S4-7
The Use of Atmospheric Non-Thermal Plasma in the Industries
マルチフェーズプラズマに期待する大気環境下 低温プラズマの産業応用
Katsuyuki Takahashi
高橋克幸
Shishido electrostatic, LTD.
4-7-21, Chigasaki-higashi, Tsuzuki-ku, Yokohama 224-0033, Japan
シシド静電気株式会社 〒224-0033 横浜市都筑区茅ヶ崎東4-7-21

Corona discharge is one of the methods to produce the non-thermal plasma. The corona discharge
ionization has been mainly used for neutralization of the electrostatic charged objects in the manufacturingindustries for the prevention of electrostatic discharge problems. The long-term stability of the capabilities
is required for industrial applications to maintain the quality of the industrial products and to reduce theoperating cost. In this paper, the recent development of the corona discharge ionizer is reviewed andapplications of the ionizer in a variety of industries are described.

Voltage [kV]

52.50-2.5-5-7.5-2024

Time [ms]Fig.1. Typical waveform of AC power supply driven
by PWM inverter.
Positive charge decay time
Negative charge decay time
Discharge current

1.660

1.440

1.21200.8102103

Discharge current [µA]

2. High Efficient Electrostatic Elimination
Generally, high speed electrostatic eliminationand low offset voltage depended on the balance
between amounts of positive and negative ions are
required for performance of ionizer. The
performance declines with deterioration of highvoltage electrode caused by the dust attraction andthe abrasion by the corona discharge. The discharge
current that does not contribute to eliminate
electrostatic charge reduces the efficiency of theelectrostatic elimination and causes the electrodedeterioration. The efficiency is affected by thewaveform of the applied voltage. The optimizationof applied voltage is important to achieve long-term
stability in the performance. An intermittent pulse
voltage AC power supply has been developed forhigh efficient electrostatic elimination [2].
Fig.1 shows typical waveform of the output
voltage of the intermittent pulse voltage AC power
supply. The voltage is generated by high voltage
pulse transformer driven by a PWM inverter [2].
The timing, repetition rate and the amplitude of the7.5

Charge decay time [s]1. Introduction
Corona discharge is one of the methods toproduce the non-thermal plasma under atmosphericpressure. The high concentration of air ion isgenerated by the corona discharge with low-powerand high-voltage power supply. The corona
discharge ionizer has been widely used to eliminate
electrostatic charge on insulators in variety ofmanufacturing industries for the prevention ofelectrostatic discharge (ESD) problems [1].
In this paper, the recent development andindustrial uses of the corona discharge ionizer arereviewed.

0Pulse repetition rate [Hz]Fig.2. Static charge decay time and ozoneconcentration as a function of pulse repetition rate forvarious air velocities.

each pulse are adjustable arbitrarily and optimized
for the electrostatic elimination.
Fig. 2 shows the static charge decay time anddischarge current as a function of pulse repetition
rate. The charge decay time was measured using acharged plate monitor (Trek, Model158) having a

Offset voltage [V] Charge decay time [s]250 Hz, Fan type

1.5
10.5

Charge polarity
Positive
Negative100-10-20-3005000
10000
15000
Time [h]Fig.3. Time history of the charge decay time and theoffset voltage of the electrostatic eliminator using
the intermittent AC pulse.

capacitor of 20 pF. The pulse width is fixed at 290
us. The minimum value of charge decay time isobtained at the pulse repetition rate of 250 Hz.
When the pulse repetition rate is less than 250 Hz,
the concentration of the air ion decreases owing to
the decrease of number of discharges. Above 250
Hz, the amount of ion reached to the charged plate
monitor decreases by increase of the ion loss rate ofion-ion recombination [3]. The discharge current
increases with increasing the pulse repetition rate.
The result indicates that the efficiency for theelectrostatic elimination decrease above theoptimum pulse repetition rate.
Fig. 3 shows the time history of the charge decay
time and the offset voltage of the electrostaticeliminator using the intermittent AC pulse. The
decay time and the offset voltage are maintained forover 15,000 hour continuous operation, which isstabilized several times longer than that ofconventional applied voltage type such as DC andcommercial frequency AC.
3. Use of Ionizer
The ionizer has been mainly used in electronic
device manufacturing processes within the offset
voltage of several ten volts to prevent ESD event
causes damage to the devices. Especially, a
perfectly balanced ionizer with the offset voltage
below 1~10 V has been required in the HDD
manufacturing processes.
On the dust removal system, the electrostatic
charged dust particles are neutralized by the ionizer
to collect and transport under vacuum easily byreducing the electrostatic attracting force. The

electrostatic elimination of the charged objects also
contributes to reduce the risk of the dust attraction
to the objects. The system has been used various
processes such as film manufacturing, molding
process and food process.
Corona discharge produced by the ionizer
induces various chemical reactions, which ispossible to treat the harmful gas with low-power
and long-term stability [4]. The ethylene gas
treatment system using the ionizers is investigated
for the freshness preservation and rottenness
prevention of fruit and vegetable in containertransport [5]. The concentration of ethylene
released from the fruits in a 20-feet container
increased 7.5 ppm per a day and reached about
150 ppm after 20 days storage. The concentration iskept 7 ppm during 20 days and the fruit quality is
maintained using the treatment system. This work
was supported by Scientific technique researchpromotion program for agriculture, forestry,
fisheries and food industry in 2011-2014 (No.
23059).
4. Conclusions
The recent development of the corona discharge
ionizer for electrostatic removal and the industrial
applications are described. The environmental air
frequently contains the pollutions such as dust
particle, moisture and harmful gas. The surface
contamination of the ionizer by attracting thepollutions causes the decrease of the resistance
between high voltage and ground terminals, whichleads the performance degradation and the safetydeterioration. The long term stability of theperformance is required to maintain the quality ofthe products. Furthermore, short cleaning intervalof the unit increases the operating cost. The stability
and safety are affected by the structure of theelectrodes and applied voltage waveform. It isrecommended that the corona discharge system
must be evaluated on the balance between theperformance and the long-term stability.
References[1] H. Inaba, S. Sakata, T. Yoshida, T. Okada and T.
Ohimi: IEEE Trans. Semicond. Manufact. 5 (1992)
234.
[2] K. Takahashi, I Hiyoshi, Y. Enomoto and H. Nagata:
J. Inst. Electrostat. Jpn. 38 (2014) 124.
[3] A. Ohsawa: J. Electrostat. 63 (2003) 767.
[4] H. Kim: Plasma Process. Polym. 1 (2004) 91.
[5] K. Takahashi, T. Uchino, S. Koide and K. Takaki: J.
Plasma Fusion Res. 90 (2014) [in press]