Stretchable Conductive Paste for Wearable Electronics
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Solution Overview
Problem
Conductive pastes used in stretchable electronic devices face issues with resistance increase and durability when subjected to repeated stretching, particularly with narrow wiring widths, due to insufficient crosslinking and heat resistance limitations in existing binder materials.
Innovation Solution
A conductive paste composition incorporating a polyurethane elastomer with a specific urethane group concentration and glass transition temperature, combined with silver particles and carbon materials, which allows for high repeated stretchability without the need for crosslinking agents and maintains conductivity even after extensive elongation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a metal wire or metal foil is used to form an electrical wiring line, then the conductivity is high, but the stretchability is insufficient
Solution Approach 1:
The patent changes the physical state and composition parameters by replacing traditional metal conductors with a conductive paste containing conductive particles (silver, carbon, etc.) dispersed in a specific binder resin system. This transformation enables the wiring line to achieve both high conductivity and stretchability by allowing the conductive particles to maintain electrical contact while the binder accommodates deformation.
Solution Approach 2:
The patent creates a composite material system consisting of conductive particles (silver powder, carbon black, or carbon nanotubes) combined with a specially formulated binder resin (polyurethane or silicone rubber with specific molecular weight and glass transition temperature). This composite structure combines the electrical conductivity of metal particles with the elasticity of polymer binders, resolving the contradiction between conductivity and stretchability.
2Adaptability or versatility
If a corrugated wiring line is formed by placing metal wire or metal foil in a corrugated shape, then pseudo stretchability is achieved, but permanent plastic deformation occurs under excessive deformation
Solution Approach 1:
The patent changes the structural parameters by abandoning the corrugated geometry in favor of a smooth wiring line formed from conductive paste. The key parameter change is in the material composition - using a binder resin with specific glass transition temperature and molecular weight that provides inherent elasticity, allowing the wiring to stretch and recover without permanent deformation.
Solution Approach 2:
The patent replaces the durable but non-stretchable metal foil with a consumable conductive paste formulation that can be printed and cured to form a stretchable wiring line. This approach sacrifices the indefinite durability of metal but gains stretchability and durability under repeated deformation through the optimized polymer matrix.
3Productivity
If the wiring width is reduced to 5 mm or less for device miniaturization, then the device size is reduced, but the resistance increase becomes significant during repeated stretching
Solution Approach 1:
The patent optimizes multiple parameters including the binder resin molecular weight (10,000-1,000,000), glass transition temperature (-60°C to 0°C), and conductive particle concentration to achieve narrow wiring widths (5 mm or less) while maintaining stable resistance. The specific parameter range of the binder resin ensures sufficient elasticity and particle contact maintenance even in narrow wiring configurations.
Solution Approach 2:
The patent applies local quality optimization by ensuring uniform distribution of conductive particles within the binder resin matrix, creating consistent electrical properties throughout the narrow wiring line. The localized interaction between conductive particles and binder resin molecules ensures stable electrical contact at each point along the narrow wiring path.
4Adaptability or versatility
If existing conductive paste compositions are used, then the wiring line has stretchability, but the resistance increases significantly after repeated stretching due to insufficient crosslinking
Solution Approach 1:
The patent optimizes the chemical composition parameters of the binder resin, specifically selecting polyurethane or silicone rubber with controlled molecular weight (10,000-1,000,000) and glass transition temperature (-60°C to 0°C). These parameter specifications ensure sufficient crosslinking density and molecular chain flexibility, maintaining both stretchability and resistance stability after repeated deformation cycles.
Solution Approach 2:
The patent creates an optimized composite material system where the binder resin (polyurethane or silicone rubber) forms a crosslinked network that entraps conductive particles. This composite structure provides both the elasticity needed for stretching and the structural integrity to maintain particle contact and conductivity during repeated deformation, resolving the durability issue of existing formulations.
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 solution enables the formation of stretchable conductive lines with reduced resistance increase and improved durability, suitable for wearable devices, by maintaining strong interactions between silver particles and the binder while allowing for fine line printing and high repeated stretchability without crosslinking, thus enhancing the usability of stretchable electronic components.
Implementation Method 1
maintaining strong interactions between silver particles and the binder
Implementation Method 2
a stretchable conductor capable of forming an electric conductor having stretchability... elastomers such as stretchable urethane resin, natural rubber, synthetic rubber
Data Source
AI summary
A stretchable conductor forming paste containing a conductive filler, a polyurethane elastomer having a glass transition temperature (Tg) of −60° C. to −10° C. and a urethane group concentration of 3000 to 4500 m equivalent/kg, and an organic solvent. Preferably, a total amount of components excluding the solvent is 100 parts by mass, a total of the conductive filler is 70 to 95 parts by mass, and an amount of the polyurethane elastomer is 5 to 30 parts by mass. The obtained paste is printed or coated and then dried to obtain a stretchable conductor, capable of forming a wiring line having good repeated stretchability.