Blocked Polyisocyanate Crosslinking Agent for Low VOC Coatings
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Solution Overview
Problem
Existing automotive coating compositions using blocked polyisocyanates face challenges with high solvent content, leading to VOC issues and inadequate reactivity between isocyanates and polyacrylate/polyols, resulting in poor flowability and storage stability.
Innovation Solution
A blocked polyisocyanate crosslinking agent is developed through reactions involving aliphatic or cycloaliphatic polyisocyanates and beta-diketones, combined with (meth)acrylates, which enables dual curing via radical polymerization and reaction with polyacrylate/polyols, improving flowability and storage stability while reducing VOCs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If traditional blocked polyisocyanates are used as curing agents, then the coating can be baked, but the solvent content remains high leading to VOC problems
Solution Approach 1:
The patent changes the chemical parameters of the polyisocyanate by introducing a blocked structure with specific NCO groups that have reduced volatility. The blocking agent modifies the physical and chemical properties of the isocyanate, allowing it to remain reactive while reducing solvent content and VOC emissions during the curing process
Solution Approach 2:
The invention creates a composite curing system by combining blocked polyisocyanate with polyacrylate and/or polyol components. This composite approach enables dual curing mechanisms (isocyanate-polyol reaction and radical polymerization) that allow for reduced solvent content while maintaining effective crosslinking and coating performance
2Object-affected harmful factors
If solvent content is reduced, then VOC emissions decrease, but the reaction between isocyanates and polyacrylate/polyols becomes inadequate
Solution Approach 1:
The blocked polyisocyanate structure changes the reactivity parameters of the NCO groups, enabling them to remain sufficiently reactive at lower solvent concentrations. The blocking and deblocking mechanism ensures that the isocyanate groups become active at the appropriate stage, maintaining reaction completeness even with reduced solvent content
Solution Approach 2:
The composite curing system combines multiple reaction pathways (isocyanate-polyol urethane formation and acrylate radical polymerization) that can proceed effectively at lower solvent levels. This multi-mechanism approach ensures reliable and complete curing reactions without requiring high solvent content
3Ease of operation
If the coating composition uses conventional curing agents, then it can be applied, but the flowability and storage stability are poor
Solution Approach 1:
The blocked polyisocyanate structure modifies the viscosity and reactivity parameters of the curing agent, improving flowability during application. The blocking agent prevents premature reaction while maintaining appropriate rheological properties, and the controlled deblocking during curing ensures stable crosslinking without compromising storage stability
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 provides a coating composition with excellent flowability, storage stability, and dual-curing capabilities, resulting in a tack-free, high-performance coating layer with enhanced hardness, solvent resistance, elasticity, and adhesion properties.
Implementation Method 1
dual curing via radical polymerization and reaction with polyacrylate/polyols
Implementation Method 2
reaction of isocyanates and polyacrylate/polyols
Data Source
AI summary
Described herein is a blocked polyisocyanate crosslinking agent obtained from reactions of components including a). at least one polyisocyanate selected from the group consisting of aliphatic polyisocyanate, cycloaliphatic polyisocyanate and polyisocyanate-functional polymer and b). at least one beta-diketone. Also described herein is a method of preparing a blocked polyisocyanate crosslinking agent as well as coating compositions including the blocked polyisocyanate crosslinking agent.