pH-Sensitive Inkjet Ink for Wetness Indication
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Solution Overview
Problem
Current methods for indicating wetness in hygienic articles, such as diapers, using inkjet printing face challenges in achieving high-resolution, durable, and visually distinct color changes that remain stable and easy to interpret, while also being cost-effective and easily integratable into production lines.
Innovation Solution
A color-changing inkjet ink composition comprising an organic solvent, a binder resin, and a pH-sensitive dye, which changes from a first color to a second color when exposed to water, allowing for single-pass printing on hygienic articles with high visibility and durability, and is compatible with binary array inkjet printers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If hot melt applicators are used to print wetness indicators, then the composition can be applied, but the image resolution is crude and graphics/text are not effectively possible
Solution Approach 1:
The patent replaces the mechanical hot melt applicator system with an inkjet printing system that uses digitally controlled droplet deposition. This substitution enables high-resolution imaging with graphics and text while maintaining ease of manufacture through digital control mechanisms.
2Adaptability or versatility
If flexographic contact printing is used, then wetness indicators can be applied, but digital variable information cannot be delivered and large footprint is required
Solution Approach 1:
The patent replaces the mechanical flexographic contact printing system with a non-contact inkjet printing system. This enables digital variable information to be delivered through digital control of the printing process while reducing the device footprint and eliminating the need for physical contact between the printing mechanism and substrate.
3Reliability
If current ink jet formulations are used, then printing can be performed, but the images wash away and change from darker to lighter color, resulting in muddled appearance
Solution Approach 1:
The patent employs pH-sensitive dyes that change color in response to urine contact, transitioning from a lighter first color to a darker second color. This color change mechanism provides a clear, visually distinct indication of wetness while the binder resin prevents image dissolution, maintaining sharp definition and readability.
Solution Approach 2:
The patent uses a composite ink formulation consisting of pH-sensitive dyes combined with a binder resin. This composite material provides both the color change functionality and the durability needed to prevent image dissolution, resolving the contradiction between image stability and harmful color changes.
4Illumination intensity
If the second image state is made darker for better visibility, then incontinence indication is clearer, but the ink must remain stable in humid environments before wetness event
Solution Approach 1:
The patent utilizes pH-sensitive dyes that remain stable across a range of ambient conditions but undergo a distinct color change when exposed to urine. The binder resin maintains the dye's stability in humid environments while enabling a sharp transition to a darker, more visible state upon wetness detection, thus achieving both visibility and 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 composition provides rapid and visually perceptible color changes from light to dark within minutes, maintaining clarity and stability even under humid conditions, reducing material usage, and enabling efficient integration into existing production lines.
Implementation Method 1
a pH sensitive dye. An image formed by the ink composition changes from a first color to a second color when exposed to water
Data Source
AI summary
An ink jet ink composition includes an organic solvent in an amount between 60% and 95% by weight of the ink composition, a binder resin, a stabilizing agent, which may be provided by the binder resin, and a pH sensitive dye. An image formed by the ink composition changes from a first color to a second color when exposed to water, wherein the first color is different than the second color.