Polyurea Sag Control in Carbonyl-Hydrazide Coatings
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Solution Overview
Problem
Aqueous coating compositions with carbonyl-hydrazide crosslinking systems face challenges in achieving desired thixotropy using conventional sag control agents, which often adversely affect gloss and film clarity, and lack effective sag control agents suitable for these systems.
Innovation Solution
The use of polyurea adducts formed in situ from tris(isocyanate) isocyanurates and ether amines as sag control agents within the carbonyl-hydrazide crosslinking systems, which react to create a polyurea adduct that enhances thixotropy and improves film appearance by eliminating gel particles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If conventional sag control agents are used in aqueous coating compositions with carbonyl-hydrazide crosslinking systems, then sagging is controlled, but gloss and film clarity are adversely affected
Solution Approach 1:
The invention changes the chemical parameters by using polyurea adducts with specific molecular structures and compositions (formed from isocyanates and amines) instead of conventional sag control agents. This parameter change allows achieving sag control while maintaining film clarity and gloss, as the polyurea adducts provide thixotropic behavior without the adverse effects of traditional agents on film appearance
Solution Approach 2:
The invention employs composite materials by combining polyurea adducts (formed from isocyanate and amine components) within the aqueous coating composition containing carbonyl-hydrazide crosslinking systems. This composite approach creates a synergistic effect where the polyurea adduct provides sag control functionality while the carbonyl-hydrazide system maintains crosslinking and film formation, resulting in both good sag resistance and film appearance
2Object-generated harmful factors
If waterborne thermoplastic vinyl polymer dispersions or thermoplastic waterborne polyurethane dispersions are used, then VOC emissions are reduced, but chemical resistance, water resistance, blocking resistance and low temperature flexibility are insufficient
Solution Approach 1:
The invention changes the chemical composition parameters by introducing carbonyl-hydrazide crosslinking systems into waterborne polymer dispersions. This transformation converts thermoplastic waterborne polymers into thermosetting crosslinked networks, fundamentally changing the performance characteristics to achieve chemical resistance, water resistance, blocking resistance and low temperature flexibility while maintaining low VOC emissions
Solution Approach 2:
The carbonyl-hydrazide crosslinking reaction involves oxidation processes where carbonyl groups react with hydrazide groups to form crosslinked structures. This chemical transformation accelerates the development of performance properties by creating a three-dimensional network structure that provides enhanced chemical resistance, water resistance, blocking resistance and low temperature flexibility compared to simple thermoplastic dispersions
3Ease of operation
If thixotropic behavior is achieved through conventional means in aqueous coating compositions, then sagging is reduced, but the coating compositions lack effective sag control agents suitable for carbonyl-hydrazide crosslinking systems
Solution Approach 1:
The polyurea adducts serve as intermediary substances that bridge the gap between sag control functionality and carbonyl-hydrazide crosslinking system compatibility. These adducts, formed from isocyanates and amines, act as mediators that provide thixotropic behavior without interfering with the carbonyl-hydrazide crosslinking mechanism, thus enabling effective sag control in this specific system
Solution Approach 2:
The polyurea adducts are formed in situ within the coating composition through the reaction of isocyanates and amines, allowing the system to self-generate the sag control functionality. This self-service approach eliminates the need for external sag control agents that may not be compatible with carbonyl-hydrazide systems, as the system creates its own thixotropic modifiers through internal chemical reactions
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 polyurea adducts effectively control sagging and improve the appearance of films by providing enhanced thixotropy and maintaining film clarity, addressing the limitations of conventional sag control agents in aqueous coating compositions.
Implementation Method 1
crosslinking of the polymers takes place on drying through formation of a Schiff's base
Implementation Method 2
Removal of water from the system, such as by evaporation during air drying, drives the reaction to the crosslinked product
Implementation Method 3
these coating compositions have a consistency that is gel-like at rest, but fluid when agitated. This rheological behavior is referred to as thixotropy
Data Source
AI summary
A process for the preparation of a thixotropic aqueous coating composition comprising the steps of: i) providing an aqueous dispersion of a binder system comprising carbonyl and hydrazide functional groups for crosslinking; and ii) reacting in the aqueous dispersion, an ether amine with a tris(isocyanate) isocyanurate to form a polyurea sag control agent.