Erasable Non-Aqueous Ink With pH-Sensitive Dye
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Solution Overview
Problem
Existing non-aqueous solvent-based inks for ballpoint pens face challenges in achieving a balance between smooth writing, preventing leakage, and maintaining color intensity, especially when incorporating erasable or color-changing properties, due to high shear viscosity and compatibility issues with water-based systems.
Innovation Solution
A non-aqueous writing ink comprising a solvent such as 1,2-propanediol, diethylene glycol, or dimethylsulfoxide, combined with a pH-sensitive water-soluble dye and a gelling agent like water-insoluble cellulose nanofibers or silica particles, which changes color in response to a pH increase, allowing for high laydown without leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high shear viscosity is used in non-aqueous solvent-based inks, then leakage is prevented and shelf-life is extended, but writing smoothness deteriorates and the ink feels heavy-handed
Solution Approach 1:
The patent changes the rheological parameters of the ink by introducing a pseudoplastic ink composition with specific viscosity characteristics. The ink has a viscosity of at least 20 Pa·s at 0.1 s⁻¹ shear rate but decreases under writing conditions, enabling both leakage prevention and smooth writing. This parameter optimization resolves the contradiction between high viscosity for leakage prevention and low viscosity for writing smoothness.
Solution Approach 2:
The patent employs a dynamic rheological system where the ink viscosity adapts to shear conditions. The pseudoplastic behavior allows the ink to maintain high viscosity at rest (preventing leakage) while automatically reducing viscosity during writing (improving smoothness). This dynamic adjustment resolves the static contradiction between leakage prevention and writing ease.
2Ease of operation
If water-based gel inks are used, then writing smoothness and particle stabilization improve, but cap-off time decreases and corrosion issues arise requiring expensive stainless steel points
Solution Approach 1:
The patent applies local quality by using a non-aqueous solvent system (ethyl acetate, isopropyl alcohol) instead of water, eliminating corrosion issues while maintaining smooth writing through pseudoplastic rheology. This allows the use of cheaper brass points instead of expensive stainless steel, resolving the contradiction between writing smoothness and manufacturing cost.
Solution Approach 2:
The patent changes the chemical composition parameters from water-based to non-aqueous solvent-based gel ink, achieving both writing smoothness and corrosion resistance. The specific solvent mixture and gelling agent combination maintains the desired rheological properties without the corrosivity of water, eliminating the need for expensive stainless steel points.
3Duration of action of stationary object
If conventional non-aqueous solvent-based inks are used, then shelf-life is extended, but writing smoothness deteriorates due to high shear viscosity
Solution Approach 1:
The patent introduces dynamic rheological behavior where the ink viscosity automatically adjusts based on shear rate. During storage, the ink maintains high viscosity for stability and leakage prevention. During writing, the shear force causes viscosity reduction for smooth flow. This dynamic adaptation resolves the contradiction between shelf-life and writing smoothness.
Solution Approach 2:
The patent optimizes the viscosity parameters of the non-aqueous solvent-based ink by incorporating specific gelling agents and solvent ratios. The ink achieves a viscosity profile where rest viscosity ensures shelf stability while shear-thinning behavior enables smooth writing, resolving the contradiction between extended shelf-life and writing smoothness.
4Adaptability or versatility
If pH-sensitive water-soluble dyes are used for color-change properties, then erasability improves, but compatibility with non-aqueous solvent systems deteriorates
Solution Approach 1:
The patent uses pH-sensitive water-soluble dyes as intermediaries that respond to the alkaline eradicator composition. The dyes are incorporated into the non-aqueous ink system through careful formulation, allowing them to remain soluble and responsive while maintaining compatibility with the solvent-based ink matrix. This enables erasability without compromising ink system stability.
Solution Approach 2:
The patent selects specific pH-sensitive dyes and adjusts the ink formulation parameters to ensure dye solubility and responsiveness in the non-aqueous solvent system. The dye concentration, solvent composition, and pH buffer system are optimized to maintain dye stability in the ink while enabling effective color change upon exposure to the alkaline eradicator, resolving the contradiction between erasability and system compatibility.
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 provides a smooth writing experience with high laydown and vivid color intensity, while preventing leakage and enabling effective color change or erasure without smearing, suitable for use in high laydown writing instruments.
Implementation Method 1
The pH-sensitive water-soluble dye is capable of changing from an initially colored state to a discolored state when the writing ink is exposed to an ink eradicator composition or a pH-change, more specifically a pH increase
Data Source
AI summary
The present disclosure relates to a eradicable non-aqueous writing ink comprising a solvent, a gelling agent and a pH-sensitive water-soluble dye. The solvent is selected from 1,2-propanediol, diethylene glycol, monoethylene glycol and dimethylsulfoxide and/or mixtures thereof. The gelling agent comprises water-insoluble cellulose nanofibers and/or a mixture of silica particles and of a fatty acid amide wax. The pH-sensitive water-soluble dye is capable of changing from an initially colored state to a discolored state when the writing ink is exposed to an ink eradicator composition.