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

1.Introduction
Polymer materials have a wide field of application forexample in food industry, medical equipments, electronic, ininformation technology industry, etc.
Plasma treatment has been studied to improve thePEN(polyethylene naphthalate) surface characteristics. For
industry application, plasma process in atmosphericpressure is desired to minimize the cost and process time.
Microplasma which is atmospheric pressure non thermal
require relatively low discharge voltage. Surface treatmentof PEN film by atmospheric microplasma was investigated.

2. Atmospheric microplasma

Atmospheric microplasma is a type of dielectric barrierdischarge which has a discharge gap in the order of micrometers. A schematic image of the miroplasma electrodes
and surface treatment process of PEN film is presented inFig.1.
SpacerElectrodePEN film

Fig.4 An example of Marx generator circuit.
Fig. 4 shows an example of Marx generator circuit. Whenthe switches(Tr2) are opened, the capacitors llinked inparallel connection are charged at a gven E.
By turning on the switches, the capacitors discharge inseries connection. The voltage will have the value E
multiplied with the number of capacitors.

4. Results and discussion
4.１ Changes in surface wettability

Carrier gas

Surface wettability was evaluated by measuring static
contact angle with a drop of distilled water on the sample
PEN film surface.

Microplasma

Fig.8 Relationship between gas flow rateand contact angle.

(Treatment time 5sec, discharge voltage -1.3 kV)
Fig.7 shows characteristics between gas flow rate andcontact angle. Decrease of contact angle was observedwith increase of gas flow rate. When the distance between
electrodes and PEN film was shorter, contact angle tended
to be smaller.

4.2 XPS analysis

X-ray photoelectron spectrometer (XPS) was used toanalyze chemical changes of the sample surface.

2.5 mm
C-Hd40 mm

100 umSide view

Front view(a)Before treatment(b)After treatment

Fig.5 Images of contact angle of a waterdrop
on PEN film.

Power consumption [W]Fig.1 A Schematic image of microplasma electrodes
and surface treatment process of PEN film.

Fig.2 Image of microplasma during discharge.
Two metal circular plates covered with dielectric materials
are faced together with a spacer (thickness 100 um) in
between. By applying an alternative voltage, streamers
generate to form glow-like plasma (Fig.2).

3. Experimental setup

Fig.9 XPS C1s peaks of PEN films.

C-O-C
O-H

O=CFig.6 Discharge voltage versus discharge powerand contact angle.

(Treatment time 5sec, distance between electrodes andPEN film1 mm, gas flow rate 5 L/min)Fig.6 shows characteristics between discharge voltage
and contact angle. Decrease of contact angle wasobserved with the increase of discharge voltage.

Fig.10 XPS O1s peaks of PEN films.
Fig.9 and Fig.10 show that decrease of C-H bond andincrease of C-O-C bond , O-H bond and O=C bond.
Decreasing of C-H bond that is hydrophobic functionalgroup was one factor of improving hydrophilic property ofsurface of PEN film.

5. Conclusions
The following conclusions were obtained by the seriesof experiments.
(1) Surface of PEN film was modified by atmosphericmicroplasma at a discharge voltage of -1.3 kV .

Fig.3 An Experimental setup
Fig.3 shows the experimental setup. Argon gas supplied bya gas cylinder. We used a Marx generator which generates
negative pulsed for generating microplasma. Innumberable
streamers were generated between the electrodes, which
generate various radicals. In series of experiments those
active species could affect a target surface.

Fig.7 Relationship between treatment timeand contact angle.

(Discharge voltage -1.3 kV,
distance between electrodes and PEN film1 mm,
gas flow rate 5 L/min)Fig.7 shows characteristics between treatment time andcontact angle. Initial contact angle of PEN film was about
73 ゜ . The minimum contact angle of about 30゜ wasobtained at treatment time of 20 sec.

(2)The minimum contact angle of about 30゜ wasobtained at treatment time 20 sec with Ar.
(3)It was confirmed to decrease hydrophobic functionalgroup on the surface of PEN film.
(4)Physical deformation by heat was not confirmed by
microplasma surface treatment, since its discharge
voltage was very low.