Carboxyl Polyurethane Ink for Stable Ejection and Scratch Resistance
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Solution Overview
Problem
Aqueous inkjet inks using pigments face challenges with ejection stability and image quality, particularly on glossy papers, due to random introduction of carboxyl groups in polyurethane chains, leading to heterogeneous molecular structures and reduced water solubility, which affects discharge properties and scratch resistance.
Innovation Solution
A carboxyl group-containing polyurethane is synthesized with controlled carboxyl group introduction, maintaining a reaction index between 0.95 and 1.10, ensuring homogeneous distribution and preventing crosslinking, thereby stabilizing the ink's ejection and enhancing scratch resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a carboxyl group-containing polyurethane is used to improve fixation and scratch resistance, then the scratch resistance and fixation are improved, but the ejection stability deteriorates due to heterogeneous molecular structure and reduced water solubility
Solution Approach 1:
The invention controls the reaction index (molar ratio of diisocyanate to diol) within a specific range of 0.95-1.10 to achieve homogeneous carboxyl group distribution in the polyurethane chain. This parameter control prevents random crosslinking and maintains water solubility, thereby preserving ejection stability while achieving improved scratch resistance through controlled carboxyl group content (20-70 mg KOH/g).
Solution Approach 2:
The invention introduces carboxyl groups at specific locations along the polyurethane chain by controlling the reaction between diisocyanate and diol compounds. This localized introduction of carboxyl groups at controlled intervals provides scratch resistance and fixation properties without creating heterogeneous molecular structures that would compromise ejection stability.
2Reliability
If pigment particles are dispersed in aqueous solvent to create pigment ink, then weather resistance and light resistance are improved, but the color development and gloss are impaired due to diffuse reflection by pigment particles
Solution Approach 1:
The invention creates a composite system by dispersing pigment particles within a carboxyl group-containing polyurethane matrix in controlled aqueous dispersion. The polyurethane binder forms a continuous film that binds pigment particles together, reducing light scattering at particle interfaces and improving gloss while maintaining the weather and light resistance provided by the pigment particles.
3Strength
If resin component is added to improve fixation onto recording medium, then fixation is improved, but the ejection stability and gloss properties deteriorate
Solution Approach 1:
The invention optimizes the molecular structure parameters of the polyurethane resin by controlling the reaction index and selecting specific diol compounds (including carboxyl-containing diols). This produces a resin with balanced properties: sufficient molecular weight and functional groups for fixation (20-70 mg KOH/g acid value), while maintaining water solubility and low viscosity for stable ejection.
4Ease of manufacture
If thermal system is used to discharge ink droplets, then printing process is simplified, but cogation occurs in heater portion due to rapid temperature change, causing discharge failure
Solution Approach 1:
The invention modifies the ink's physical parameters by incorporating carboxyl group-containing polyurethane, which adjusts the ink's viscosity, surface tension, and thermal response characteristics. These parameter changes enable the ink to withstand rapid heating and cooling cycles in thermal inkjet systems without causing cogation, maintaining stable discharge over prolonged printing processes.
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 ink droplet discharge and improved scratch resistance, with superior ejection stability and image quality on glossy papers, maintaining high print density and gloss values even after multiple prints.
Implementation Method 1
a carboxyl group-containing polyurethane, which is formed by reacting a diol compound (C) and a reaction product, which is mainly composed of a compound represented by general formula (1) and prepared by reacting a dial compound (A) having one or two carboxyl groups within each molecule with a diisocyanate compound (B)
Implementation Method 2
An aqueous pigment ink is usually a pigment dispersion prepared by homogeneously dispersing pigment particles in an aqueous solvent such as water
Implementation Method 3
since the ink inside the nozzle is boiled with a heater constituted of the heat elements provided in the printer head to discharge the ink droplets
Implementation Method 4
the ink inside the nozzle is boiled with a heater constituted of the heat elements provided in the printer head to discharge the ink droplets
Implementation Method 5
carboxyl groups are homogeneously introduced within the polymer chain of the polyurethane
Data Source
AI summary
There is provided a pigment dispersion including water, an aqueous polymer and a pigment as essential components,wherein the aqueous polymer is a carboxyl group-containing polyurethane which is formed by reacting a diol compound, a diisocyanate compound and a reaction product, which is mainly composed of a compound represented by general formula (1) and prepared by reacting a diol compound having one or two carboxyl groups within each molecule with a diisocyanate compound and which also has a reaction index as calculated by (Formula 1) within a range from 0.95 to 1.10.Reaction index=(reaction rate of isocyanate group)×[(number of moles of diisocyanate compound(B))/(number of moles of diol compound(A))] (Formula 1)