U.S. patent application number 12/468660 was filed with the patent office on 2009-09-17 for method and device for microwave plasma deposition of a coating on a thermoplastic container surface.
This patent application is currently assigned to SIDEL. Invention is credited to Yann Pernel, Jean-Michel RIUS.
Application Number | 20090229521 12/468660 |
Document ID | / |
Family ID | 32309790 |
Filed Date | 2009-09-17 |
United States Patent
Application |
20090229521 |
Kind Code |
A1 |
RIUS; Jean-Michel ; et
al. |
September 17, 2009 |
METHOD AND DEVICE FOR MICROWAVE PLASMA DEPOSITION OF A COATING ON A
THERMOPLASTIC CONTAINER SURFACE
Abstract
The deposition of a coating on a thermoplastic container surface
using low pressure plasma by excitation of a precursor gas with UHF
electromagnetic waves in a circular shaped vacuum cavity receiving
the container is provided. It includes dimensioning the cavity with
respect to the frequency of the UHF electromagnetic waves so as to
obtain a coupling mode generating several electromagnetic fields
inside the cavity. In particular a TM 120 coupling mode is provided
which generates two central fields (4.sub.A, 4.sub.B) inside the
cavity, whereby two containers can be simultaneously treated in
said cavity.
Inventors: |
RIUS; Jean-Michel;
(Octeville sur Mer, FR) ; Pernel; Yann; (Octeville
sur Mer, FR) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 PENNSYLVANIA AVENUE, N.W., SUITE 800
WASHINGTON
DC
20037
US
|
Assignee: |
SIDEL
Octeville Sur Mer
FR
|
Family ID: |
32309790 |
Appl. No.: |
12/468660 |
Filed: |
May 19, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10536902 |
May 27, 2005 |
|
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PCT/FR2003/003485 |
Nov 25, 2003 |
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12468660 |
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Current U.S.
Class: |
118/723MW |
Current CPC
Class: |
C23C 16/511 20130101;
H01J 37/32192 20130101; H05H 1/46 20130101; H05H 2001/4622
20130101; H01J 37/32366 20130101; C23C 16/045 20130101 |
Class at
Publication: |
118/723MW |
International
Class: |
C23C 16/511 20060101
C23C016/511 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 28, 2002 |
FR |
0214961 |
Claims
1.-2. (canceled)
3. A device for depositing a coating on one face of at least one
container made of a thermoplastic using a low-pressure plasma by
excitation of a precursor gas by UHF electromagnetic waves in a
circular vacuum chamber containing said container, which device
comprises a UHF wave generator and a UHF waveguide for connecting
said generator to a window of a side wall of the chamber, wherein
the chamber is sized in relation to the frequency of the UHF
electromagnetic waves in order to establish a TM 120 coupling mode
that generates two central fields in the cavity, whereby it is
possible for two containers to be simultaneously treated inside
said chamber.
4. The device as claimed in claim 3, wherein the generator emits an
electromagnetic wave having a frequency f=2.455 GHz and in that the
diameter of the chamber is approximately 273 mm.
5. The device as claimed in claim 3, wherein said chamber contains
two quartz envelopes amounted in a vacuum-tight manner in the
chamber and placed respectively substantially coaxial with the two
central fields, wherein said chamber includes a single window for
injecting the UHF waves, said window being located along the axis
of symmetry of the two central fields, and wherein a single cover
for closing off said chamber is equipped with a single coupler for
connection to a vacuum source, which coupler is divided into two in
order to be connected to said two respective envelopes, with two
precursor gas injectors that are connected to a single precursor
gas source and with two support means for the two respective
containers.
6. The device as claimed in claim 5, wherein the device includes
positionally adjustable bottom and top plates suitable for acting
on the respective return fields so as to refine the coupling in
relation with various types of container to be treated.
7. The device as claimed in claim 5, being designed for coating the
inside of containers and wherein for this purpose, the precursor
gas injectors are designed to sit inside the respective containers
when said containers are supported by support means in the
envelopes.
Description
[0001] The present invention relates to improvements made in the
field of the deposition of a coating on a face of a thermoplastic
container using a low-pressure plasma by excitation of a precursor
gas by UHF electromagnetic waves in a circular vacuum chamber (or
reactor) containing said container.
[0002] The invention applies more particularly to a deposition of a
barrier layer inside bottles or pots made of a thermoplastic, such
as PET, so as to improve the gas barrier properties, with regard to
internal gases or external gases, and possibly to improve the
isolation from the outside of the product with which said bottles
or pots are filled.
[0003] A device for depositing such a coating using a low-pressure
plasma by excitation of a precursor gas by means of UHF
electromagnetic waves has been described and illustrated in
document FR 2 799 994. The UHF generator is connected to the
chamber via a UHF waveguide, which runs into a window of the side
wall of the chamber, with a TM 020 coupling mode that generates an
axial central field in the chamber. To undergo the treatment
envisioned, the container to be treated is therefore placed at the
center of the chamber in a quartz envelope coaxial with the
chamber.
[0004] In an industrial production machine, several (typically 20)
devices are joined together on a rotating structure capable of
treating about 10,000 bottles per hour.
[0005] These machines are satisfactory as regards the quality of
the containers obtained.
[0006] However, there is a keen interest for users to have a higher
treatment rate.
[0007] An increase in rate could admittedly be achieved by
installing a larger number of devices on the rotating structure.
However, this increase in the number of devices could be rendered
possible only by increasing the dimensions of the rotating
structure. This would result in a larger, heavier and therefore
more expensive machine, which is unacceptable.
[0008] Likewise, the operation of a second machine running in
parallel with the first would admittedly allow the rate to be
doubled, but here again this would result in bigger space required
and a higher cost, which are unacceptable.
[0009] The object of the invention is consequently to improve the
existing devices, leading to a machine that is more efficient in
terms of production while still maintaining acceptable size and an
acceptable cost.
[0010] For this purpose, according to a first of its aspects, the
invention proposes a method for depositing a coating on one face of
a container made of a thermoplastic using a low-pressure plasma by
excitation of a precursor gas by UHF electromagnetic waves in a
circular vacuum chamber containing said container, which method is,
according to the invention, characterized in that the chamber is
sized in relation to the frequency of the UHF electromagnetic waves
so as to obtain a coupling mode that generates several
electromagnetic fields inside the chamber, whereby it is possible
for several respective containers to be simultaneously treated in
the same chamber. In a preferred embodiment, a TM 120 coupling mode
is established, which generates two symmetrical fields inside the
chamber, these fields themselves having two separate energy
regions, whereby it is possible for two containers to be
simultaneously treated in said chamber, this method offering the
advantage of being able to be implemented in a simple manner in
conjunction with commercially available magnetrons operating at a
frequency of 2.455 GHz.
[0011] Thus, thanks to the method of the invention, it is possible
to double the container treatment rate solely by an arrangement of
the currently known means, and therefore relatively
inexpensively.
[0012] According to a second of its aspects, the invention
proposes, for implementing the aforementioned method, a device for
depositing a coating on one face of a container made of a
thermoplastic using a low-pressure plasma by excitation of a
precursor gas by UHF electromagnetic waves in a circular vacuum
chamber containing said container, which device comprises a UHF
wave generator and a UHF waveguide for connecting said generator to
a window in the side wall of the chamber, which device, being
designed in accordance with the invention, is characterized in that
the chamber is sized in relation to the frequency of the UHF
electromagnetic waves in order to establish a TM 120 coupling mode
that generates two symmetrical fields in the cavity, these fields
themselves having two separate energy regions, whereby it is
possible for two containers to be simultaneously treated in said
chamber.
[0013] In a preferred practical embodiment, the generator emits an
electromagnetic wave having a frequency f=2.455 GHz and the
diameter of the chamber is approximately 273 mm. The generator is a
magnetron commonly employed in other fields. As regards the
diameter of the chamber, this is perfectly compatible with the
structures of the current machines. It therefore proves possible,
through a simple modification of the current machines, to double
the treatment capacity of the machines, since the diameter of the
chamber permits simultaneous treatment of two bottles of half-liter
or smaller size placed side by side in the respective two central
fields.
[0014] Particularly advantageously, the chamber contains two quartz
envelopes placed respectively so as to be approximately coaxial
with the two abovementioned symmetrical fields, the chamber
includes a single window for injecting the UHF waves, the window
being located symmetrically straddling the plane of symmetry on
each side of which the two central fields are situated, and a
single cover for closing off the chamber is equipped with a single
coupler for connection to a vacuum source, which is divided into
two in order to be connected to the abovementioned two respective
envelopes, with two precursor gas injectors that are connected to a
single precursor gas source and with two support means for the two
respective containers, in such a way that using the provisions of
the invention does not entail having to duplicate the necessary
equipment (such as pressure sensors on the inside and the outside
of the container).
[0015] It is advantageous for the device to also include bottom and
top plates, the position of each of which can be adjusted, these
plates being suitable for acting on the respective return fields so
as to refine the coupling according to the various types of
container that can be treated.
[0016] Within the context of the specifically preferred application
envisioned, the device is designed for coating the inside of
containers and for this purpose, the precursor gas injectors are
designed to sit inside the respective containers when the latter
are supported by the support means in the envelopes.
[0017] The invention will be more clearly understood on reading the
detailed description that follows of a preferred embodiment, most
particularly suitable for coating the inside of containers, and
given solely by way of nonlimiting example. In this description,
reference will be made to the appended drawings in which:
[0018] FIG. 1 is a diagram illustrating the conditions under which
the method of the invention are carried out; and
[0019] FIG. 2 is a schematic representation of a device for
implementing the method of the invention.
[0020] FIG. 1 shows schematically a chamber 1 having the general
shape of a cylinder of revolution, which has, in its side wall, an
opening 2 through which a waveguide connected to a UHF
electromagnetic wave generator (not shown) enters.
[0021] The UHF generator is a magnetron operating at a frequency of
2.455 GHz.
[0022] In order to be able to treat several containers 3 (the two
containers 3 are shown schematically in dotted lines)
simultaneously in the chamber 1, the dimensions of the chamber are
chosen in relation to the frequency of the UHF electromagnetic
waves, so as to obtain a coupling mode that generates several
electromagnetic fields inside the chamber, each container 3 being
placed coaxially in a respective field.
[0023] In one practical embodiment of this arrangement, a TM 120
coupling mode is established, which generates two symmetrical
electromagnetic fields, these fields themselves having two separate
energy regions, namely two central fields 4.sub.A and 4.sub.B and
two return fields 5.sub.A, 5.sub.B located peripherally, in the
shape of haricot beans, facing the inner fields, as illustrated in
FIG. 1. The two containers 3 to be treated are placed coaxially in
the respective central fields 4.sub.A, 4.sub.B. It is also
desirable for the positionally adjustable bottom 17.sub.i and top
17.sub.s plates (visible in FIG. 2) to act on the return field
5.sub.A, 5.sub.B in order to refine the coupling to the reactor
according to the various types of container 3 capable of being
treated.
[0024] Under these conditions, the cut-off wavelength is given
by:
.lamda. c = 2 .pi. R U 12 ##EQU00001##
where R is the radius of the chamber and U.sub.12 characterizing
the T.sub.120 mode has a value U.sub.12=7.0156.
[0025] The cut-off wavelength .lamda..sub.c has a value close to
(but slightly greater than) the wavelength .lamda. of the
generator:
.lamda. = v f = 3 .times. 10 3 2 , 455 .times. 10 3 = 12 , 22 cm
.fwdarw. .lamda. c # 12 , 225 cm ##EQU00002##
[0026] The radius R of the chamber is:
R = .lamda. c .times. U 12 2 .pi. = 12.225 .times. 7.0156 2 .pi. =
13.65 cm . ##EQU00003##
[0027] The chamber therefore has to have a diameter of
approximately 273 mm.
[0028] The diameter of the chamber 1 thus formed allows two
containers, such as two bottles 50 cl in volume or less to be
treated simultaneously. By operating in this manner, the treatment
capacity of each chamber is doubled. This makes it possible to
meet, very favorably, the requirements of users while still
maintaining a chamber having dimensions compatible with the
rotating structures currently used. In other words, the
arrangements according to the invention may be implemented without
it being necessary to redesign the entire rotating structure.
[0029] FIG. 2 illustrates, in side view, a container treatment
device produced around the chamber 1 shown schematically in FIG.
1.
[0030] The device shown in FIG. 2, denoted in its entirety by the
numerical reference 6, includes a cavity (or reactor) 1 which is a
cylinder of revolution having a diameter of approximately 273 mm.
The side wall of the chamber 1 has, approximately at mid-height, an
opening 2 through which a waveguide (not shown) enters, said
waveguide being connected to a UHF generator 7 (largely concealed
by the chamber), for example formed by a magnetron, capable of
operating at the frequency of 2.455 GHz. This device generates a TM
120 coupling mode with two central fields as illustrated in FIG. 1,
these two central fields being centered on the axes A and B shown
in FIG. 2.
[0031] The arrangement of the device is transposed from that of a
device for treating a single container, as described and shown in
particular in the abovementioned document FR-A-2 799 994. In
particular, two quartz envelopes 8 are placed in the chamber,
coaxially with the axes A and B, and inside which envelopes the two
respective containers 3 are placed. These two envelopes 8 are
mounted in a vacuum-tight manner (with seals 18) in the chamber,
each envelope defining a cavity of small volume in which the
container may be placed and making it easier to create the vacuum
required by the generation of the plasma necessary for depositing
the coating in each container.
[0032] However, one advantage of the arrangement adopted lies in
the fact that the device still requires just one superstructure. In
other words, the single cover 9 for the chamber incorporates, on
the one hand, the members 10 for supporting the two containers 3
and, on the other hand, the connection means needed for creating
the vacuum in the chamber and for injecting the precursor gas
needed to form the plasma, and also the internal pressure sensor
and the external pressure sensor.
[0033] Thus, the cover 9 is provided with an enclosure 10 connected
(via a line, not shown in FIG. 2) to a vacuum source, which
enclosure 10 extends above the two containers 3 and is in
communication at 11 with the inside of the containers. In the
example shown, the passage 11 is combined with the means 12 for
supporting each container 3.
[0034] According to the preferred way of implementing the invention
for coating the inside of containers, each passage 11 is penetrated
coaxially by a precursor gas injector 13 which sits inside the
corresponding container 3. The two injectors 13 may be connected,
on the outside of the cover 9, to a single line 14 for connection
to a source (not visible in the figures) of precursor gas.
[0035] The cover 9 may furthermore be equipped with a valve 15 for
bringing the enclosure 10 into communication with ducts 16, either
for bringing the inside of the containers 3 into communication with
the inside of the envelopes 8 while the vacuum is being created, or
for isolating them so as to be able to create differential pressure
conditions suitable for generating a plasma in the containers.
[0036] In total, the provisions according to the invention, which
consist in establishing a TM 120 coupling mode in order to be able
to treat two containers simultaneously, prove to be beneficial in
the sense that while admittedly it is necessary to duplicate all
the elements that cooperate directly with the two containers (i.e.
two quartz envelopes, two injectors, two support means, two vacuum
orifices), the remainder of the installation nonetheless remains
common (i.e. one single cavity, one single UHF generator, one
single source and one single feed for the vacuum, one single source
and one single feed for the precursor gas, one single internal
pressure sensor, one single external pressure sensor, one single
cover and therefore one single mechanism for actuating
(lowering/raising) the cover, a single mechanism for gripping the
containers, in order to hold them in place and for removing them,
etc.).
[0037] In addition, since there is only one cover 9, there remain
only single means for actuating said cover, in order to close/open
the chamber 1, such as those mentioned in document FR-A-2 799
994.
[0038] In general, the arrangement of the chamber 1 must comply
with the symmetry provided by the two central fields 4.sub.A,
4.sub.B. In particular, the window 2 through which the waveguide
enters the chamber 1 is placed on the axis between the two central
fields 4.sub.A, 4.sub.B, as may be seen in FIGS. 1 and 2. Likewise,
columns for supporting the impedance-matching plates 17.sub.i,
17.sub.s for the respective external fields 5.sub.A, 5.sub.B (these
columns not being shown in order not to clutter up the drawings;
see for example document FR-A-2 792 854) must be placed
symmetrically on either side of the window 2.
* * * * *