Product Introductions

Applications of PTFE nanofibers forflexible devices
1. Introduction

・Chemical -resistant, climate-resistant, heat-resistant（260℃）,fire-resistant

Valqua has considered various application utilizing

・Safe for humans（non-invasive, clean）

PTFE nanofibers.

・Water-repellent

In this project, we worked with CONNECTEC JAPAN・High electric resistance, low dielectric constantand started from the stage of brainstorming for ideas on

・Flexible material

utilizing PTFE nanofibers. CONNECTEC JAPAN has

・Good air permeability

their proprietary low-temperature application technology

・Resistant to thermal deformationand is experienced in producing flexible devices.
Table1 shows the general properties of PTFE nanofiber

permeability and flexibility of PTFE nanofibers and also

nonwoven fabric. It is a material with porosity of 80 tothe insulating and water-repellent properties of PTFE

90 % and repels water but has permeability. Expandedmaterial to consider the possibilities of PTFE as aPTFE is a material with similar structure andflexible device.

characteristics, but it shrinks significantly when exposed

Winter 2022

Among several of the candidates, we focused on the airAs flexible devices, we assumed uses in healthcare andwearables. Here we introduce a concept model forNo.42

flexible devices that was produced by conducting
technological development that included direct wiringformation on PTFE nanofibers.

2. Characteristics of PTFE nanofibers
First, we will have a general overview of PTFE
nanofibers1）. As a material, PTFE nanofibers have anonwoven fabric structure and are an aggregate ofPTFE fibers with a diameter of approximately 600 to700 nanometers（Figure1）. The fibers consist of 100%PTFE and are produced from PTFE dispersion using a
special electrospinning method.

Figure1
Table1

Structure of PTFE nanofibers

PTFE nanofiber properties（representative values）

PTFE nanofibers have the following features through itsProperties

Value

Basis weight［g/cm2］

16.7

characteristics as PTFE material and having nanofiber

Thickness［um］

56

Volume resistance ［Ω・cm］

1013

Dielectric constant（@6 GHz）

1.14

Water contact angle［°］140

Air permeability［L/min/cm2/psi］

4.3

structure.

16

Applications of PTFE nanofibers for flexible devices

to 260℃, whereas PTFE nanofiber nonwoven fabricbarely shows any thermal shrinking （Figure2）.

Figure4

Example of wiring by jet dispenser

3-2）Microstructure
Figure2 D ifference in thermal shrinking of PTFE nanofiber
nonwoven fabric（left）and ePTFE（Right）

Figure5 and 6 show a cross-section photograph of circuitboards formed by the jet dispenser method. Generally,
the PTFE surface is water-repellent and oil-repellent, and3. Formation of wiring on PTFE nanofibers

it is a material that is difficult to be printed on as
designed by conductive ink. However, as the figure

Winter 20223-1）Wiring formationshows, wiring material is formed and attached at theTo use as a flexible device, we considered using PTFE

designated line widths on the PTFE nanofibers.

nanofibers itself as a circuit board.

Additionally, it can be seen in the enlarged figure, that a

Wiring formation on PTFE nanofiber was conducted byportion of the conductive ink component has entered thethe printing method. In general, as wiring formation

micropores of PTFE nanofibers, thus maintaining

methods for electric circuits, there are several methods:

adhesion with PTFE nanofibers, and no bleeding ofphotolithography method, inkjet printing method, screen

conductive ink is confirmed.

printing method and gravure offset printing method.
This project used the screen-printing method and jetdispenser method.
Control parameters include conductive ink type

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（conductive particle type and diameter, solvent,viscosity）, printing speed, and discharge pressure in thecase of jet dispenser. Optimization of these parameters
made it possible to conduct wiring formation on PTFE
nanofibers.
Figure3 and 4 show examples of printing of circuits
using screen printing and jet dispenser. Both methods
were able to form wiring without any bleeding ofFigure5

Surface of PTFE nanofibers and wiringconductive ink when printed under optimal conditions.

Figure3

Example of wiring by screen printing
Figure617

Enlarged view

Product Introductions3-3）Durability tests

×30.0

In this project, we confirmed the adhesion of
conductive ink with PTFE nanofibers and the change
in electric resistance value using MIT tests.
The sample used this time was an electromyography
sensor that will be mentioned later, and it was used
after circuit formation with line width of 0.5mm,
followed by covering the circuit with insulationmaterial.
The MIT test was conducted using a tester as shownin Figure7. Table2 shows the test conditions（refer toJIS P8115. However, considering the strength ofFigure8 Photograph of the bending section（After 3,000 repeats）

PTFE nanofibers, no load as designated）. Circuit
between the two edges of the electric circuit before
and after the test.
Table2

MIT testing conditions

Parameter

Testing conditions

Test rate

90 cpm135°

Radius of curvature

0.38 mm

Test repeats

3,000 repeats

Load―Winter 2022

Bending angle

Electric resistance value（Ω）

properties were measured as electric resistance

Test repeats

Figure9 Relationship of conductivity change due to MIT test

4. Application to flexible devices
Figure10 shows a photograph of PTFE nanofibers
with various wiring patterns. By using printing
methods, it is possible to form various wiring patterns.

Figure7

MIT tester

As a result of the test, Figure8 shows no sign ofdisconnection at the bending section（red dotted line）.In
addition, Figure9 shows no significant change in electric
resistance value, and this means good electric
conductivity was maintained even after the test.

Figure10

PTFE nanofibers forming various wiring patterns

18No.42Applications of PTFE nanofibers for flexible devices

As an example of a flexible device using PTFE nanofibers

Figure13 shows a trial touch sensor. A capacitancewith wiring patterns, we tried electromyographychange type touch sensor was manufactured as a trial.

sensors and touch sensors.

The sample shown in the figure had variability in theGenerally, electromyography sensors are made of patch-detection sensitivity per matrix, but was confirmed totype electrodes and assumed to be unsuited forhave the basic functionality of a capacitance change typecontinuous use because they do not have air permeability.

touch sensor.

In contrast, sensors that use PTFE nanofibers would

PTFE nanofibers themselves do not have stretchability,

have the characteristics of PTFE itself and be safe forbut they have the ability to follow free-form surfaces of a

medical use, non-invasive, and water-repellent, as well as

certain degree of size, and applications to various input

air permeability that nanofiber structures have.

user interfaces including wearables can be considered.

Therefore, it would be unlikely that they have anUSB input

adverse effect on the body even if continuously used,

Volume/position detection
microcomputer board

and they would be appropriate for wearable devices. Inaddition, it is difficult to convey over words, but thematerial has a gentle texture when next to the skin, andTouch position
volume detector

this is another point that makes it ideal for continuous

PTFE nanofiber
touch sensor

use.
Figure11 shows a trial electromyography sensor. In thisWinter 2022
No.42

figure, the 3 electrodes are made to be worn separately,
but it is also possible to combine them as shown in
Figure12, and it could be considered to be used as a

Figure13 Trial touch sensor（Microcomputer board and display software from Renesas Electronics Corp.）

wristband type device.

5. Future developments
Myoelectric potential
indicator
Tension, intensity
determination

USB input

This time, we investigated the utilization of PTFE
nanofibers in flexible devices. By forming wiring on
PTFE nanofibers, we think that we have shownpossibilities as to their application that go beyond theirFor use, these 3 electrodes
are attached to the arm
USB output
PTFE
electromyography
sensorElectromyography amplifier
Noise cancellation
USB conversion

Figure11 Trial electromyography sensors（Electromyography amplifier and display software are products from Tokyo Devices Inc.）utilization as only a material. In the future, with theprogressively ageing society in Japan, we think that theuse of wearable devices in the healthcare field willincrease. In addition, there are types of devices such as
foldable smartphones that have not been seen before,
and it is predicted that various user interfaces will befurther required in the future.
To be able to follow this drastic changing society in a
flexible way like nanofibers, we will continue our efforts
on further expanding the examples we have shown here
and also produce products that benefit society.

Figure12
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Electromyography sensor, integrated type

Product Introductions

6. Conclusions
Through a collaborative effort with CONNECTECPTFE nanofiber, and CONNECTEC JAPAN’s
proprietary low temperature technology. With this, wehope that we can help realize our readers’ ideas.

JAPAN, we were able to show new possibilities forutilizing PTFE nanofibers. We think that the utilization
cases that we introduced in this report are only aportion. We consider that the development of novel
devices could be possible using Valqua’s unique material,

7. References
1）Tsuji, Setoguchi, Valqua Technology News, No. 23,
pp.13-15.

Hirotaka Mutoh

Tetsuya Komeda

Corporate Research andDevelopment Group

Corporate Research andDevelopment Group

Winter 2022
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