
If polyurethane coating is applied directly on polycarbonate, then coating adhesion is improved through chemical bonding, but terminal hydroxyl content must be controlled
Solution Approach 1:
The invention establishes a minimum threshold of 500 ppm for terminal hydroxyl content in the polycarbonate carrier. This parameter specification ensures sufficient chemical bonding capability with the polyurethane coating while providing a clear manufacturing target that balances adhesion requirements with production feasibility.
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 achieves improved coating adhesion and reduced negative effects on mechanical properties, leading to enhanced ductile impact failure resistance and aesthetic durability, particularly suitable for automotive front panels.
Implementation Method 1
part of the isocyanate groups react with phenolic OH groups on the polycarbonate chains, forming a chemically bonded, at least partially cross-linked coating layer
Implementation Method 2
obtained by reacting at least one di- or tri-isocyanate and at least one polyol, where part of the isocyanate groups react with phenolic OH groups on the polycarbonate chains, forming a chemically bonded, at least partially cross-linked coating layer
Data Source
AI summary
The present invention relates to an article comprising a carrier provided at least in part with a coating layer, wherein i) said carrier comprises or consists of a thermoplastic composition, said thermoplastic composition comprising polycarbonate, ii) said coating layer is applied directly on said carrier and comprises or consists of polyurethane obtained by reacting at least one di-or-tri-isocyanate and at least one polyol, iii) said polycarbonate comprises, based on the weight of the polycarbonate, at least 50 wt.% of a first polycarbonate having a terminal hydroxyl content of at least 500 ppm.