Polyisocyanate Curing Agent for Blister-Free Coatings
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Solution Overview
Problem
Aqueous two-pack urethane coating compositions face challenges with polyisocyanate curing agents in terms of extensibility at low temperatures and blister formation in thick films, particularly in industrial and automotive paints, where existing solutions either lack environmental sustainability or insufficiently address film durability.
Innovation Solution
A polyisocyanate curing agent is developed by reacting a specific range of isocyanate groups with a polyalkylene glycol alkyl ether and a polyester polyol, optimizing the urethane group ratio to enhance water dispersibility, reduce blister occurrence, and improve film elongation and hardness at low temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If polyisocyanate curing agent is used in aqueous coating composition, then water dispersibility is improved, but reaction with water generates carbon dioxide causing blisters
Solution Approach 1:
The patent modifies the polyisocyanate curing agent by controlling the average number of isocyanate functional groups (1.8-4.0) and reacting with specific polyols to reduce reactivity with water while maintaining water dispersibility through emulsification
Solution Approach 2:
The patent uses polyalkylene glycol alkyl ethers and polyester polyols as intermediaries to modify the polyisocyanate, creating a structure that disperses in water without directly exposing isocyanate groups to water, thereby preventing CO2 generation and blister formation
2Temperature
If coating film is formed at low temperature, then environmental protection is improved, but extensibility becomes insufficient causing peeling
Solution Approach 1:
The patent creates a composite curing agent system combining modified polyisocyanate with specific polyols that maintain flexibility and extensibility at low temperatures, preventing film peeling while enabling environmentally friendly low-temperature curing
Solution Approach 2:
The patent adjusts the molecular structure parameters of the curing agent by controlling the polyol type and isocyanate functional group count, creating a formulation that remains flexible and extensible at low curing temperatures
3Length of stationary object
If film thickness is increased, then coating protection is improved, but blisters generate deteriorating appearance
Solution Approach 1:
The patent modifies the chemical parameters of the curing agent to reduce water reactivity and CO2 generation, enabling thick film formation without blister formation that would compromise appearance
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 polyisocyanate curing agent with improved water dispersibility, reduced blister formation, and enhanced film extensibility and hardness, even at low temperatures, while being environmentally friendly by minimizing solvent use and improving coating film properties.
Implementation Method 1
the polyisocyanate curing agent is not easily dispersed in water, but easily reacts with water to generate carbon dioxide
Data Source
AI summary
The present invention provides a polyisocyanate curing agent including a structural unit derived from a diisocyanate, a structural unit derived from a polyester polyol, and a structural unit derived from the following general formula (1), wherein a content of the isocyanate group is 5.0 to 20.0% by mass and a molar ratio between a urethane group derived from a polyalkylene glycol alkyl ether and a urethane group derived from the polyester polyol is 0.03 to 2.5, (in formula (1), R1 is an alkylene group having 1 to 4 carbon atoms, R2 is an alkyl group having 1 to 4 carbon atoms, and an average number of n is 4.0 to 20.0).