Aqueous Ink Formulation for Intermittent Ejection Stability
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Solution Overview
Problem
Ink jet recording methods using line-type recording heads face challenges with intermittent ejection stability due to ink viscosity increases and adhesion issues, leading to unstable ejection and potential image quality disturbances, especially when the recording head is not in use for extended periods.
Innovation Solution
An aqueous ink formulation containing a surfactant with a low HLB value, a poorly water-soluble solvent A, and a highly water-soluble solvent B, where solvent A has a solubility of 5.00 g/100g-H2O or less and a vapor pressure of 0.5 mmHg or less, and solvent B has a partition coefficient within the range of 1.44 Log P A - 0.1x - 3.4 ≤ Log P B ≤ -0.6, to prevent water evaporation and maintain ejection stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If water is used as the main solvent in aqueous ink, then the ink provides good color quality and ease of manufacture, but water evaporates from ejection openings during idle periods causing viscosity increase and ejection failure
Solution Approach 1:
The patent uses a composite solvent system combining water with a poorly water-soluble organic solvent (having specific solubility and vapor pressure characteristics). This composite approach maintains the benefits of water-based ink while adding a component that forms a protective film to prevent evaporation during idle periods, thereby resolving the contradiction between ease of manufacture and intermittent ejection stability.
2Ease of operation
If a surfactant with low HLB value is used to improve wettability and ejection performance, then the ink achieves better ejection characteristics, but the ink becomes more susceptible to evaporation and viscosity increase during idle periods
Solution Approach 1:
The patent combines a low HLB value surfactant with a poorly water-soluble organic solvent in specific proportions. The surfactant provides excellent ejection characteristics and wettability, while the organic solvent component forms a protective film that prevents evaporation. This composite formulation resolves the contradiction between ease of operation and reliability by making each component compensate for the other's weaknesses.
3Loss of energy
If the recording head is left idle for extended periods, then energy consumption is reduced and operational cost decreases, but water evaporation causes ink viscosity increase and adhesion to nozzles leading to ejection failure
Solution Approach 1:
The patent incorporates a poorly water-soluble organic solvent that proactively forms a protective film on the ink and nozzle surfaces during idle periods. This preliminary protective action prevents water evaporation and ink adhesion before they can cause viscosity increase or ejection failure, allowing the recording head to remain idle without compromising subsequent ejection 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 ink formulation ensures stable ink ejection over extended periods by preventing water evaporation and viscosity increases, enhancing intermittent ejection stability and maintaining image quality even in conditions where water evaporates easily.
Implementation Method 1
the solvent A includes an alcohol having a vapor pressure at 20°C of 0.5 mmHg or less... to prevent water evaporation and maintain ejection stability
Implementation Method 2
a surfactant having an HLB value of 9.0 or less... to ensure stable ink ejection over extended periods
Implementation Method 3
the solvent A includes an alcohol having a vapor pressure at 20°C of 0.5 mmHg or less... to prevent water evaporation and viscosity increases
Data Source
Figure 1
Figure 2~3
AI summary
An aqueous ink for ink jet includes a coloring material, a solvent, and a surfactant having an HLB value of 9.0 or less. The solvent includes a solvent A having a solubility in water at 20°C of 5.00 g/100g-H2O or less and a solvent B other than the solvent A. The solvent A includes an alcohol having a vapor pressure at 20°C of 0.5 mmHg or less and a surface tension of 30.0 mN/m or more. The content of the alcohol in the aqueous ink is 0.7 or more times the solubility in water at 20°C in an equal amount to the aqueous ink. The solvent B has a partition coefficient (PB) satisfying the following equation (1). 1.44LogPA−0.1x−3.4≤LogPB≤−0.6