Cross-linked Polyurethane Dispersants for Stable Pigment Inks
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Solution Overview
Problem
Current polyurethane dispersants used in ink-jet printing fail to provide stable, durable, and high-quality inks with adequate stability, durability, optical density, and chroma, particularly in ink-jet applications, where pigment dispersions tend to agglomerate or flocculate during storage and use.
Innovation Solution
Development of cross-linked polyurethane dispersants with cross-linkable moieties pendent to the polymer backbone and dispersing moieties both pendant and terminal to the polymer chain, which are cross-linked with specific agents like epoxide, isocyanate, or carbodiimide, enhancing the stability and performance of aqueous pigment dispersions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If conventional polyurethane dispersants are used in ink-jet printing, then the ink can be formulated and applied, but the pigment dispersion becomes unstable and tends to agglomerate or flocculate during storage and use
Solution Approach 1:
The patent uses composite dispersant systems combining polyurethane backbone structures with grafted polyalkylene oxide side chains and terminal hydrophilic groups. This composite structure provides both strong pigment binding (via polyurethane) and enhanced steric stabilization (via flexible polyether chains and terminal hydrophilic groups), preventing pigment agglomeration and flocculation while maintaining dispersion stability during storage and jetting cycles.
Solution Approach 2:
The patent modifies the chemical structure of polyurethane dispersants by incorporating cross-linkable moieties (such as carboxyl, hydroxyl, or amine groups) that can form cross-linked networks. This parameter change transforms the linear polymer structure into a three-dimensional cross-linked structure, significantly enhancing the dispersant's ability to stabilize pigment particles and prevent agglomeration under varying pH, temperature, and storage conditions.
2Ease of operation
If pigment is dispersed in aqueous vehicle using conventional dispersants, then the ink can be formulated, but the pigment particles agglomerate or flocculate during storage and jetting cycles
Solution Approach 1:
The patent introduces local quality variations in the dispersant structure by placing different functional groups at specific locations: the polyurethane backbone provides rigid pigment surface binding, while flexible polyalkylene oxide side chains provide steric barrier, and terminal hydrophilic groups (such as carboxyl, sulfonate, or phosphate) provide electrostatic repulsion and water solubility. This localized functional distribution optimizes both ease of formulation and long-term dispersion stability.
Solution Approach 2:
The dispersant molecule is segmented into distinct functional domains: a polyurethane backbone segment for strong adsorption to pigment surfaces, polyalkylene oxide side chain segments for steric stabilization, and terminal hydrophilic group segments for electrostatic repulsion and aqueous solubility. This segmentation allows each segment to perform its specific function, preventing pigment agglomeration while maintaining ease of ink formulation.
3Ease of manufacture
If standard polyurethane dispersants are used, then the ink can be produced, but the ink lacks sufficient durability, rub-fastness, wet-fastness, and highlighter pen fastness
Solution Approach 1:
The patent incorporates cross-linkable moieties in the dispersant structure that can form cross-linked networks during or after ink formulation. This preliminary incorporation of cross-linking capability allows the dispersant to provide immediate stabilization during formulation while the subsequent cross-linking process (triggered by pH adjustment, heat, or time) enhances durability, rub-fastness, wet-fastness, and highlighter pen fastness, ensuring both ease of manufacture and superior ink performance.
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 cross-linked polyurethane dispersants result in highly stable and durable ink-jet inks with improved stability, rub-fastness, wet-fastness, and highlighter pen fastness, maintaining performance throughout repeated jetting cycles and storage.
Implementation Method 1
the cross-linking of the cross-linkable moieties with a cross-linking agent
Data Source
AI summary
The present disclosure provides an aqueous dispersion containing a colorant and a polyurethane dispersant, wherein the polyurethane dispersant is a polymer having a cross-linkable moiety, wherein the cross-linkable moiety is cross-linked with a cross-linking agent.