Aqueous Ink Pigment Stabilization via Urethane Resin and Surfactant
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Solution Overview
Problem
Current aqueous inkjet recording methods using pigment inks face challenges in achieving high color reproducibility and light fastness, particularly with quinacridone-based pigments, which have weak coloring power and low light fastness, and naphthol AS-based azo pigments, which discolor over time, while also experiencing issues with intermittent ejection stability due to aggregate formation in the recording head.
Innovation Solution
An aqueous ink formulation incorporating a naphthol AS-based azo pigment, a quinacridone-based pigment, and a water-soluble urethane resin, along with a silicone-based surfactant, to enhance color developability, light fastness, and intermittent ejection stability by controlling the interactions between these components and preventing aggregate formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If naphthol AS-based azo pigment is used to improve color developability, then coloring power increases, but light fastness deteriorates causing image discoloration
Solution Approach 1:
The patent introduces a specific urethane resin as an intermediary substance that binds to the naphthol AS-based azo pigment particles. This resin coating acts as a protective layer that prevents direct light exposure to the pigment, thereby maintaining light fastness while preserving the high coloring power of the azo pigment. The resin serves as a mediator between the pigment and the environment.
Solution Approach 2:
The patent creates a composite pigment structure by combining naphthol AS-based azo pigment with quinacridone-based pigment and coating them with urethane resin. This composite approach allows the system to achieve both high coloring power from the azo pigment and improved light fastness from the protective resin coating and complementary quinacridone pigment.
2Reliability
If quinacridone-based pigment is used to improve light fastness, then image stability increases, but coloring power decreases
Solution Approach 1:
The patent merges two different pigment types - naphthol AS-based azo pigment (high coloring power) and quinacridone-based pigment (good light fastness) - into a single ink formulation. This combination allows the system to achieve both high coloring power and adequate light fastness by leveraging the strengths of each pigment type.
3Quantity of substance
If pigment concentration is increased to improve color reproducibility, then color developability increases, but aggregate formation occurs causing intermittent ejection instability
Solution Approach 1:
The patent introduces a dispersant as an intermediary substance that mediates between pigment particles and the aqueous medium. This dispersant prevents pigment aggregation even at high concentrations by maintaining particle separation through steric or electrostatic repulsion, thereby enabling high color reproducibility without compromising ejection stability.
Solution Approach 2:
The patent optimizes the particle size distribution and surface properties of the pigments to prevent aggregation. By controlling particle size parameters and surface charge characteristics, the system achieves stable dispersion at high pigment concentrations, maintaining both color reproducibility and intermittent ejection stability.
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 ink achieves satisfactory color developability, light fastness, and intermittent ejection stability, ensuring consistent ejection accuracy and reducing disturbances in image recording by stabilizing the dispersed state of pigments and preventing aggregate formation in the recording head.
Implementation Method 1
the silicone-based surfactant is at least one kind selected from the group consisting of compounds represented by the following respective general formulae (1) to (3), has a weight-average molecular weight of 800 or more to 10,000 or less and has an HLB value measured by Griffin's method of 4 or more
Implementation Method 2
a water-soluble urethane resin having a unit derived from a polyisocyanate, a unit derived from a polyol having no acid group and a unit derived from a polyol having an acid group
Data Source
AI summary
Provided is an aqueous ink for ink jet including: pigments; a urethane resin; and a silicone-based surfactant. The pigments include a first pigment and a second pigment, the first pigment is a naphthol AS-based azo pigment and the second pigment is a quinacridone-based pigment. The urethane resin is a water-soluble urethane resin having a unit derived from a polyisocyanate, a unit derived from a polyol having no acid group and a unit derived from a polyol having an acid group. The silicone-based surfactant is at least one kind selected from the group consisting of compounds represented by the following respective general formulae (1) to (3), has a weight-average molecular weight of 800 or more to 10,000 or less and has an HLB value measured by Griffin's method of 4 or more.