Self-Crosslinking Polyurethane Dispersion for Solvent Resistance
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Solution Overview
Problem
One-pack waterborne polyurethane coatings lack the solvent resistance and chemical resistance required for many applications, and existing blocked polyisocyanate crosslinkers face issues with compatibility and storage stability due to the lack of active groups for high-density cross-linking.
Innovation Solution
A high-temperature self-crosslinking aqueous polyurethane dispersion containing both blocked NCO groups and hydroxyl groups on the macromolecular structure, which can form a high-density cross-linked structure upon heating without the need for additional waterborne resins or crosslinkers, prepared using specific reactants and a multi-step reaction process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If one-pack waterborne polyurethane is used for convenient application, then ease of operation is improved, but solvent resistance and chemical resistance deteriorate
Solution Approach 1:
The patent applies preliminary action by pre-introducing hydroxyl groups into the polyurethane dispersion during synthesis, so that when the blocked NCO groups are deblocked by heating, the crosslinking reaction can immediately occur without requiring separate addition of crosslinkers or other waterborne resins. This preliminary preparation enables the one-pack system to achieve high-density crosslinking and excellent solvent/chemical resistance while maintaining application convenience.
2Reliability
If blocked polyisocyanate crosslinker is used to improve crosslinking performance, then solvent resistance and chemical resistance are improved, but compatibility and storage stability deteriorate due to lack of active groups
Solution Approach 1:
The patent merges the functions of the polyurethane dispersion and crosslinker into a single self-crosslinking polyurethane dispersion. The hydroxyl groups and blocked NCO groups are incorporated into the same macromolecular structure, eliminating the need for separate crosslinker components. This integration resolves compatibility issues and storage stability problems associated with mixing different waterborne resins and crosslinkers, while still achieving high-density crosslinking for excellent solvent and chemical resistance.
3Reliability
If additional waterborne resins and crosslinkers are added to achieve high-density cross-linking, then solvent resistance and chemical resistance are improved, but device complexity and formulation complexity increase
Solution Approach 1:
The patent creates a universal self-crosslinking polyurethane dispersion that performs multiple functions: it provides the base polymer matrix, contains blocked NCO groups for crosslinking, and includes hydroxyl groups for high-density crosslinking. This multi-functional material eliminates the need for separate crosslinkers and additional waterborne resins, simplifying the formulation to a true one-pack system while achieving excellent solvent and chemical resistance through high-density crosslinking.
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 method enables the production of a one-pack waterborne coating with excellent physical and chemical properties, achieving high-density cross-linking and improved performance without additional crosslinkers or resins, demonstrating enhanced solvent resistance, water resistance, and stability.
Implementation Method 1
the blocked isocyanate (NCO) is deblocked by heating. After that the deblocked NCO is cross-linked with the active groups on the other waterborne resins
Implementation Method 2
the deblocked NCO is cross-linked with the active groups on the other waterborne resins to obtain a high-performance one-pack waterborne coating
Data Source
AI summary
A method for preparing a high-temperature self-crosslinking aqueous polyurethane dispersion. By using isocyanate (NCO) blocking agent to block part of the NCO, and using the hydroxyalkyl ethylenediamine chain extender in the post-chain extension stage to introduce hydroxyl groups, the polymer macromolecular structure containing both blocked NCO groups and hydroxyl groups can be prepared. The aqueous polyurethane dispersion does not need to mix with other waterborne resins and crosslinkers when applied. A sufficient cross-linking reaction is performed between the NCO released and hydroxyl groups on the polymer macromolecular chain to form a high-density cross-linked structure when curing at 100-150° C. for 20-30 min, thus obtaining a high-performance waterborne coating that can be used in the form of one-pack.