Coating Composition Using Mercapto Carboxylic Acid to Control Pinholes
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Solution Overview
Problem
Existing coating compositions face challenges in achieving a balance of high curing rate, long pot life, low VOC content, and good appearance and hardness, particularly in motor vehicle exterior finishes, while also providing flexibility, scratch resistance, gloss, durability, and resistance to chemicals and UV radiation.
Innovation Solution
A coating composition comprising a polyisocyanate, a polyol with an average functionality of more than 3 hydroxyl groups, a metal-based curing catalyst, and a mercapto carboxylic acid, which excludes carboxylic acids with a carbonyl group in conjugation with a π-electron system, to optimize curing speed, pot life, and appearance properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a high curing catalyst load is used to obtain a short drying time, then the curing rate is improved, but foam stabilization occurs leading to pinholes in the dried coating layer
Solution Approach 1:
The patent uses a specific mercapto carboxylic acid with particular molecular structure parameters (non-conjugated carbonyl group) to modify the catalyst system's behavior, achieving optimal curing rate while preventing pinhole formation through controlled foam stabilization
2Object-affected harmful factors
If a lower amount of curing catalyst is used, then the risk of coating defects is decreased, but the drying time increases and hardness decreases
Solution Approach 1:
The patent optimizes the catalyst system by selecting specific mercapto carboxylic acids with defined molecular parameters, enabling effective curing at lower catalyst loads while maintaining acceptable drying times and coating hardness through enhanced catalyst efficiency
3Loss of substance
If a high non-volatile content is used to reduce VOC, then the coating viscosity increases, but the balance of pot life, appearance properties, and curing rate becomes difficult to achieve
Solution Approach 1:
The patent addresses the high viscosity challenge by selecting mercapto carboxylic acids with specific molecular weight and structural parameters that maintain adequate pot life and processability even at high solid contents, while achieving the desired balance of curing rate and appearance properties
Solution Approach 2:
The patent creates a composite catalyst system combining metal-based catalysts with specific mercapto carboxylic acids, where the synergistic interaction between components enables effective curing at high solid contents while maintaining favorable processing 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 composition achieves a favorable balance of properties, including low VOC content, high cure speed, and long pot life, resulting in coatings with improved appearance, hardness, flexibility, and resistance to chemicals and UV radiation, suitable for motor vehicle exterior finishes.
Implementation Method 1
a metal based catalyst for the addition reaction of isocyanate groups and hydroxyl groups
Implementation Method 2
coating composition comprising a polyisocyanate, a polyol having an average functionality of more than 3 hydroxyl groups per molecule
Data Source
AI summary
The invention relates to a non-aqueous coating composition comprisinga. a polyisocyanate,b. a polyol having an average functionality of more than 3 hydroxyl groups per molecule,c. a metal based curing catalyst for the addition reaction of isocyanate groups and hydroxyl groups, andd. a mercapto carboxylic acid,wherein the coating composition does not contain a carboxylic acid wherein the carbonyl group of the carboxylic acid is in conjugation with a π-electron system.