Aqueous Polyurethane Dispersion Particle Size Control
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Solution Overview
Problem
Existing processes for preparing aqueous polyurethane dispersions struggle to achieve a balance between small average particle size and high density of COOH and salt groups, which is crucial for effective coating applications.
Innovation Solution
A process involving the reaction of at least one first polyisocyanate with a polyol carrying COOH groups, followed by treatment with another polyol and optionally additional polyisocyanates, to control the reaction index and achieve a composition with a high density of COOH and salt groups, resulting in a polyurethane/poly(meth)acrylate hybrid polymer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional processes are used to prepare aqueous polyurethane dispersions, then the production is relatively simple, but the particle size is large and the density of COOH and salt groups is low
Solution Approach 1:
The patent divides the polyurethane synthesis into multiple sequential stages: Stage 1 forms a prepolymer with controlled NCO content, Stage 2 adds polyol to control molecular weight and particle formation, and Stage 3 optionally adds more polyisocyanate to adjust COOH group density. This staged approach allows precise control of particle size and functional group distribution that cannot be achieved in conventional single-step processes.
Solution Approach 2:
The patent performs preliminary formation of NCO-functional prepolymer in Stage 1 before adding polyol in Stage 2. This preliminary action establishes the core structure and functional group distribution early in the process, enabling better control over final particle characteristics and COOH group density.
2Quantity of substance
If the reaction is allowed to proceed to high conversion, then the COOH group density increases, but the particle size also increases
Solution Approach 1:
The patent uses periodic addition of reagents across three stages: Stage 1 forms prepolymer, Stage 2 adds polyol to control particle growth, and Stage 3 optionally adds more polyisocyanate. This periodic action allows the system to achieve high COOH group density through controlled, incremental reactions rather than continuous high-conversion processing, thereby limiting particle size increase.
Solution Approach 2:
The patent changes key reaction parameters at each stage: Stage 1 uses specific NCO:OH ratios to form prepolymer, Stage 2 adjusts polyol addition rate and NCO content to control particle growth, and Stage 3 modifies polyisocyanate addition to tune COOH density. These parameter changes enable decoupling of COOH group density from particle size, achieving high density with small particles.
3Volume of moving object
If polyol is added to terminate the reaction early, then particle size is reduced, but the density of COOH and salt groups decreases
Solution Approach 1:
The patent maintains continuous useful action by adding polyisocyanate in Stage 3 after polyol termination in Stage 2. This additional stage continues the build-up of COOH groups without significant particle growth, as the system is already terminated. This ensures high COOH group density is achieved while maintaining small particle size from the earlier termination.
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 process yields aqueous compositions with small average particle sizes and high COOH and salt group densities, enhancing coating performance and stability, including storage stability and resistance to electrolytes.
Implementation Method 1
reacting at least one first polyisocyanate (A1) with at least one polyol carrying at least one COOH group (BX)
Data Source
AI summary
The present invention relates a process of the present invention for the preparation of an aqueous composition comprising a polyurethane carrying COOH groups and/or salt groups thereof, comprises the steps of (i) reacting at least one first polyisocyanate (A1) with at least one polyol carrying at least one COOH group (BX) and optionally at least one first polyol carrying no COOH group (B1) to form a first composition (C1), (ii) treating the first composition (C1) obtained in step (i) with at least one second polyol carrying no COOH group (B2), and optionally with at least one second polyisocyanate (A2), to form a second composition (C2), and (iii) optionally treating the second composition (C2) obtained in step (ii) with at least one third-polyisocyanate (A3), to form a third composition (C3), wherein step (i) is stopped at a reaction index in the range of 0.05 to 0.94, wherein reaction index=reaction rate×[mol initial NCO groups of all A1/(mol initial OH groups of all BX and, if present, mol initial OH groups of all B1)] (formula 1) wherein reaction rate=1 minus (mol NCO groups of C1/mol initial NCO groups of all A1), and to an aqueous composition comprising a polyurethane carrying COOH groups and/or salt groups thereof obtainableby this process, to a process for the preparation of an aqueous composition comprising a polyurethane/poly(meth)acrylate hybrid polymer using the aqueous composition comprising a polyurethane carrying COOH groups and/or salt groups thereof of the present invention, to aqueous compositions comprising a polyurethane/poly(meth)acrylate hybrid polymer obtainable by the this process, to coating compositions comprising the aqueous composition comprising a polyurethane carrying COOH groups and/or salt groups thereof or the aqueous compositions comprising a polyurethane/poly(meth)acrylate hybrid polymer, and to substrates coated with these coating compositions.