Basic study of surface treatment
at low discharge voltage by atmospheric microplasma
Kazuo Shimizu , Akira Umeda and Marius Blajan
Innovation and Joint Research Center, Shizuoka University, 3-5-1 Jyouhoku, Hamamatsu, 432-8561, Japan, E-mail：shimizu@cjr.shizuoka.ac.jp

1.Introduction

90

4. Results and discussion
Surface hydrophilic property was evaluated bymeasuring static contact angle with a drop ofdistilled water on the sample PEN film surface.

(a)Before treatment(b)After treatment

1050

845

640

4Conta…

35230800

9001000

Discharge power [W]Contact angle[degree]

55dFig.8 shows the effect of gas on surface treatment
of PEN film. Contact angle was not decreased when
only nitrogen was used as treating gas. Addition ofargon affected the PEN film surface and as aconsequence the contact angle decreased.

4.2 XPS analysis
X-ray photoelectron spectrometer (XPS) was used
to analyze chemical changes of the sample surface.

01100

Untreat…

Fig.5 Discharge voltage versus discharge
power and contact angle.

100 um

Fig.1 A Schematic image of microplasma
electrodes and surface treatment processof PEN film.

20(Treatment time 5sec,distance between electrodes and PEN film1 mm,
gas flow rate 5 L/min)

C-O
O-C=O

Fig.5 shows characteristics between discharge
voltage and contact angle. Decrease of contact angle
was observed with the increase of discharge voltage.
90300

295

70285

280

Fig.9 XPS C1s peaks of PEN films.

6050Untre…

4030
201000Fig.2 Image of microplasma during
discharge.

51015202530

C-O-C

O=C
O-H

Treatment time [s]Two metal circular plates covered with dielectricmaterials are faced together with a spacer (thickness100 um) in between. By applying an alternative
voltage, streamers generate to form glow-like plasma(Fig.2).

Fig.6 Relationship between treatment time andcontact angle.

3. Experimental setup

Fig.6 shows characteristics between treatment
time and contact angle. Initial contact angle of PEN(Discharge voltage 1.1 kV,
distance between electrodes and PEN film1 mm,
gas flow rate 5 L/min)film was about 80゜. The minimum contact angleof about 30゜ was obtained at treatment time of 3sec.
70d=1mm

Contact angle [degree]

656055542537532527522

Binding energy [eV]Fig.10 XPS O1s peaks of PEN films.
Fig.9 and Fig.10 show that decrease of C-H bondand increase of C-O-C bond , O=C bond and O-Hbond. Decreasing of C-H bond that is hydrophobic
functional group was one factor ofimprovinghydrophilic property of surface of PEN film..

5. Conclusions
The following conclusions were obtained by theseries of experiments.

504540(1) Surface of PEN film was modified by atmosphericmicroplasma at a discharge voltage of 1.1 kV .

3530

Fig.3 shows the experimental setup. Argon gas
supplied by a gas cylinder. A neon transformer wasused as the power source for microplasma.
Innumberable streamers were generated between theelectrodes, which generate various radicals. In seriesof experiments those active species could affect atarget surface.

290

Binding energy [eV]Intensity (arb.unit)

Contact angle [degree]80

Fig.3 An Experimental setup

C-H

Discharge voltage [V]

40 mm

Front view

30(Treatment time 10sec, discharge voltage 1.2kV, d=1 mm)

122.5 mm

Side view40

Fig.8 Effect of treating gas for the contact
angle on sample surface.

Fig.4 Images of contact angle of awaterdrop on PEN film.

PEN film

Microplasma

50

Untreated N2(5L/min) N2(2.5L/min) Ar(5L/min)+Ar(2.5L/min)

60

Carrier gas

600Spacer
Electrode70

102. Atmospheric microplasma
Atmospheric microplasma is a type of dielectricbarrier discharge which has a discharge gap in
the order of micro meters. A schematic image ofthe microplasma electrodes and surface treatment
process of PEN film is presented in Fig.1.

Contact angle [degree]80

4.１ Changes in surface hydrophilic property

Intensity(arb.unit)

PEN (polyethylene naphthalate) is a polymer withhigh thermal and chemical durability, but its surface is
not suitable for printing or gluing.
Plasma treatment has been studied to improve thePEN surface characteristics. For industry application,
plasma process in atmospheric pressure is desired
due to the low cost. Microplasma which is
atmospheric pressure non thermal plasma require
relatively low discharge voltage. Surface Treatmentof PEN film by atmospheric microplasma wasinvestigated.

5(2)The minimum contact angle of about 30゜ wasobtained at treatment time 3 sec with Ar.

Fig.7 Relationship between gas flow rateand contact angle.

(3)Surface of PEN film was chemically modified byatmospheric microplasma.

12

34Gas flow rate [L/min](Treatment time 5sec, discharge voltage 1.1 kV)
Fig.7 shows caracteristics between gas flow rateand contact angle. Decrease of contact angle wasobserved with increase of gas flow rate. When thedistance between electrodes and PEN film wasshorter, contact angle tended to be smaller.

(4)Physical deformation by heat was not confirmed
by microplasma surface treatment, since its
discharge voltage was very low.