U.S. patent application number 11/826948 was filed with the patent office on 2008-07-03 for plasma processing apparatus.
This patent application is currently assigned to NGK INSULATORS, LTD.. Invention is credited to Yuichiro Imanishi, Naohiro Shimizu.
Application Number | 20080159925 11/826948 |
Document ID | / |
Family ID | 39584251 |
Filed Date | 2008-07-03 |
United States Patent
Application |
20080159925 |
Kind Code |
A1 |
Shimizu; Naohiro ; et
al. |
July 3, 2008 |
Plasma processing apparatus
Abstract
This invention concerns with the plasma inactivating method and
processor that can inactivate the surface of the object without
causing the degradation inside of it. The inactivation of toxins on
the surface of the object proceeds as removing the toxins by
nitriding or oxidizing the toxins by the following triple effects,
the sharp pulsed electric field by the supply of the electric
pulses, the generated N-radicals (N*) contained inside of the
plasma in the surrounding gases composed mainly by N.sub.2 gas
under the low pressure.
Inventors: |
Shimizu; Naohiro;
(Miura-City, JP) ; Imanishi; Yuichiro;
(Nagoya-City, JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 320850
ALEXANDRIA
VA
22320-4850
US
|
Assignee: |
NGK INSULATORS, LTD.
NAGOYA
JP
|
Family ID: |
39584251 |
Appl. No.: |
11/826948 |
Filed: |
July 19, 2007 |
Current U.S.
Class: |
422/186.05 |
Current CPC
Class: |
H05H 1/2406 20130101;
H05H 2001/2412 20130101; A61L 2/10 20130101; H05H 2245/1225
20130101; A61L 2/14 20130101 |
Class at
Publication: |
422/186.05 |
International
Class: |
B01J 19/12 20060101
B01J019/12 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 27, 2006 |
JP |
2006-351345 |
Claims
1. A plasma processing apparatus for inactivating toxins sticking
to the surface of a treatment object, comprising: ambient gas
adjusting means for adjusting ambient gas of a space, in which an
inactivation process is scheduled, so as to provide a nitrogen
ambient gas; an electrode pair disposed in the space; a pulse power
supply for applying electric pulses repeatedly to the electrode
pair, inducing fine streamer discharge without inducing arc
discharge; and a reflection member for reflecting back the short
wavelength ultraviolet ray into the inside of the space, the short
wavelength ultraviolet ray going from the inside of the space to
outside, wherein toxins are nitrided and oxidized, and toxins are
removed from the surface of tho treatment object, by treating
toxins by applying pulse electric field generated by application of
the electric pulse to the electrode pair, nitrogen radicals
contained in the plasma generated in the nitrogen ambient gas due
to fine streamer discharge, and short wavelength ultraviolet rays
generated by the nitrogen ambient gas due to fine streamer
discharge.
2. The plasma processing apparatus according to claim 1, wherein
the toxins are endotoxin or abnormal prion.
3. The plasma processing apparatus according to claim 1, wherein
the half width of pulse width of electric pulse is 50 to 300
ns.
4. The plasma processing apparatus according to claim 1, wherein
the ambient gas adjusting means supplies nitrogen gas from an anode
side, and exhausts nitrogen gas from a cathode side, the anode and
the cathode side implementing the electrode pair.
5. The plasma processing apparatus according to claim 1, wherein
the ambient gas adjusting means includes evacuating means for
evacuating the space.
6. The plasma processing apparatus according to claim 1, further
comprising: temperature adjusting means for adjusting the
temperature of the nitrogen ambient gas.
7. The plasma processing apparatus according to claim 1, wherein
the reflection member reflects short wavelength ultraviolet rays by
an aluminum film.
Description
[0001] This application is based on application No. JP2006-351345
filed in Japan, the contents of which are hereby incorporated by
reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a plasma processing
apparatus for inactivating toxins such as endotoxins and abnormal
prions.
[0004] 2. Description of the Background Art
[0005] Endotoxins are lipopolysaccharides which form the outer
membrane of the cell wall of gram-negative bacteria. It is known
that only a microscopic amount of endotoxins have heat buildup, and
it is necessary to inactivate endotoxins sticking to medical tools
in order to prevent medical accidents. As for methods for
inactivating endotoxins, a gamma ray method, an electron beam
method, an ethylene oxide gas method, a hydrogen peroxide gas
plasma method, an autoclave method and a dry heat method have been
examined (see, for example, Kazunari Hosofuchi et al.,
"Inactivation of Dry Endotoxins in Accordance with Various
Sterilizing Methods," Tokyo Metropolitan Industrial Technology
Laboratory Research Report, Tokyo Metropolitan Industrial
Technology Laboratory, 1999, No. 2, pp. 126 to 129).
[0006] In accordance with the conventional methods other than the
dry heat method, however, the activity of endotoxins cannot be
sufficiently lowered. In the case where typical processing
conditions are adopted, for example, the activity of endotoxins can
only be lowered to approximately 1/4 in accordance with the gamma
ray method, the electron beam method or the ethylene oxide gas
method, to approximately 1/20 in accordance with the hydrogen
peroxide gas plasma method, and to approximately 1/9 in accordance
with the autoclave method. Meanwhile, though the activity of end
toxins can be lowered to approximately 1/10.sup.5 in accordance
with the dry heat method, it is necessary to heat a treatment
object to approximately 250.degree. C., and therefore, there is a
problem, such that the treatment object is damaged.
[0007] Here, this problem with inactivation is also present with
toxins other than endotoxins such as abnormal prions, which are
assumed to be toxins causing bovine spongiform encephalopathy.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a diagram showing dissociation energy of various
gas molecules;
[0009] FIG. 2 is a schematic diagram illustrating discharge states
and rough voltage waveforms of electric pulses;
[0010] FIG. 3 is a schematic diagram illustrating a general
structure of endotoxin;
[0011] FIG. 4 is a perspective view of a reactor of a plasma
processing apparatus in an embodiment;
[0012] FIG. 5 is a cross-sectional view of the reactor of the
plasma processing apparatus in an embodiment;
[0013] FIG. 6 is a diagram illustrating wavelength dependence of
reflectivity of various metal films;
[0014] FIG. 7 is a diagram showing an example of voltage waveform
and current waveform of electric pulse;
[0015] FIG. 8 is a diagram showing a structure of an IES
circuit;
[0016] FIG. 9 is a diagram showing an operation of the IES
circuit;
[0017] FIG. 10 is an explanatory diagram illustrating operations of
the plasma processing apparatus; and
[0018] FIG. 11 is a diagram showing drops of activity of
endotoxins.
SUMMARY OF THE INVENTION
[0019] The present invention relates to a plasma processing
apparatus for inactivating toxins such as endotoxins and abnormal
prions.
[0020] According to the present invention, a plasma processing
apparatus for inactivating toxins sticking to the surface of a
treatment object, includes: ambient gas adjusting means for
adjusting ambient gas of a space, in which an inactivation process
is scheduled, so as to provide a nitrogen ambient gas; an electrode
pair disposed in the space; a pulse power supply for applying
electric pulses repeatedly to the electrode pair, inducing fine
streamer discharge without inducing are discharge; and a reflection
member for reflecting back the short wavelength ultraviolet ray
into the inside of the space, the short wavelength ultraviolet ray
going from the inside of the space to outside, wherein toxins are
nitrided and oxidized, and toxins are removed from the surface of
the treatment object, by treating toxins by applying pulse electric
field generated by application of the electric pulse to the
electrode pair, nitrogen radicals contained in the plasma generated
in the nitrogen ambient gas due to fine streamer discharge, and
short wavelength ultraviolet rays generated by the nitrogen ambient
gas due to fine streamer discharge.
[0021] As a result, toxins sticking to the treatment object can be
inactivated without damaging the treatment object.
[0022] Accordingly, an object of the present invention is to
inactivate toxins sticking to the treatment object without damaging
the treatment object.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0023] <1 Inactivation of Toxins>
[0024] In the plasma processing apparatus according to the present
invention, a pulse electric field, nitrogen radicals (N*) and
ultraviolet rays including short wavelength ultraviolet rays of
which the wavelength is no shorter than 100 nm and no longer than
280 nm (also referred to as "far ultraviolet rays" or "UV-C") work
on toxins in a complex manner, so that the toxins are nitrided and
oxidized, and removed from the surface of the treatment object.
[0025] Here, "toxins" are biologically active substances which are
harmful to living things, typically endotoxins and abnormal prions.
Here, a pulse electric field, nitrogen radicals and short
wavelength ultraviolet rays may work both on the toxins and the
surface of the treatment object, depending on the treatment object
to which the toxins stick, and in some cases, this synergetic
effect makes inactivation of toxins progress.
[0026] In the plasma processing apparatus according to the present
invention, the treatment object to which toxins stick is placed
between a pair of electrodes and an electric pulse having a sharp
rise is applied to this electrode pair so that the pulse electric
field having a sharp rise works on the toxins. This is an
application of the knowledge that when toxins are exposed to an
electric field, such a phenomenon can be observed that a polarized
charge is induced on the anode side and the cathode side of the
toxins so that an internal electric field which is stronger than
the external electric field is generated inside the toxins, and
therefore, when the toxins are exposed to a pulse electric field
having a sharp rise, the potential gap between the anode side and
the cathode side of the toxins can be abruptly increased, and thus,
electrical impact can be applied to the toxins.
[0027] In addition, in the plasma processing apparatus according to
the present invention, the treatment object to which toxins stick
is put between a pair of electrodes which are installed in a
nitrogen atmosphere, and an electric pulse having a sharp rise is
applied to the pair of electrodes so as to cause fine streamer
discharge, and thus, nitrogen radicals included in the plasma
generated in the nitrogen atmosphere work on the toxins. Here, the
reason why nitrogen radicals are selected as active species, that
is, the reason why plasma is generated in a nitrogen atmosphere, is
that activation of nitrogen radicals is significantly higher than
for other active species, for example oxygen radicals. This is
clear from the fact that the dissociation energy of nitrogen
molecules (N.sub.2) is 9.91 eV and the dissociation energy of
oxygen molecules (O.sub.2) is 5.21 eV, as shown in FIG. 1, where
the dissociation energy of various gas molecules is listed in a
table. In addition, the fact that the life of nitrogen radicals is
long, the life of biradicals of triplet nitrogen (.sup.3.SIGMA.u),
for example, reaches 10 ms, is one reason why nitrogen radicals are
selected as the active species. In addition, the fact that nitrogen
gas is easily available at low cost and easy to handle is also one
reason why nitrogen radicals are selected as the active
species.
[0028] Furthermore, in the plasma processing according to the
present invention, the treatment object to which toxins stick is
irradiated with ultraviolet rays including short wavelength
ultraviolet rays of which the wavelength is 250 nm which are
generated in a nitrogen atmosphere due to fine streamer discharge,
and thus, the short wavelength ultraviolet rays work on the toxins.
Here, short wavelength ultraviolet rays are used because toxins are
sensitive to short wavelength ultraviolet rays.
[0029] <2 Fine Streamer Discharge>
[0030] FIG. 2 is a diagram schematically showing the state of
discharge caused by applying an electric pulse to a pair of
electrodes 81 and 82 and schematic waveforms of the voltage of the
electric pulse (at the time of no load). In FIG. 2, the schematic
waveforms of the voltage of the electric pulse are shown as a graph
plotting the change in the voltage V (longitudinal axis) relative
to the time t (lateral axis).
[0031] As shown in FIG. 2, when the pulse width .DELTA.t of the
electric pulse reaches approximately 100 ns, secondary electrons
which are released when positive ions collide with the cathode 82
ionize nitrogen molecules, and thus, glow discharge for generating
new positive ions is caused.
[0032] Meanwhile, in the case where the ratio of increase in the
voltage V along time dV/dt is approximately 30 to 50 kV/.mu.s when
the electric pulse rises, a streamer 83 starts growing from the
anode 81 to the cathode 82 when the pulse width .DELTA.t reaches
approximately 100 ns. In addition, in the case where the pulse
width .DELTA.t is approximately 100 to 400 ns, the streamer 83
stops growing at the initial stage, where short streamers 83 are
interspersed between the anode 81 and the cathode 82. Meanwhile, in
the case where the pulse width .DELTA.t is approximately 500 ns to
1000 ns, the streamer 83 grows all-out and becomes of such a state
that a long and branched streamer 83 exists between the anode 81
and the cathode 82. In the plasma processing apparatus according to
the present invention, fine streamer discharge gained by stopping
discharge at the initial stage of growth of the streamer 83 is
used, in order to prevent the streamer 83 from fully growing and
electrically connecting the anode 81 and the cathode 82. This is
because toxins can be uniformly inactivated when highly uniform
fine streamer discharge is used.
[0033] Furthermore, when the pulse width .DELTA.t reaches
approximately 1000 ns, a localized concentration of current is
created, and finally, arc discharge is caused.
[0034] In the above description, "approximately" is used for the
pulse width .DELTA.t and the range of the ratio of rise in the
voltage V along time dV/dt at the time of the rise because these
change depending on the concrete configuration of the plasma
processing apparatus including distance between the pair of
electrodes 81 and 82 and the structures of the anode 81 and the
cathode 82 as well as the pressure of the nitrogen atmosphere.
Accordingly, whether or not fine streamer discharge is gained
should be determined not only from the pulse width .DELTA.t and the
ratio of the rise in the voltage V along time dV/dt at the time of
the rise, but also by observing the actual discharge.
[0035] In addition, the conditions in the schematic waveform of the
voltage in the electric pulse are "at the time of no load" because
the schematic waveform of the voltage of the electric pulse which
is actually applied across the pair of electrodes 81 and 82 varies
together with variation in the concrete configuration of the plasma
processing apparatus, including the distance between the pair of
electrodes 81 and 82 and the structures of the anode 81 and the
cathode 82, oven when the power supply for the pulse is operated
under the same conditions.
[0036] <3 General Structure of Endotoxins>
[0037] FIG. 3 is a diagram schematically showing the general
structure of an endotoxin which forms the outer membrane of the
cell wall of a gram-negative bacterium, which is an example of a
toxin. As shown in FIG. 3, the endotoxin is formed of a
polysaccharide portion and a lipid portion; the polysaccharide
portion is formed of an O-specific chain and cores (internal core
and external core), and the lipid portion is formed of a lipid A
which becomes an active portion. In the plasma processing apparatus
according to the present invention, a pulse electric field,
nitrogen radicals and short wavelength ultraviolet rays work on the
endotoxin so that the endotoxin is nitrided and oxidized, and the
endotoxin is removed from the surface of the treatment object as a
gas, and thus, the endotoxin is inactivated.
[0038] Here, abnormal prions and other toxins can also be
inactivated on the basis of the same principle.
[0039] <4 Example of Configuration of Plasma Processing
Apparatus>
[0040] <4.1 Reactor>
[0041] FIGS. 4 and 5 are schematic diagrams showing a reactor 11 of
a plasma processing apparatus 1 according to a desirable embodiment
of the present invention; FIG. 4 is a perspective diagram showing
the external structure of the reactor 11, and FIG. 5 is a cross
sectional diagram showing the internal structure of the reactor 11.
FIG. 5 also shows attachments for the reactor 11 which forms the
plasma processing apparatus 1.
[0042] As shown in FIG. 4, the reactor 11 is a batch type reaction
container where a nitrogen gas is supplied through an air supplying
opening on the upper side, and the nitrogen gas can be discharged
from an air discharging opening on the lower side.
[0043] An electric pulse is applied across a pair of electrodes 112
and 113 inside the reactor 11 so that plasma is generated in a
plasma discharge gap 119 between the pair of electrodes 112 and 113
and a treatment object 71 is exposed to the generated plasma, and
thus, toxins sticking to the treatment object 71 are
inactivated.
[0044] As shown in FIG. 5, silica mirrors 111 and 112 where through
holes 1115 and 1125 are created are installed horizontally at a
distance in the up-down direction inside the reactor 11, and an
electrode rod 113 which extends in the front-rear direction is
installed horizontally between these. The power supply for a pulse
13 is connected to the pair of electrodes 112 and 113 which are
formed of the silica mirror 112 which becomes the cathode and the
electrode rot 113 which becomes the anode. A nitrogen gas is
supplied into the reactor 11 from a nitrogen gas tank 14 through
the through hole 1115, and the nitrogen gas is discharged from
inside the reactor 11 through the through hole 1125 and an air
discharging opening 1166 using a discharging pump 15. The pressure
inside the reactor 11 can be measured using a pressure gauge 16. In
addition, a halogen lamp heater 114 and an optical fiber
thermometer 115 are installed inside the reactor 11. The halogen
lamp heater 114 and the optical fiber thermometer 115 are connected
to a controller 17.
[0045] <4.2 Silica Mirrors>
[0046] The silica mirrors 111 and 112 are made of silica glass
plates 1111 and 1121 where aluminum films 1112 and 1122 are
respectively vapor deposited on one of the main surfaces. The other
main surface of the silica glass plates 1111 and 1121, on which the
aluminum film 1112 and 1122 is not vapor deposited, faces the
plasma discharge gap 119. The silica mirror 111 reflects short
wavelength ultraviolet rays 1191 which go upward from inside the
reactor 11 back into the reactor 11. The silica minor 112 reflects
short wavelength ultraviolet rays 1191 which go downward from
inside the reactor 11 back into the reactor 11. In this manner,
when a reflective member for returning short wavelength ultraviolet
rays 1191 which go outward from inside the reactor 11 back into the
reactor 11 is provided, the efficiency of using short wavelength
ultraviolet rays 1191 emitted from the nitrogen atmosphere can be
increased, so that the amount of short wavelength ultraviolet rays
1191 with which the treatment object 71 is irradiated can be
increased, and therefore, the efficiency of inactivation of toxins
can be increased. The mirror surface from which short wavelength
ultraviolet rays 1191 are reflected is formed of an aluminum film
because the reflectance of aluminum films for short wavelength
ultraviolet rays is extremely high (approximately 90%), as shown in
FIG. 6, which is a graph showing the dependency of the reflectance
of various types of metal films on the wavelength, which can
contribute to efficient inactivation of toxins.
[0047] <4.3 Electrodes>
[0048] The material for the electrode rod 113 is INCONEL
(registered trademark), which has excellent resistance against
plasma. Here, this does not preclude use of materials other than
INCONEL (registered trademark), such as materials of which the main
component is, for example, tungsten, molybdenum, manganese,
titanium, chromium, zirconium, nickel, silver, iron, copper,
platinum, palladium or another metal, for the electrode rod 113.
Here, "metal" includes alloys which contain two or more types of
metal, for example iron alloys, typically nickel alloys or
stainless steel. Here, FIG. 5 shows only one electrode rod 113, but
two or more electrode rods 113 may be arranged in the left-right
direction with a distance in-between. In addition, it is also
possible to form the anode of an electrode plate, but in this case,
it is desirable to adopt an electrode plate in comb form or net
form so that the opposite side can be seen through the electrode
plate, and thus prevent the anode from blocking short wavelength
ultraviolet rays 1191 and the treatment object 71 from not being
irradiated with short wavelength ultraviolet rays 1191.
[0049] Here, though the silica mirror 112 functions as the cathode,
and also as a reflective member for reflecting short wavelength
ultraviolet rays 1191 in the reactor 11, this does not preclude
installation of a cathode and a reflective member as independent
members.
[0050] <4.4 Power Supply for Pulse>
[0051] The power supply for a pulse 13 repeatedly applies an
electric pulse which causes fine streamer discharge across the pair
of electrodes 112 and 113 without causing arc discharge.
Concretely, the power supply for a pulse 13 repeatedly applies an
electric pulse of which the pulse width measured as full-width at
half-maximum is 50 to 300 ns across the pair of electrodes 112 and
113. FIG. 7 shows an example of the waveform of the voltage and the
waveform of the current of the electric pulse applied across the
pair of electrodes 112 and 113 by the power supply for a pulse 13.
FIG. 7 shows the change in a voltage V2 and a current I2 of the
electric pulse (longitudinal axis) along time (lateral axis), and
the pulse width measured as full-width at half-maximum is
approximately 100 nm.
[0052] It is desirable to adopt an inductive energy storing type
power supply circuit (hereinafter, referred to as "IES circuit")
using a static induction type thyristor (hereinafter, referred to
as "SIThy") as the power supply for a pulse 13. Here, the IES
circuit is described in detail in Katsuji Iida, Takeshi Sakuma,
"Inductive Energy Storage Type Power Supply for Pulse," 15.sup.th
SI Device Symposium (2002).
[0053] First, in reference to FIG. 8, the configuration of the IES
circuit (power supply for a pulse) 13 is described. The IES circuit
13 includes a low voltage direct current power supply 131. A
voltage E of the low voltage direct current power supply 131 may be
much lower than the peak value of the voltage of the electric pulse
generated by the IES circuit 13. Even in the case where a peak
value V.sub.LP of a voltage V.sub.L generated at both ends of the
below described inductor 133 roaches sovoral kV, for example, the
voltage E of the low voltage direct current power supply 131 may be
several tens of V. The lower limit of the voltage E is determined
to be no lower than the latching voltage of a below described SIThy
134. The IES circuit 13 can use the low voltage direct current
power supply 131 as an electric energy source, and therefore, can
be made compact and low-cost.
[0054] The IES circuit 13 is provided with a capacitor 132 which is
connected in parallel with the low voltage direct current power
supply 131. The capacitor 132 lowers the apparent impedance of the
low voltage direct current power supply 131, and thus strengthens
the discharge ability of the low voltage direct current power
supply 131.
[0055] Furthermore, the IES circuit 13 is provided with the
inductor 133, the SIThy 134, a MOSFET (Metal Oxide Semiconductor
Field Effect Transistor) (hereinafter, referred to as "FET") 135, a
gate drive circuit 136 and a diode 137. In the IES circuit 13, the
positive electrode of the low voltage direct current power supply
131 and one end of the inductor 133 are connected, the other end of
the inductor 133 and the anode of the SIThy 134 are connected, the
cathode of the SIThy 134 and the drain of the FET 136 are
connected, and the source of the FET 136 and the negative electrode
of the low voltage direct current power supply 131 are connected.
In addition, in the IES circuit 13, the gate of the SIThy 134 and
the anode of the diode 137 are connected, and the cathode of the
diode 137 and one end of the inductor 133 (positive electrode of
the low voltage direct current power supply 131) are connected. The
gate drive circuit 136 is connected to the gate and the source of
the FET 135.
[0056] The SIThy 134 can be turned on and off in response to the
gate signal.
[0057] The FET 135 is a switching element of which the state of
conduction between the drain and the source changes in response to
a gate signal V.sub.C supplied from the gate drive circuit 136. It
is desirable for the on voltage or on resistance of the FET 135 to
be low. In addition, it is required for the withstand voltage of
the FET 135 to be higher than the voltage E of the low voltage
direct current power supply 131.
[0058] The diode 137 is provided in order to block the current
which flows in the case where a positive bias is applied to the
gate of the SIThy 134, that is, to prevent the SIThy 134 from being
driven by a current in the case where a positive bias is applied to
the gate of the SIThy 134.
[0059] The inductor 133 functions as an inductive element having
self-inductance, and a load 139 (here, the pair of electrodes 112
and 113) are connected in parallel to the two ends. Here, the
primary side of a boosting transformer is used as the inductor 133,
and the load 139 can be connected to the two ends on the secondary
side of the boosting transformer so that an electric pulse of which
the peak value of the voltage is higher can be gained.
[0060] Next, the operation of the IES circuit 13 is described in
reference to FIG. 9. FIG. 9 shows the gate signal V.sub.C supplied
to the FET 135, the state of conductance of the SIThy 134, a
current I.sub.L which flows through the inductor 133, the voltage
V.sub.L across the two ends of the inductor 133 and the change in a
voltage V.sub.AG between the anode and the gate of the SIThy 134
(longitudinal axis) along time (lateral axis) in this order from
the top.
[0061] First, when the gate signal V.sub.C is switched from off to
on at time t.sub.0, a state of conduction is gained between the
drain and the source of the FET 135. As a result, the gate of the
SIThy 134 is biased positive relative to the anode, and therefore,
a state of conduction is gained between the anode and the cathode
of the SIThy 134 ("A-K conduction" in the figure), and the current
I.sub.L, starts increasing.
[0062] When the gate signal V.sub.C is switched from on to off at
time t.sub.1, which is around the time when the current I.sub.L
reaches a peak value I.sub.LP, a state of non-conduction is gained
between the drain and the source of the FET 135, and a state of
conduction is gained between the anode and the gate of the SIThy
134 ("A-G conduction" in the figure). As a result, the current
I.sub.L decreases in sync with the expansion of the depletion layer
in the SIThy 134 between time t.sub.2 and time t.sub.3 ("expansion
of depletion layer" in the figure), and at the same time, the
voltage V.sub.L and the voltage V.sub.AG abruptly rise.
[0063] In addition, after the voltage V.sub.L and the voltage
V.sub.AG reach the peak value V.sub.LP and the peak value
V.sub.AGP, respectively, at time t.sub.3, and the direction of the
current I.sub.L is reversed, the current I.sub.L increases in sync
with contraction of the depletion layer in the SIThy 134 between
time t.sub.3 and time t.sub.4 ("contraction of depletion layer" in
the figure), and at the same time, the voltage V.sub.L and the
voltage V.sub.AG abruptly lower.
[0064] In addition, when the SIThy 134 becomes of a state of
non-conduction at time t.sub.4 ("non-conduction" in the figure),
the current I.sub.L decreases as the time approaches time t.sub.5,
and at the same time, the voltage V.sub.L and the voltage V.sub.AG
become 0.
[0065] <4.5 Adjustment of Temperature>
[0066] The controller 17 monitors the temperature of the nitrogen
atmosphere using the optical fiber thermometer 115 and controls the
power supplied to the halogen lamp heater 114, and thus, adjusts
the temperature of the nitrogen atmosphere. As a result, the
temperature of the nitrogen atmosphere can be made appropriate for
inactivation, and therefore, toxins sticking to the treatment
object 71 can be efficiently inactivated. A ceramic heater or the
like can, of course, be used instead of the halogen lamp heater
114. Here, when the silica mirror 112, where a silica glass plate
1121 which functions as a dielectric barrier is coated with an
aluminum film 1122, is used as a cathode, the time it takes for the
current to stop after an electric pulse is applied across the pair
of electrodes 112 and 113 becomes longer than in the case where a
metal plate which is not coated with a silica glass plate 1121 is
used as the cathode. Accordingly, when the silica mirror 112, where
an aluminum film 1122 is coated with a silica glass plate 1121 is
used as the cathode, the inputted power when an electric pulse is
applied across the pair of electrodes 112 and 113 becomes greater
than in the case where a metal plate which is not coated with a
silica glass plate 1121 is used as the cathode, and therefore, the
temperature in the nitrogen atmosphere can be increased by applying
an electric pulse across the pair of electrodes 112 and 113.
[0067] <4.6 Adjustment of Atmosphere>
[0068] In the reactor 11, a nitrogen gas is supplied from the
electrode rod 113 side, which becomes the anode, and the nitrogen
gas is discharged from the silica mirror 112 side, which becomes
the cathode, and thus, the atmosphere inside the reactor 11 is
adjusted to a nitrogen atmosphere. Nitrogen gas is supplied and
discharged in this manner because a nitrogen gas flow directed to
the cathode from the anode can be created parallel to the pulse
electric field, and therefore, plasma can be uniformly generated,
so that toxins sticking to the treatment object 71 can be
inactivated uniformly. In addition, there are advantages with
creating such a nitrogen gas flow, such that it becomes difficult
for oxygen gas to be mixed in, preventing ozone from being
generated to such an extent that no practical problems are caused,
and the distance between the pair of electrodes 112 and 113 can be
increased, so that toxins sticking to three-dimensional treatment
object 71 can be inactivated. Here, in the case where nitrogen gas
is supplied through a number of through holes 1115, it is desirable
for nitrogen gas which passes through a pressure loss member
mounted on the top surface of the silica mirror 111, for example
layered metal nets or a porous body of ceramics, such as alumina or
SiC, to be blow out through the through holes 1115. This is in
order to prevent the nitrogen gas from being blown out only through
the through holes 1115 in the vicinity of the air supplying opening
and inactivation of toxins from becoming non-uniform.
[0069] Furthermore, the pressure inside the reactor 11 is reduced
to 10,000 to 50,000 Pa ( 1/10 to 1/2 of atmospheric pressure), more
desirably to 20,000 to 40,000 Pa, using an air discharging pump 15
so that the distance between the pair of electrodes 112 and 113 can
be increased (typically five times or more than in the case of
atmospheric pressure) and toxins sticking to three-dimensional
objects of treatment 71 can be inactivated. Such fine streamer
discharge caused under reduced pressure contributes to prolonging
the life of nitrogen radicals 1192 (typically ten times or more
than in the case of atmospheric pressure) and efficient
inactivation of toxins sticking to the treatment object 71. Here,
in order to maintain an appropriate pressure in the nitrogen
atmosphere, prevent chemical species created through reaction of
the nitrogen radicals 1192 from remaining, and appropriately
discharge the chemical species through the plasma discharge gap
119, it is desirable for the total hole area S.sub.2 of the through
holes 1125 to be greater than a total hole area S.sub.1 of the
through holes 1115, as well as for a total hole area S.sub.3 of the
air discharging openings 1166 to be greater than a total hole area
S.sub.2 of the through holes 1125.
[0070] <5 Operation of Plasma Processing Apparatus>
[0071] FIG. 10 is a diagram for illustrating the operation of the
plasma processing apparatus 1. FIG. 10 is a diagram showing whether
or not heating using the halogen lamp heater 114 is carried out,
whether or not discharge using the air discharging pump 15 is
carried out, whether or not application of an electric pulse across
the pair of electrodes 112 and 113 is carried out, and whether or
not a nitrogen gas is supplied for each of the step of preheating
S101, the step of plasma processing S102 and the step of cooling
S103.
[0072] When the door is opened and the treatment object 71 is
placed on the silica mirror 112 and the door closed again, the
plasma processing apparatus 1 starts the step of preheating S101.
In the step of preheating S101, heating using a halogen lamp heater
114 and discharging of gas using an air discharging pump 15 are
carried out, so that the inside of the reactor 11 is heated.
[0073] In the subsequent step of plasma processing S102, heating
using the halogen lamp heater 114 is stopped and discharging of gas
using the air discharging pump 15 continues, while application of
an electric pulse across the pair of electrodes 112 and 113 and
supply of a nitrogen gas are started. Heating using the halogen
lamp heater 114 is stopped in the step of plasma processing S102
because the temperature in the nitrogen atmosphere can be
maintained even when heating is stopped, because of the input of
power through application of the electric pulse. In addition,
discharging of gas using the air discharging pump 15 continues so
that a state where the pressure inside the reactor 11 is reduced
can be maintained and a nitrogen gas flow can be created parallel
to the pulse electric field. In the step of inactivation, a
relatively small amount of nitrogen gas is supplied into the
reactor 11, and the atmosphere inside the reactor 11 is adjusted to
a nitrogen atmosphere. In addition, plasma processing is carried
out on the treatment object 71 using the plasma generated in the
plasma discharge gap 119 so that the pulse electric field generated
through application of an electric pulse across the pair of
electrodes 112 and 113, nitrogen radicals 1192 included in the
plasma generated in the plasma discharge gap in the nitrogen
atmosphere due to the fine streamer discharge, and short wavelength
ultraviolet rays 1191 emitted from the nitrogen atmosphere due to
the fine streamer discharge work on toxins sticking to the
treatment object 71, and thus, the toxins are nitrided and
oxidized, and removed from the surface of the treatment object 71.
As a result, in the plasma processing apparatus 1, toxins sticking
to the treatment object 71 can be inactivated without damaging the
treatment object 71.
[0074] In the subsequent step of cooling S103, application of an
electric pulse across the pair of electrodes 112 and 113 and
discharging of gas using the air discharging pump 15 are stopped,
while supply of a nitrogen gas continues. In the step of cooling
S103, a relatively large amount of nitrogen gas is supplied into
the reactor 11 and the inside of the reactor 11 is cooled. In this
step of cooling S103, it becomes possible to safely remove the
treatment object 71 from inside the reactor 11.
EXAMPLE
[0075] In the present example, in the plasma processing apparatus
1, an electric pulse where the peak value of the voltage was 19.0
kV and the frequency was 2.5 kHz was applied across the pair of
electrodes 112 and 113, and the reduction in the activity of
endotoxins as a result of plasma processing under reduced pressure
was evaluated while the temperature of the nitrogen atmosphere and
the processing time for plasma processing were changed.
"Lipopolysaccharides from Escherichia Coli 0111" made by Sigma
Aldrich Japan K.K. was selected as an endotoxin, and "Limulus ES-II
Test Wako" made by Wako Pure Chemical Industries, Ltd. was selected
as a limulus reagent, and the activity of the endotoxin was
measured using "Toxinometer ET-2000/J" made by Wako Pure Chemical
Industries, Ltd. FIG. 11 shows the results. FIG. 11 shows the
change in the concentration (longitudinal axis) of the endotoxin in
the specimen along the processing time (lateral axis) for plasma
processing for respective temperature ranges in the nitrogen
atmosphere (28 to 45.degree. C., 60 to 65.degree. C., and 73 to
83.degree. C.). Here, the amount of flow of the nitrogen gas was 6
liter/min. In addition, the inputted power was 84 W.
[0076] As shown in FIG. 11, the higher the temperature in the
nitrogen atmosphere became and the longer the processing time for
plasma processing became, the lower the concentration of the
endotoxin became. When the processing time for plasma processing
was approximately 7 minutes, the concentration of the ondotoxin
lowered to below 10.sup.-1 to 10.sup.0 ng/ml which is a lethal dose
for humans, and when the temperature in the nitrogen atmosphere was
73 to 83.degree. C. and the processing time for plasma processing
was 30 minutes, the concentration of the endotoxin lowered to below
10.sup.-3 ng/ml, which is the limit of detection. That is, the
plasma processing apparatus 1 of the present invention allows
endotoxins to be completely inactivated in a short period of time
at a much lower temperature than for a dry heat method, and
therefore, endotoxins sticking to the treatment object 71 can be
completely inactivated without damaging the treatment object
71.
* * * * *