Aqueous Polyurethane Dispersion Stability via Monofunctional Chain Extension
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Solution Overview
Problem
Existing aqueous polyurethane dispersions face challenges with storage stability, chemical resistance, and water resistance, particularly when produced without N-methylpyrrolidone (NMP) and hydrazine, which are teratogenic and carcinogenic, respectively, and result in inadequate hardness and yellowing resistance in coatings.
Innovation Solution
The development of aqueous polyurethane dispersions using monofunctional components such as monoalcohols and monoamines with specific molecular weights, combined with polyisocyanates and polyols, to achieve a hard segment content of 58-80% and improved storage stability without NMP and hydrazine, utilizing a process that includes prepolymerization and chain extension followed by solvent removal by distillation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If NMP is used as a solvent in polyurethane production, then viscosity reduction and dissolution of dimethylolpropionic acid are improved, but teratogenicity and environmental harm increase
Solution Approach 1:
The patent removes NMP from the polyurethane production system and replaces it with a water-based dispersion process using monofunctional components. This extraction of the harmful solvent eliminates teratogenicity while maintaining manufacturing ease through alternative hydrophilization methods that do not require NMP for dissolution or viscosity control.
Solution Approach 2:
The patent changes the chemical parameters of the production system by using monofunctional components with specific molecular weights (monoalcohols Mn 32-145 g/mol and monoamines Mn <147 g/mol) instead of NMP. This parameter change achieves the desired polyurethane properties through different chemical mechanisms, eliminating the need for the harmful solvent while maintaining ease of manufacture.
2Reliability
If hydrazine is used for chain extension to improve yellowing resistance, then yellowing resistance is improved, but carcinogenicity increases
Solution Approach 1:
The patent extracts hydrazine from the chain extension process and replaces it with monofunctional components (monoalcohols and monoamines). This removal eliminates carcinogenicity while maintaining yellowing resistance through the specific chemical structure and properties of the alternative components that do not promote yellowing.
Solution Approach 2:
The patent uses readily available monofunctional components with low molecular weights that can be easily incorporated into the polyurethane system. These components serve the dual purpose of chain extension and providing yellowing resistance without the long-term stability and storage issues associated with hydrazine, while being safer and more environmentally friendly.
3Object-affected harmful factors
If polyurethane dispersions are produced without NMP and hydrazine, then safety and environmental compatibility are improved, but storage stability and chemical resistance deteriorate
Solution Approach 1:
The patent optimizes the molecular weight parameters of the monofunctional components used (monoalcohols Mn 32-145 g/mol and monoamines Mn <147 g/mol) to achieve the desired balance between safety and performance. These specific parameter ranges ensure adequate storage stability and chemical resistance while maintaining the safety benefits of being free from NMP and hydrazine.
Solution Approach 2:
The patent creates a composite polyurethane system using combinations of monofunctional components, polyisocyanates, and polyols to achieve the desired property profile. This composite approach allows the dispersion to gain storage stability and chemical resistance from the synergistic interactions between components while remaining free from harmful substances.
4Strength
If hard segment content is increased to improve hardness, then coating hardness is improved, but storage stability deteriorates
Solution Approach 1:
The patent carefully controls the molecular weight parameters of the monofunctional components and the hard segment content (58-80% by weight) to achieve an optimal balance. By using monofunctional components with specific low molecular weights, the patent enables high hard segment content to be achieved while maintaining storage stability, as the small molecular weight components provide adequate flexibility and prevent excessive brittleness.
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 resulting polyurethane dispersions exhibit improved storage stability for at least 6 weeks at 40°C, enhanced chemical and water resistance, and hardness exceeding 90 seconds, while being free from NMP and hydrazine, making them suitable for various coating applications.
Implementation Method 1
The invention relates to aqueous polyurethane dispersions with a high proportion of hard segments... produced by reacting the components a), b), c) and d)
Implementation Method 2
whereby the process comprises the following steps: I.1) first, in a first step, an NCO prepolymer solution in a concentration of 66 to 98% of a solvent with a boiling point below 100 °C at normal pressure by reacting the components
Data Source
AI summary
A hydrazine-free aqueous polyurethane dispersion comprises (a) polyisocyanate(s), (b) polyol(s) having average molar weights (M n) of 500-6000 g/mol; (c) polyol(s) having M n of 62-500 g/mol; (d) compound(s) containing an ionic group or a group capable of forming an ionic group; (e) polyamine(s) having M n below 500 g/mol; (f) optionally monoalcohol(s) having M n of 32-145 g/mol; and (g) optionally monoamine(s) having M n of less than 147 g/mol. At least one of (f) and (g) is used. The fraction of (f) and/or (g) is >=0.4-1.26 wt.%; and the fraction of (c) is greater than 5.5-22 wt.%. An independent claim is included for a process of preparing the hydrazine-free aqueous polyurethane dispersion, comprising preparing isocyanate (NCO) prepolymer solution in a concentration of 66-98% in a solvent having a boiling point below 100[deg]C, under atmospheric pressure by reacting components (a), (b), (c), and (d); dispersing the NCO prepolymer in water, with at least partial neutralization of the ionic groups taking place before, during, or after dispersion; chain extending the NCO prepolymer with component (e); and distilling the resulting dispersion to remove the solvent. Provided that, component (f) is used in the first step, or component (g) in the third step.