Stretchable Polymer Thick Film Circuits for Washable Wearables
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Solution Overview
Problem
Conductive polymer thick film circuits face challenges in maintaining conductivity and integrity when subjected to significant stretching and multiple wash and dry cycles, particularly in wearable garment applications, where traditional substrates like polyester and polycarbonate are not suitable.
Innovation Solution
A polymer thick film composition comprising 20-92 wt% electrically conductive metal powder or silver powder with silver chloride, combined with an organic medium of 5-50 wt% thermoplastic polyurethane resin, which has a high elongation percentage and low tensile stress, is used to form a conductor layer that can be stretched and maintained after wash and dry cycles, and an encapsulant layer with fumed silica is applied to protect the circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional substrates like polyester and polycarbonate are used for conductive polymer thick film circuits, then manufacturing is straightforward, but the circuits cannot withstand significant stretching and maintain conductivity in wearable applications
Solution Approach 1:
The patent changes the substrate material parameters by using thermoplastic polyurethane (TPU) instead of traditional polyester or polycarbonate substrates. This parameter change enables the substrate to achieve high elongation (at least 200%) while maintaining mechanical integrity and electrical conductivity through the integrated PTF composition, making it suitable for wearable applications requiring significant stretching.
Solution Approach 2:
The patent creates a composite material system where the PTF composition (containing conductive metal particles) is integrated with the TPU substrate. This composite structure combines the electrical conductivity of metal particles with the high elasticity and mechanical properties of TPU, achieving both conductivity maintenance during stretching and adaptability for wearable applications.
2Shape
If the polymer thick film composition uses high elastomer content for stretchability, then elongation capability improves, but the composition becomes too soft and loses structural integrity
Solution Approach 1:
The patent optimizes the elastomer content parameter within a specific range (5-50 wt% of the organic medium) to achieve the desired balance. This parameter change ensures sufficient elongation capability (at least 200%) while maintaining structural integrity through the synergistic combination of elastomer and resin components in the composition.
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 composition maintains conductivity and integrity through high elongation and low resistance change after repeated stretching and washing, making it suitable for wearable electronics applications.
Implementation Method 1
an organic medium comprising 5-50 wt% thermoplastic polyurethane resin dissolved in an organic solvent
Implementation Method 2
wherein the composition is dried to remove said solvent and form said conductor
Implementation Method 3
the thermoplastic polyurethane having a per cent elongation of at least 200% and a tensile stress necessary to achieve 100% elongation of less than 1000 psi
Data Source
AI summary
This invention is directed to stretchable polymer thick film compositions useful for wearable garments. More specifically, the polymer thick film may be used in applications where significant stretching is required, particularly on substrates that can be highly elongated. A particular type of substrate is a thermoplastic polyurethane substrate.