U.S. patent application number 11/993362 was filed with the patent office on 2010-05-06 for method for treating plasma under continuous atmospheric pressure of work pieces, in particular, material plates or strips.
This patent application is currently assigned to SOFTAL ELECTRONIC ERIK BLUMENFELD GMBH & CO. KG. Invention is credited to Frank Forster, Peter Palm, Eckhard Prinz.
Application Number | 20100112235 11/993362 |
Document ID | / |
Family ID | 36997862 |
Filed Date | 2010-05-06 |
United States Patent
Application |
20100112235 |
Kind Code |
A1 |
Prinz; Eckhard ; et
al. |
May 6, 2010 |
METHOD FOR TREATING PLASMA UNDER CONTINUOUS ATMOSPHERIC PRESSURE OF
WORK PIECES, IN PARTICULAR, MATERIAL PLATES OR STRIPS
Abstract
The invention relates to a method for treating plasma under
continuous atmospheric pressure of, in particular, electrically
insulating workpieces, in particular material plates or strips.
According to said method, the workpiece which is to be machined, is
arranged at a distance below at least one electrode which is made
of two barrier electrodes, which are arranged in a successive
manner in the direction of displacement with a gap, and which
extends in a manner which is transversal to the direction of
displacement at least over the width of the surface of the
workpiece which is to be machined. The electrode and the workpiece
are mutually offset in the direction of displacement. High voltage,
which is in the form of an alternating voltage, is applied to the
barrier electrodes, in order to provoke at least plasma discharge
in the gap. The plasma discharge is driven by the gas flow from the
gap in the direction of the surface of the workpiece which is to be
machined. The invention is characterised in that the surfaces of
the barrier electrodes which are oriented towards the surface of
the workpiece which is to be machined are impinged upon with high
pressure.
Inventors: |
Prinz; Eckhard; (Hamfelde,
DE) ; Palm; Peter; (Hamburg, DE) ; Forster;
Frank; (Hamburg, DE) |
Correspondence
Address: |
SAND & SEBOLT
AEGIS TOWER, SUITE 1100, 4940 MUNSON STREET, NW
CANTON
OH
44718-3615
US
|
Assignee: |
SOFTAL ELECTRONIC ERIK BLUMENFELD
GMBH & CO. KG
Hamburg
DE
|
Family ID: |
36997862 |
Appl. No.: |
11/993362 |
Filed: |
June 19, 2006 |
PCT Filed: |
June 19, 2006 |
PCT NO: |
PCT/EP2006/005839 |
371 Date: |
December 20, 2007 |
Current U.S.
Class: |
427/569 |
Current CPC
Class: |
H05H 2001/2437 20130101;
H05H 1/2406 20130101; H05H 2001/2418 20130101; C23C 16/545
20130101; H01J 37/32348 20130101; C23C 16/50 20130101 |
Class at
Publication: |
427/569 |
International
Class: |
C23C 16/50 20060101
C23C016/50 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 24, 2005 |
DE |
10 2005 029 360.3 |
Claims
1. Method for continuous atmospheric pressure plasma treatment of
electrically insulated workpieces in particular, especially plates
or sheets of material, whereby a workpiece that is to be treated is
arranged at a distance beneath an electrode consisting of at least
two barrier electrodes arranged after the other in the direction of
movement, leaving a gap between them, and extending across the
direction of a movement and at least over the width of the surface
of the workpiece to be treated, and the electrode and the workpiece
are set in motion in a direction of motion in relation to one
another, with a high voltage in the form of an ac voltage being
applied to the barrier electrodes to ignite a plasma discharge at
least in the gap, and whereby a stream of gas drives the plasma
discharge out of the gap in the direction of the surface of the
workpiece to be treated, characterized in that the high voltage
acts upon the surfaces of the barrier electrodes facing the surface
of the workpiece to be treated, thereby resulting in a reduced
ignition voltage for ignition of a plasma discharge between the
surfaces of the barrier electrodes facing the workpiece and the
surface of the workpiece to be treated, said reduction in ignition
voltage being achieved because of the plasma gas flowing out of the
gap and into the area between the barrier electrodes and the
surface of the workpiece to be treated, and thereby igniting a
plasma that acts over the entire width of the workpiece.
2. The method according to claim 1, wherein chemical reagents
(precursors) are introduced into the plasma in the area between the
barrier electrodes of the surface of the workpiece to be
treated.
3. The method according to claim 1 wherein a counter-electrode is
arranged on a side of the workpiece opposite the electrode.
4. The method according to claim 1 wherein the high voltage is
generated with a symmetrical transformer with a primary coil
connected to a generator and with two secondary coils each
connected to one barrier electrode.
5. The method according to claim 1 wherein gases generated in the
area of the plasma treatment are removed by suction.
6. Method for continuous atmospheric-pressure plasma treatment of
electrically insulated workpieces in particular, especially plates
or sheets of material, whereby a workpiece to be treated is
arranged at a distance beneath a barrier electrode extending across
the direction of movement at least over the width of the surface of
the workpiece that is to be treated, and the electrode and the
workpiece are set in motion in relation to one another in a
direction of movement, whereby a high voltage in the form of an ac
voltage is applied to the barrier electrodes, characterized in that
a first space situated between the barrier electrodes and the
workpiece is filled with a first atmosphere formed by a first gas
or gas mixture, and a second space opposite the side of the
workpiece which is opposite the barrier electrode and adjacent to
the back side of the workpiece is filled with a second atmosphere
formed by a second gas or gas mixture, whereby the choice of the
high voltage and of the first and second atmospheres is made in
such a way that a plasma discharge ignites in the second atmosphere
but not in the first atmosphere.
Description
[0001] The invention relates to a method for continuous
atmospheric-pressure plasma treatment of workpieces, in particular
boards or sheets of material according to the preamble of claim 1
and/or the preamble of claim 6.
[0002] In the finishing industry or in the production of plastic
films, the film is activated at the surface by a plasma treatment
at atmospheric pressure, also known as a corona treatment. An
industrial corona system usually comprises a high-voltage electrode
and a counter-electrode designed as a roll which is guided over the
plastic film in close proximity thereto. The electrode is arranged
parallel to the roll, the electrode being connected to a high
voltage of approx. 10 kilovolts at approx. 20-40 kilohertz and the
roll being connected to ground potential. Due to the potential
difference in the air gap between the high-voltage electrode and
the roll with the plastic film, amounting to a few millimeters, a
corona discharge develops with a conventional practical power
output of 1 to 5 kilowatts per meter. The plastic film is activated
by the corona discharge, i.e., oxidized at the surface.
[0003] Due to this activation, the surface tension is increased to
thereby ensure adequate adhesion of printing inks and
adhesives.
[0004] With the device described above, thin plastic films can be
treated, but materials greater than 6 mm in thickness such as foam,
plastic sheeting, plastic sections several centimeters thick or
even wooden boards of similar thicknesses cannot be treated in this
way. The reason for the restriction is the unequal development of
the discharge channels with an increase in the electrode gap which
thus results in an irregular activation of the surface of the
material.
[0005] DE 102 28 506 A1 discloses a method for continuous
atmospheric pressure plasma treatment of electrically insulated
workpieces that operates by a different principle, but this method
includes all of the features of the preamble of claim 1. Thus two
barrier electrodes arranged with a distance between them are used
here, a plasma discharge is ignited in the gap formed between the
barrier electrodes and is then expelled by a gas stream in the
direction of the surface to be treated.
[0006] In the method disclosed in the aforementioned publication,
the plasma acts only along a narrow strip, the width of which
corresponds essentially to the width of the gap left between the
barrier electrodes on the surface of the workpiece to be
treated.
[0007] Against this background, the present invention describes a
method with which a workpiece can be subjected to an atmospheric
pressure plasma treatment continuously along a larger working
width.
[0008] A first possibility for such a method is defined in claim 1,
this method being based on the method disclosed in DE 102 28 506
A1.
[0009] An alternative possibility for such a method is described in
claim 6.
[0010] Advantageous refinements of the method according to claim 2
are specified in greater detail in the dependent claims 2 through
5.
[0011] The electrode consists of at least two barrier electrodes
but more than two barrier electrodes may also be aligned in rows
one after the other, leaving a gap after each.
[0012] The surfaces of the barrier electrodes facing the surface of
the workpiece to be treated is acted upon by the high voltage.
Therefore, due to the effect described above, a plasma discharge is
ignited over the entire width of the surface of the workpiece to be
treated, this plasma discharge being made possible by the ignition
voltage which is reduced, due to the plasma species present in the
space between the electrode and the workpiece because of the plasma
gas expelled from the gap, thus allowing treatment of the surface
of the workpiece over its entire width. This phenomenon is referred
to here as "capacitive coupling discharge."
[0013] According to a simple variant, the electrode is composed of
two single channel barrier electrodes. According to this invention,
as the workpiece approaches the electrode, capacitive coupling
occurs due to the dielectric mass of the workpiece as the workpiece
is brought to an adjusted distance in proximity to the electrode
with a suitable choice of the other parameters (high voltage,
atmosphere). Due to the presence of the plasma species formed in
the gap between the barrier electrodes and driven out of the gap in
the direction of the workpiece surface, a uniform discharge
therefore develops between the barrier electrodes and the workpiece
resembling a glow discharge in a vacuum plasma. The electrode is
operated mainly with air as the process gas, but it may also be
operated in foreign gas atmosphere, e.g., in nitrogen or mixtures
of nitrogen with other gases such as oxygen, carbon dioxide,
hydrogen or noble gases. Due to the discharge, the workpiece
surface is oxidized, depending on the type of gas, and/or other
chemical groups, e.g., amines, amides or imides are incorporated.
Therefore, the surface energy of the workpiece is increased and
thus the adhesion of paints, enamels, adhesives or other coatings
is improved or made possible. An advantage of this inventive method
is in particular the fact that due to the capacitive coupling, the
discharge is adapted to the dimensions of the workpiece, i.e., the
discharge is ignited primarily on the workpiece surface but not
beside it. This results in a location-specific discharge and also
leads to savings of the energy required for igniting and
maintaining the discharge.
[0014] The gap between the barrier electrodes is preferably between
0.5 millimeter and 5 millimeters wide. Gaps of these widths are
especially suitable for ignition of the desired plasma with the
voltage ranges preferred for performing this method.
[0015] The barrier electrodes are preferably made of aluminum oxide
ceramic. This material is especially resistant.
[0016] The barrier electrodes are made of rectangular tubes each
having one or more channels.
[0017] The barrier electrodes are preferably arranged on a holding
body. However, the barrier electrodes may also be attached to a
holding plate by means of electrode carriers via insulators. By
sealing off the design space between the barrier electrodes and the
holding plate, in this case a chamber is formed into which air or
another gas can be fed, to then flow through the gap as a result of
the excess pressure which then builds up and to drive the discharge
out of the gap in the direction of the workpiece.
[0018] With a process management according to claim 2, an
additional coating of the workpiece surface with chemical compounds
formed from the precursors in the plasma can be achieved.
[0019] According to a refinement of the present invention, a
counter-electrode is arranged as described in claim 3. The
counter-electrode may be formed preferably as a supporting surface
designed as an electrode. In the case of thick insulating materials
such as sheets, sections, hollow chamber sections, web plates,
etc., the counter-electrode may be omitted. Materials having a low
dielectric mass such as plastic films, foams, air cushion film,
paper, plastic fibers or natural fibers, granules or powders should
be treated with a counter-electrode. The counter-electrode may
serve as a dielectric mass (roller, conveyor belt) and/or as a
ground metal roll or plate with a dielectric (silicone or ceramic)
or may be designed without a dielectric. In the case of a
dielectric roll, treatment of the back side is prevented or greatly
suppressed in treatment of plastic films when there are
indentations in the roll in the case of a dielectric roll with a
capacitive coupling discharge. A counter-electrode can also be an
electrode designed in mirror image to the electrode producing the
discharge. Then the workpiece is passed between two electrodes.
This also allows two-sided treatment of the substrate.
[0020] To create a high voltage as is necessary for ignition of the
plasma discharge, preferably a symmetrical transformer with a
primary coil connected to a generator and with two secondary coils
each connected to one of the barrier electrodes is used (claim 4).
Instead of operation with one shared transformer, operation with
two separate transformers is also possible. They may be operated in
synchronized operation or in push-pull operation.
[0021] In the case of electrically conductive materials such as
metallized plastic films, the high voltage is reduced to one-half
by a symmetrical transformer. This prevents damage to the thin
metal layer by the plasma discharge.
[0022] To be able to reliably divert the ozone and other byproducts
formed in the plasma discharge from the processing site, the
electrode is preferably arranged in a tunnel-like housing that is
open on the side facing the top side of the workpiece and the
housing is connected to a suction exhaust (see claim 5).
[0023] An alternative method which solves the same problem as
described above does not rely on a refinement of the state of the
art according to DE 102 28 506 A1, but instead uses an alternative
approach. This method is characterized in claim 6.
[0024] The essential invention of the method here consists of
controlling the ignition of plasma in a certain range through the
type of atmosphere in this area and adjusting a suitable
high-voltage accordingly. In this variant, a plasma should be
ignited only on the side of the sheet or board of material that is
opposite the electrode. To do so, in the area between the electrode
and the first side of the workpiece, a first atmosphere is
established in which a plasma does not yet ignite at a selected
high voltage. On the opposite side of the sheet of material, a
second atmosphere differing from the first atmosphere is
established in which a plasma ignition can already take place,
induced by the high voltage applied by the electrode. Thus in a
targeted manner, a plasma is ignited only on the "back side" of the
sheet or board of material so that a large area plasma treatment is
performed there. Here again, this is a "capacitively coupling
discharge" in the sense of the present invention, with the
discharge also over the entire width and length of the electrodes
in this example, but limited to the dimensions of the respective
material to be treated.
[0025] Additional advantages and features of the invention are
derived from the following description of the invention on the
basis of exemplary embodiments depicted in the figures, in
which
[0026] FIG. 1 shows a schematic side view of a device for
performing the inventive method in a first variant, this view
showing the direction of conveyance of a workpiece that is to be
coated continuously;
[0027] FIG. 2 shows a basic diagram of the electric wiring of the
electrode of the device shown in FIG. 1;
[0028] FIG. 3 shows a schematic view in the direction of movement
of the workpiece to be coated showing a detail of the device with
the plasma ignited;
[0029] FIGS. 4a and 4b show two possible wiring variants of an
alternative embodiment of an electrode with two double-channel
barrier electrodes;
[0030] FIG. 5 shows another possible wiring of two double-channel
barrier electrodes, a precursor additionally being fed into the
ignited plasma discharge in this case and
[0031] FIG. 6 shows a schematic diagram of an inventive method
according to the second variant.
[0032] In the figures, the same or similar elements are labeled
with the same reference numerals.
[0033] FIG. 1 shows schematically a first cross section through a
device for performing the inventive method according to the first
alternative, this cross section being shown along a plane in which
the direction of movement occurs. The inventive device consists of
two barrier electrodes 1a, 1b arranged one after the other in the
direction of movement (arrow P) of a workpiece 13. A gap 12 is left
between the barrier electrodes 1a, 1b. The barrier electrodes 1a,
1b are arranged on a holding body 2 which at the same time forms a
chamber for introducing a gas 11, preferably air or nitrogen and/or
a gas mixture containing nitrogen to drive this gas and/or gas
mixture through the gap 12 in the direction of the surface of the
workpiece 13 to be treated. A plasma ignited in the gap 12 between
the barrier electrodes 1a, 1b is conveyed through the gas and/or
gas mixture constantly being resupplied into the gap and the plasma
is conveyed into the area between electrodes 1a, 1b and the
workpiece 13, ultimately flowing out of this area in both
directions, namely with and against the direction of movement
(arrow P). A tunnel-shaped housing 9 which is open in the direction
of the workpiece 13 is arranged above the arrangement of the
holding body 2 and the electrode (barrier electrodes 1a, 1b) and
this housing is connected via an upper opening to a suction device
10, shown here schematically. The workpiece 13 is conveyed in the
direction of movement (arrow P) by mechanisms that are not shown
here. To this end the workpiece may rest on a supporting surface
(e.g., a conveyor belt), for example, but it may also be conveyed
away beneath the electrode without a supporting surface due to its
own inherent rigidity. An electric conductor 3, shown here
schematically, runs in the barrier electrodes 1a, 1b, which in the
present case are rectangular tubes made of aluminum oxide ceramic,
to make it possible to apply an appropriate voltage to the
respective barrier electrode 1a, 1b. The barrier electrodes 1a, 1b
in this exemplary embodiment have a length of up to several meters.
The electric conductor 3 may be comprised of, for example, a metal
powder filling or a metal coating of the electrode from the
inside.
[0034] FIG. 2 shows schematically an electric wiring of the barrier
electrodes 1a, 1b. To supply high voltage to the barrier electrodes
1a, 1b, the device has a transformer, which is indicated here by
the border labeled as 5 and which in this case is a symmetrical
transformer having a primary coil 8 and two secondary coils 6. The
secondary coils 6 are each connected to one of the barrier
electrodes 1a, 1b and to ground 15. The connection to the electric
mass 15 may also be omitted. An alternating voltage generator 7 is
connected to the primary coil 8 of the transformer 5. The voltage
may be wired in synchronized operation or in push-pull
operation.
[0035] In this example, a sinusoidal voltage between 10 and 60
kilovolts with a frequency of 1 to 100 kilohertz, preferably 5 to
30 kilohertz is used. The voltage may also be pulsed. Due to the
symmetrical transformer, the voltage is applied uniformly to the
two barrier electrodes 1a, 1b so that a plasma can be ignited in
the gap 12. The gap 12 has a gap width of 0.5 to 5 millimeters,
preferably 1 millimeter. Due to the flow of the gas 11 into the gap
12 and/or through the gap in the direction of the surface of the
workpiece 13, the ignited plasma 4 is conveyed in the direction of
the surface of the workpiece 13 that is to be treated. In the
plasma gas, the ignition voltage is reduced. Therefore, in approach
of the workpiece 13 to a distance of 1 millimeter to 20 millimeters
from the electrodes, there is a capacitive coupling due to the
dielectric mass of the workpiece 13 and thus a uniform discharge 4
developments between the surface of the workpiece 13 that is to be
treated and the facing surfaces of the barrier electrodes 1a, 1b.
This discharge is like a glow discharge in a vacuum plasma. Due to
the capacitive coupling, the discharge 4 is adapted in its
dimensions to the dimensions of the workpiece, i.e., the discharge
4 ignites primarily on the workpiece surface and not beside it.
This is indicated schematically in FIG. 3, which is a schematic
view of one of the barrier electrodes 1a and the workpiece 13 which
is guided beneath a view as seen in the direction of movement
(arrow P).
[0036] During operation of the device, the workpiece 13 has been
moved beneath the electrodes formed by the two barrier electrodes
1a, 1b so that a continuous plasma treatment of the surface of the
workpiece 13 facing the electrode can be achieved along its entire
width.
[0037] Due to the gas 11 (e.g., air) which is supplied via the
holding body 2, not only is the discharge deflected out of the gap
12 in the direction of the surface of the workpiece 13 that is to
be treated, but at the same barrier electrodes 1a, 1b are also
cooled.
[0038] The thermal stress on the workpiece to be treated is low.
After a treatment with the device depicted in FIG. 1, an increase
in temperature of only approx. 5.degree. C. is found.
[0039] In addition to an electric wiring for a so-called
capacitively coupling discharge, like that shown in FIG. 2, in
which the discharge is deflected onto the side facing the workpiece
and takes place between the surface of the workpiece 13 to be
treated and the entire surface of the electrode facing the surface
of the workpiece 13 to be treated, other possible operating modes
of an inventive device may also be considered.
[0040] With a modified device that has a double-channel tube
instead of each of two simple rectangular tubes as barrier
electrodes 1a, 1b, capacitively coupling discharges can be achieved
(see FIGS. 4a and 4b).
[0041] In these cases, the barrier electrodes 1 are implemented by
two double-channel tubes, each being equipped with conductors 3.
The barrier electrodes are either connected to the symmetrical
transformer in parallel, as illustrated in FIG. 4a, or in an
antiparallel (FIG. 4b). In the case of an antiparallel connection,
there is a higher energy input due to the higher field line density
of the electric field in the gap between the barrier electrodes 1a,
1b. Due to preionization of the discharge carriers in the gap 12,
the remote effect of the charge carriers leaving the electrode in
the direction of the workpiece 13 may be expanded in comparison
with the arrangement having two single channel barrier electrodes
(FIG. 1). Thus a linear plasma free jet develops, in particular
when there is a great distance from the workpiece, which depends on
the size of the dielectric mass. In an approach of the workpiece 13
to the electrode, the discharge 4 according to this invention is
pulled toward the workpiece 13 by capacitive coupling.
[0042] FIG. 5 shows another variant where so-called precursors 14
are fed into the plasma discharge for deposition of layers on the
workpiece 13. Such precursors 14 may be, for example,
tetramethylorthosilicate, hexamethylene disiloxane in the form of
vapor or aerosols. With the aforementioned precursors 14, a silicon
dioxide layer, for example, in the range of a few nanometers to
micrometers may be deposited on the surface of the workpiece. With
the capacitively coupling discharge, a precursor current like that
described here may be fed preferably into the capacitively coupled
discharge zone between the surface of the workpiece 13 that is to
be treated and the surfaces of the barrier electrodes 1a, 1b facing
the surfaces of the workpiece 13 that is to be treated.
[0043] It is important for the precursors 14 not to be fed between
the electrodes, which are connected to the high voltage, in order
to prevent the latter from being coated.
[0044] Finally, FIG. 6 shows schematically how an inventive method
is performed according to the claimed alternative.
[0045] This shows how an electrode, which in this case is made up
of a double-channel barrier electrode 1a, 1b, is arranged on one
side of a workpiece 13 (a sheet or panel of material) and a housing
9 is arranged on the opposite of the workpiece 13 with respect to
the electrodes 1a, 1b. An atmosphere fed into the housing 9 is such
that, when an ac high voltage is applied to the electrodes 1a, 1b,
this atmosphere allows ignition of a plasma discharge 4 on this
side of the workpiece 13, with a different accordingly prevailing
in the area between the electrodes 1a, 1b and the workpiece 13 to
suppress a plasma discharge. In this way the workpiece 13 is coated
over a large area of the "back side" which is opposite the
electrodes 1a, 1b. The atmosphere in the housing 9 is also removed
by suction in this method to prevent unwanted plasma products,
especially ozone, from entering the environment. This figure
additionally shows how precursors 14 are introduced into the area
of the plasma discharge 4. This is possible but not necessary for
the inventive method. This method functions equally well without
the introduction of precursors.
[0046] The electrodes 1a, 1b may also be, for example, an electrode
formed by two individual barrier electrodes separated from one
another by a gap (an electrode pair). As long as the gap is not too
great, a continuous plasma discharge will still develop on the side
of the workpiece 13 facing the housing 9, producing a desired
surface change on this side of the workpiece.
[0047] Other possible applications are conceivable, for example,
for internal treatment and/or internal coating of planar
three-dimensional components, where electrically insulated
workpieces having multiple channels are treated and coated in the
interior. This is done by passing a noble gas such as argon through
the channels, thereby lowering the ignition voltage according to
Paschen's law so that the discharge is ignited in the interior. As
already described above, the capacitively coupling discharge is
ignited mainly on the workpiece and not in the gas space beside it
and therefore is ignited mainly in the channels of the workpiece.
If the carrier gas stream is provided with the vapor and/or aerosol
of a precursor, then layers are deposited in the channels. In the
treatment, the workpiece lies on a counter-electrode. Instead of
the pure noble gas, mixtures with air, nitrogen, oxygen and the
like may also be used.
[0048] Furthermore, a capacitive coupling may be performed in a
large volume reaction chamber. The plasma discharge is ignited
throughout the entire chamber in the case of a large volume chamber
through which a noble gas flows, by attaching the barrier
electrodes through the capacitive coupling described above.
Depending on the size of the chamber, several electrodes may be
necessary. Instead of a pure noble gas, mixtures with air and
nitrogen, oxygen and the like may again be used here. Here again,
precursors may be added to the carrier gas in the case when coating
is desired.
[0049] In this reaction, it is also conceivable to treat melts on
an extruder. Polymer melts can also be treated with a capacitively
coupling discharge shortly after discharge from an extruder nozzle
to thereby ensure adhesion to a web to be coated.
[0050] It is also possible with the inventive device and/or with
the inventive method to activate liquids in the mode of the
capacitively coupling plasma discharge. Then chemical reactions may
be induced at the plasma-liquid interface, their products then
being able to diffuse into the liquid. It is also possible to
crosslink thin liquid films by using a plasma discharge according
to this invention.
[0051] Description of Treatment Example:
[0052] 1. Treatment not Including the Back Side by Capacitively
Coupling Discharge
[0053] An LDPE film with a surface energy (before the plasma
treatment) of 30 mN/m on both sides was plasma treated on the side
facing the barrier electrodes. The LDPE film was freely clamped,
i.e., no counter-electrode was used. The plasma treatment was
performed with a pair of electrodes according to FIG. 4a, formed by
a double-channel tube and arranged in parallel with one another
from a distance of 0.5 mm leaving a gap. The film was moved at the
rate of 60 m/min beneath the electrode using a linear table, where
the distance from the barrier electrodes to the LDPE film was 1.5
mm.
[0054] An electric energy of 500 watts was applied to the double
barrier electrode at a frequency of the ac high voltage of 8
kilohertz. Blowing air was fed into the gap between the two
double-channel tubes of the double barrier electrodes at
essentially atmospheric pressure. Under the aforementioned boundary
conditions, the plasma between the barrier electrodes ignited and
was expelled by the blowing air onto the LDPE film. The ignition
voltage in this range was reduced due to the plasma species blown
out into the interspace between the double barrier electrode and
LDPE film to such an extent that a "secondary ignition" of a large
area plasma was ignited in the entire area between the surfaces of
the barrier electrodes facing the surface of the LDPE film and the
surfaces facing the film (remote discharge). Ten treatments were
performed in this way.
[0055] The surface energy was measured with test inks according to
the DIN ISO 8296.
[0056] On the basis of the plasma treatment described above, on the
barrier electrode side of the LDPE film, an increase in the surface
energy to 42 mN/m could be achieved through a capacitively coupling
discharge; this is a typical value for a print pretreatment. The
surface energy on the side of the LDPE film facing away from the
barrier electrodes (back side of the film) still amounted to 30
mN/m. Thus, no treatment has taken place here.
[0057] 2. Treatment of Web Plates
[0058] A 7.5 mm thick polypropylene web plate with a surface energy
(before the plasma treatment) of 30 mN/m on both sides was plasma
treated on the side facing the barrier electrodes. This was done by
freely clamping the polypropylene web plate, i.e., no
counter-electrode was used.
[0059] The plasma treatment was performed with a pair of
double-channel tubes according to FIG. 4a arranged at a distance of
0.5 mm in parallel with one another while leaving a gap.
[0060] The web plate was moved beneath the electrode system using a
linear table at the rate of 10 m/min.
[0061] The electric energy applied to the double barrier electrode
was 500 watts at a frequency of the ac high voltage of 8 kilohertz.
The distance between the barrier electrodes and the web plate was
1.0 mm. Blowing air was fed into the gap between the two
double-channel tubes of the double barrier electrodes.
[0062] Under the boundary conditions defined above, the plasma
ignited between the barrier electrodes and was expelled onto the
web plate by the blowing air. The ignition voltage was reduced in
this area due to the plasma species blown out into the interspace
between the double barrier electrodes and the web plate until a
"secondary ignition" of a large area plasma was ignited in the
entire area between the surfaces of the barrier electrodes facing
the plate and the surface of the web plate (remote discharge). Two
treatments were performed.
[0063] The surface energy is measured with test inks according to
DIN ISO 8296.
[0064] This plasma treatment resulted in an increase in the surface
energy to 50 mN/m owing to the capacitively coupling discharge on
the barrier electrode side of the polypropylene web plate; this is
a typical value for adhesive bondability. The back side of the web
plate did not receive any treatment and the value of the surface
energy remained at the original level of 30 mN/m.
LIST OF REFERENCE NOTATION
[0065] 1a, b Barrier electrode
[0066] 2 Holding body
[0067] 3 Electric conductor
[0068] 4 Plasma discharge
[0069] 5 Transformer
[0070] 6 Secondary coil
[0071] 7 Generator
[0072] 8 Primary coil
[0073] 9 Housing
[0074] 10 Suction
[0075] 11 Gas
[0076] 12 Gap
[0077] 13 Workpiece
[0078] 14 Precursor
[0079] 15 Electric mass
[0080] P Arrow
* * * * *