Urethane Prepolymer Adhesive for Wearable Devices
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Solution Overview
Problem
Pressure-sensitive adhesives for skin applications require excellent moisture permeability, but existing adhesives often have high adhesion to both skin and substrates, leading to skin damage when removed.
Innovation Solution
A hydroxy group-terminated polyurethane prepolymer is developed by reacting oxyalkylene polymers with specific molecular weights and ethylene oxide unit contents, along with a diisocyanate compound, to create an adhesive with low skin adhesion and high substrate adhesion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the adhesive has high adhesion to both skin and substrate, then the attachment strength is improved, but the skin may be damaged when removing the adhesive
Solution Approach 1:
The adhesive composition is designed with different functional components that create local differences in adhesion properties. The polyol mixture containing both high molecular weight (≥5,000) and low molecular weight (1,500-5,000) components creates regions with different adhesion characteristics, allowing strong substrate bonding while maintaining gentle skin release
Solution Approach 2:
The adhesive uses a composite polyol system combining polyoxyalkylene polymers with different molecular weights and functional group counts. This composite structure enables the adhesive to exhibit dual adhesion behavior: strong bonding to substrates through certain components while providing gentle detachment from skin through other components
2Reliability
If the adhesive has excellent moisture permeability, then moisture evaporation is improved, but the adhesion performance may be compromised
Solution Approach 1:
The adhesive optimizes the molecular weight parameters of the polyol components. By setting the number average molecular weight of polyol (2) at ≥5,000 and polyol (3) at 1,500-5,000, the formulation achieves a balance where the higher molecular weight component provides moisture permeability while the lower molecular weight component maintains adhesion strength
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 resulting adhesive exhibits excellent moisture permeability, low adhesion to skin, and high adhesion to substrates, preventing skin damage during removal and ensuring effective attachment of wearable devices.
Implementation Method 1
A hydroxy group-terminated polyurethane prepolymer which is obtained by reacting an oxyalkylene polymer A having an average number of hydroxy groups per molecule of from 2.1 to 3, an oxyalkylene polymer B having one hydroxy group per molecule, and a diisocyanate compound
Implementation Method 2
Pressure-sensitive adhesives to be applied to skin are required to have excellent moisture permeability so that when used as a pressure-sensitive adhesive layer of an adhesive skin patch, moisture due to sweating from the skin would evaporate to outside of the adhesive skin patch
Data Source
AI summary
Provided are a urethane prepolymer from which is obtained an adhesive which has excellent moisture permeability and which attains both low adhesion to skin and high adhesion to a base material, an adhesive, a skin patch material, an adhesive tape, a wearable device, and a wearable device kit. The urethane prepolymer is a hydroxyl-group-terminated urethane prepolymer obtained by reacting an oxyalkylene polymer A having an average number of hydroxyl groups per molecule of 2.1 to 3, an oxyalkylene polymer B in which the number of hydroxyl groups per molecule is 1, and a diisocyanate compound, the number-average molecular weight of the oxyalkylene polymer B being 5000 or greater, and the content of ethylene oxide units in the hydroxyl-group-terminated urethane prepolymer being more than 10 mass %.