Self-Emulsifying Blocked Polyisocyanate for Low-Temperature Curing
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Solution Overview
Problem
Current low-temperature curable cathodic electrodeposition coating materials face challenges with reduced stability and performance issues, such as long-term storage and working stability, leading to poor appearance and properties of the coating films, despite improved reactivity.
Innovation Solution
The use of a self-emulsifying blocked polyisocyanate with neutralized amine in cathodic electrodeposition coating materials, which is prepared by reacting a polyurethane prepolymer with a blocking agent and an amine compound, and then neutralizing the resulting amine-containing blocked polyisocyanate, allows for stable dispersion without added surfactants, enhancing stability and application performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If conventional blocked polyisocyanates are used to achieve low-temperature curing, then curing temperature is reduced, but storage stability and working stability deteriorate
Solution Approach 1:
The patent introduces a self-emulsifying blocked polyisocyanate as an intermediary substance that enables low-temperature curing while maintaining stability. This compound acts as a mediator between the conflicting requirements of low curing temperature and high storage/working stability, resolving the technical contradiction through its unique molecular structure that combines blocked isocyanate functionality with self-emulsifying properties
Solution Approach 2:
The invention changes the chemical parameters of the polyisocyanate compound by introducing a self-emulsifying blocked structure. This parameter change allows the curing agent to function at lower temperatures while maintaining colloidal stability in aqueous medium, thereby achieving both low curing temperature and high stability simultaneously
2Temperature
If conventional blocked polyisocyanates are used to achieve low-temperature curing, then curing temperature is reduced, but coating film appearance and properties deteriorate
Solution Approach 1:
The self-emulsifying blocked polyisocyanate serves as an intermediary that ensures proper dispersion and reactivity, leading to high-quality coating films. Its unique structure mediates between the low curing temperature requirement and the need for excellent coating film appearance and properties
Solution Approach 2:
The self-emulsifying property allows the blocked polyisocyanate to automatically form stable dispersions without external surfactants, ensuring uniform distribution and consistent coating quality. This self-service capability maintains coating film appearance and properties while enabling low-temperature curing
3Stability of the object's composition
If emulsifiers are added to disperse blocked polyisocyanate, then dispersion is achieved, but system complexity and potential instability increase
Solution Approach 1:
The blocked polyisocyanate compound possesses self-emulsifying capability, allowing it to automatically form stable dispersions in aqueous medium without requiring external emulsifiers. This self-service property simplifies the system by eliminating additional components while maintaining dispersion stability
Solution Approach 2:
The invention extracts the emulsifying function from separate additives and integrates it directly into the blocked polyisocyanate molecule itself. This consolidation removes the need for additional emulsifier components, reducing system complexity while achieving stable dispersion
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
This approach enables cathodic electrodeposition coating materials to be cured at lower temperatures with improved stability, corrosion resistance, and enhanced application performance, including reduced VOC and increased throw power, while maintaining film quality.
Implementation Method 1
a blocked polyisocyanate having neutralized amine, which is obtainable or obtained by a process comprising steps of (i) reacting a polyurethane prepolymer containing isocyanate groups as polyisocyanate with a blocking agent selected from oximes, pyrazoles and active methylene compounds, to provide a partially blocked polyisocyanate, (ii) reacting remaining isocyanate groups in the partially blocked polyisocyanate with an amine compound having active hydrogen, to provide an amine-containing blocked polyisocyanates, and (iii) neutralizing the amine-containing blocked polyisocyanates with an acid
Implementation Method 2
During electrodeposition coating, the substrate to be coated is used as the cathode. A current is applied between the cathode and an anode as counter electrode such that the micelles containing the neutralized resin component and the curing component in the coating bath are deposited on the metal substrate to form a coating film
Data Source
AI summary
Disclosed herein is a cathodic electrodeposition coating composition, which includes (A) a cationic amino-containing epoxy resin, (B) a blocked polyisocyanate having neutralized amine, which is obtained by a process including steps of (i) reacting a polyurethane prepolymer containing isocyanate groups with at least one blocking agent selected from the group consisting of oximes, pyrazoles and active methylene compounds, to provide a partially blocked polyisocyanate, (ii) reacting remaining isocyanate groups in the partially blocked polyisocyanate with an amine compound having active hydrogen, to provide an amine-containing blocked polyisocyanates, and (iii) neutralizing the amine-containing blocked polyisocyanates with an acid, and (C) a curing catalyst. Further disclosed herein are a process for preparing the cathodic electrodeposition coating composition, and a coating bath for the cathodic electrodeposition including the cathodic electrodeposition coating composition.