Wetness Sensor Ink Using Aliphatic Carboxylic Acid for Rapid Color Change
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Solution Overview
Problem
Existing wetness sensors in disposable absorbent articles are insensitive to small amounts of bodily fluids, require surfactants increasing costs and complexity, and take a long time to undergo color change, making them ineffective for real-time wetness detection.
Innovation Solution
A wetness sensor integrated into absorbent articles using an ink comprising a proton-accepting chromogen and a proton-donating agent, specifically an aliphatic carboxylic acid, which undergoes rapid visible color change upon contact with bodily fluids, ensuring timely detection of wetness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional leuco dye and color developer sensors are used, then visual signal is provided in dry state, but the sensor requires surfactants which increases costs and complexity
Solution Approach 1:
The patent removes the surfactant component from the sensor system entirely. The ink composition uses a proton-accepting chromogen and proton-donating agent that function without requiring surfactants, thereby reducing device complexity and cost while maintaining reliable visual signaling through the color change mechanism.
Solution Approach 2:
The patent changes the chemical parameters of the sensor system by selecting specific proton-accepting chromogens and proton-donating agents with appropriate pKa values. This parameter optimization allows the sensor to function effectively without surfactants, resolving the contradiction between reliability and complexity.
2Reliability
If traditional wetness sensors are used, then color change occurs upon wetting, but the color change takes a long time making them ineffective for real-time detection
Solution Approach 1:
The patent optimizes the chemical parameters of the ink composition, specifically selecting proton-donating agents with pKa values between 3-7 and proton-accepting chromogens with appropriate basicity. These parameter changes accelerate the color change kinetics, enabling real-time wetness detection within seconds while maintaining reliable detection across various wetness levels.
Solution Approach 2:
The patent creates a composite ink system combining specific proton-accepting chromogens with proton-donating agents. This composite material formulation enhances the speed of color change response while maintaining detection reliability, resolving the time delay issue in traditional sensors.
3Measurement precision
If traditional sensors are used, then wetness detection is provided, but the sensors are insensitive to small amounts of bodily fluids
Solution Approach 1:
The patent enhances the local quality of the sensor by concentrating the proton-accepting chromogen and proton-donating agent in the ink composition at optimized ratios. This local concentration increase improves the sensor's sensitivity to small amounts of bodily fluids, enabling detection of even minor wetness events while maintaining overall detection precision.
Solution Approach 2:
The patent adjusts the chemical parameters of the ink composition, including the concentration and pKa values of the proton-donating agent and the basicity of the proton-accepting chromogen. These parameter changes increase the sensor's sensitivity to trace amounts of fluid, resolving the contradiction between measurement precision and fluid quantity detection.
4Ease of operation
If surfactants are added to achieve sufficient wetting, then wetness detection is improved, but costs and complexity increase
Solution Approach 1:
The patent extracts and eliminates the surfactant component from the sensor system. The ink composition relies on the inherent properties of the proton-accepting chromogen and proton-donating agent to achieve sufficient wetting and color change, thereby simplifying the device while maintaining ease of operation for wetness detection.
Solution Approach 2:
The sensor system performs self-service by using the proton-donating agent and proton-accepting chromogen to achieve both wetting and color change functions without external surfactant assistance. This self-sufficient design reduces complexity while maintaining ease of operation.
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 sensor provides a rapid and reliable visual indication of wetness, allowing for real-time detection within seconds, improving user awareness and reducing the need for surfactants, thus enhancing the effectiveness and efficiency of wetness sensing.
Implementation Method 1
the chromogen is colorless prior to use in its protonated form. However, upon contact with bodily fluids (e.g., urine, fecal matter, mucus, menses, vaginal fluid, etc.), water in the fluid can lead to deprotonation of the chromogen, thereby resulting in a shift of the absorption maxima
Implementation Method 2
The ink includes a proton-accepting chromogen and a proton-donating agent. The proton-donating agent is an aliphatic carboxylic acid that is highly soluble in the bodily fluid
Data Source
AI summary
A wetness sensor for an absorbent article that is formed from an ink is provided. The ink includes a proton-accepting chromogen and a proton-donating agent (or color developer). Prior to use, the ink is generally dry and in a protonated form so that it has a visible color. However, upon contact with bodily fluids (e.g., urine, fecal matter, mucus, menses, vaginal fluid, etc.), water in the fluid can lead to deprotonation of the chromogen, thereby resulting in a shift of the absorption maxima of the chromogen towards either the red (“bathochromic shift”) or blue end of the spectrum (“hypsochromic shift”). To increase the rate of the color change during use, the proton-donating agent is an aliphatic carboxylic acid that is highly soluble in the bodily fluid (e.g., urine), and therefore results in a color change that is very rapid and may be detected within a relatively short period of time.