Cationic Polyurethane Dispersion for pH-Stable Inkjet Fixation
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Solution Overview
Problem
Existing aqueous cationic polyurethane dispersions face issues with pH-dependent cationic character loss, require toxic quaternization reagents, and necessitate high-boiling organic solvents, making them difficult to produce solvent-free and stable for inkjet printing applications.
Innovation Solution
Aqueous polyurethane resin dispersion with cationic groups and polyalkylene oxide side chains, synthesized using specific cationic polyols and polyether diols, allowing for pH-independent cationic character and solvent-free production.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If tertiary amino diols or polyols are used to produce aqueous cationic polyurethane dispersions, then the cationic character is pH dependent, but this leads to deprotonation and loss of cationic character when pH increases (e.g., in ink jet printing with neutral or alkaline inks)
Solution Approach 1:
The invention changes the chemical parameter of the cationic group from protonatable tertiary amino groups to permanently charged quaternary ammonium groups. This parameter change ensures the cationic character remains constant across different pH conditions, eliminating deprotonation issues while maintaining reliability in ink jet printing applications with neutral or alkaline inks.
Solution Approach 2:
The quaternization of the amino diol is performed before polyurethane synthesis, incorporating the permanently cationic quaternary ammonium group into the polyol structure from the outset. This preliminary action ensures the cationic character is established and maintained throughout the subsequent polymerization and application processes, preventing pH-dependent loss of functionality.
2Reliability
If quaternized amino diols are used to achieve pH-independent cationic character, then the cationic character is stable, but the solubility in typical polyurethane synthesis solvents (acetone, acetonitrile, dioxalane) is poor, requiring high-boiling solvents that are difficult to remove
Solution Approach 1:
The invention modifies the molecular structure parameter of the quaternized amino diol by extending the carbon chain length between the cationic charged atom and the hetero atom or chain end to at least 12 carbon atoms. This structural parameter change reduces the strength of ion-dipole interactions with solvent molecules, improving solubility in low-boiling solvents like acetone and acetonitrile, thereby facilitating easier solvent removal while maintaining pH-independent cationic stability.
3Reliability
If quaternization is performed after polyurethane synthesis (as disclosed in US3686108 and US7964665B2), then pH-independent cationic character is achieved, but toxic reagents (methyl sulphate, benzyl chloride) must be used and incomplete quaternization requires removal of residual reagents
Solution Approach 1:
The invention performs quaternization of the amino diol before polyurethane synthesis, incorporating the quaternary ammonium group into the polyol structure from the beginning. This preliminary action eliminates the need for post-synthesis quaternization steps, avoiding the use of toxic reagents like methyl sulphate and benzyl chloride, and preventing residual reagent contamination in the final product.
Solution Approach 2:
The invention uses readily available, non-toxic quaternized amino diols as starting materials that can be purchased commercially or synthesized using safe reagents. This approach replaces the need for expensive and toxic post-synthesis quaternization reagents, making the process safer and more environmentally friendly while achieving the same pH-independent cationic functionality.
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 solution provides stable, solvent-free polyurethane dispersions with enhanced colorant fixation power and improved scratch resistance, suitable for inkjet printing without the need for high-boiling solvents or toxic reagents.
Implementation Method 1
reacting a polyisocyanate with a polyether diol, with a polymeric diol and with a cationic polyol
Implementation Method 2
fixing the colorants of the inks applied subsequently onto the substrate
Data Source
AI summary
An aqueous polyurethane resin dispersion, the polyurethane resin having a cationic group and a polyalkylene oxide in a side chain thereof and is obtainable by reacting a polyisocyanate with a polyether diol and with a polymeric diol such as a polyester diol, polyether diol, polycarbonate diol, polyacrylate diol or polyolefin diol and with a cationic polyol selected from the group consisting of an quaternary ammonium, a quaternary phosphonium, a tertiary sulfonium and a iodonium wherein the cationic polyol comprises at least two hydroxyl groups and has a total number of carbon atoms making up the carbon chains between the cationic charged atom and a hetero atom or end of the carbon chain of the cation over charge ratio of at least 12. The aqueous dispersion can be used in treatment liquids for inkjet printing and in inkjet inks.