Machine for the plasma treatment of containers, comprising offset depressurization/pressurization circuits

Machine (1) for the plasma treatment of containers (3), which comprises: a chamber (5) suitable for receiving a container (3) to be treated, a cover (8) defining a nozzle (9) in the extension of the chamber (5); a duct (14) for depressurization the container (3), which duct opens into the nozzle (9) and connects the latter to a vacuum source (15); a first valve (19) having a closed position, in which it closes off the depressurization duct (14), and an open position, in which it brings the nozzle (9) and the vacuum source (15) into communication; a duct (27) for pressurizing the container (3), separate from the depressurization duct (14), this pressurization duct (27) emerging in the nozzle (9) beyond the depressurization duct (14) and connecting the nozzle (9) to a pressure source (28); and a second valve (29) having a closed position, in which it closes off the pressurization duct (27), and an open position, in which it brings the nozzle (9) and the pressure source (28) into communication.

The invention relates to the treatment of containers, consisting of coating their inner wall with a layer of a barrier effect material.

The depositing of barrier effect material by plasma enhanced chemical vapor deposition (PECVD) is known. Customarily, a machine equipped with a plurality of treatment units is used, each of which is comprised of at least one electromagnetic wave generator, a chamber connected to the generator and made of a conductive material (generally metal), as well as an enclosure provided in the chamber and made of a material (generally quartz) that is transparent to the electromagnetic waves produced by the generator.

After insertion of the container (generally made of a thermoplastic polymer material such as PET) into the enclosure, a depressurization is performed to establish in the container a high vacuum (several μbars, 1 μbar being equal to 10−6bar) necessary to establish the plasma, and in the enclosure outside the container a medium vacuum (on the order of 30 mbar to 100 mbar) to prevent the container from contracting from the effect of the difference in pressure on either side of its wall.

A precursor gas (such as acetylene, C2H2) is then introduced into the container, said precursor being activated by electromagnetic bombardment (this generally involves low power UHF microwaves at 2.45 GHz) in order to cause it to go through the cold plasma state and thus generate species including hydrogenated carbon (including CH, CH2, CH3), which is deposited in a thin layer (whose thickness is customarily between 50 and 200 nm, depending on the case, 1 nm being equal to 10−9m) on the inner wall of the container.

The plasma is generated for a predetermined length of time (on the order of a few seconds) during which the depressurization of the container is continued in order to draw out the undeposited species via an evacuation duct. The precursor gas feed, electromagnetic bombardment and depressurization are then stopped;

the container, then the enclosure, are pressurized; finally, the container is evacuated.

Uncontrolled pressurization (for example simply opening the enclosure to open air) could lead to a momentary imbalance between the internal and external pressures of the container, causing a contraction of said container and its subsequent rejection. This is the reason it is essential to control the pressurization of the enclosure and of the container, prior to the evacuation thereof. One widely used method consists of equipping the evacuation duct of the machine with a three-way valve connecting the container (or enclosure) either to a vacuum source or to the open air (i.e. to atmospheric pressure). An illustration of this principle can be found in U.S. Pat. No. 5,849,366 (The Coca-Cola Company).

Although this method has the dual advantage of simplicity and compactness, it has at least two flaws. Firstly, the pressurization causes the reinjection into the container of particles which, during the treatment, are deposited in the evacuation duct. These particles form a deposit in the container, which then must be cleaned out before proceeding with the filling thereof. Secondly, a carbonaceous deposit is formed even in the electrically operated valve, including in the open air channel. This flaw can, over time, affect the seal of this channel and lead to the appearance of harmful leaks upon depressurization of the container. The electrically operated valve must therefore be cleaned (or replaced) frequently, with the consequent shutdown of the machine and restriction of productivity.

The invention seeks in particular to correct these flaws by proposing a machine that can limit the pollution of the containers at the end of treatment, while guaranteeing good quality depressurization during said treatment.

To that end, the invention proposes a machine for treating containers by plasma, which comprises:an enclosure suitable for receiving a container to be treated,a cover defining a nozzle in the extension of the enclosure;a duct for the depressurization of the container, which opens into the nozzle and connects said nozzle to a vacuum source;a first valve having a closed position in which it closes off the depressurization duct, and an open position in which it brings the nozzle and the vacuum source into communication;a pressurization duct distinct from the depressurization duct, which pressurization duct opens into the nozzle beyond the depressurization duct and connects the nozzle to a pressure source; anda second valve having a closed position in which it closes off the pressurization duct, and an open position in which it places the nozzle in communication with the pressure source.

In this way, the pressurization duct is protected from particles produced by the plasma, which decreases the pollution created in the container by the pressurization at the end of the treatment, and ensures a more durable seal of the second valve, resulting in better quality vacuum in the container during treatment.

According to one embodiment, the nozzle has a central portion into which the depressurization duct opens, for example by means of an annular chamber communicating with the nozzle by an openwork partition. Said central portion is extended by a terminal portion into which the pressurization duct opens, for example by means of an annular chamber communicating with the central portion by one or more holes.

According to one embodiment, the machine can further comprise a duct for the depressurization of the enclosure, independent of the depressurization duct of the container and which connects the enclosure to a vacuum source, and a duct for pressurizing the enclosure, independent of the pressurization duct of the container and which connects the enclosure to a pressure source. The depressurization duct and the pressurization duct of the enclosure open into a common channel, for example, which opens into the enclosure.

Represented inFIG. 1is a machine1comprising two paired treatment units2for the plasma deposition of a barrier layer on the inner wall of containers3previously produced by blowing or stretch-blowing preforms of plastic material such as PET. The treatment units2are mounted at the periphery of a rotating carrousel (not shown) that can be disposed directly at the output of a container blowing machine.

Each treatment unit2comprises a chamber4made of a conductive material such as steel or preferably aluminum or aluminum alloy. Disposed in the chamber4is an enclosure5made of a material transparent to electromagnetic waves, such as quartz. The machine1also comprises a low-power generator6of electromagnetic microwaves at a frequency of 2.45 GHz, connected by waveguides7to each pair of chambers4of the treatment units2.

Each chamber4is topped by a cover8which, in the extension of the enclosure5at an upper end thereof, defines a nozzle9through which an injector10passes for the introduction of a precursor gas such as acetylene into the container.

A rod11, provided at a lower end with a device12for clamping the containers3by the neck, passes through the cover8. At a lower end, the enclosure5is sealed closed by a cap13. The cap13and the rod11are jointly and slidably mounted between an upper position, called closed (FIG. 1), wherein the cap closes the enclosure and the clamp presses the container against the cover, the mouth thereof being at least partially received into the nozzle, and a lower position, called open, wherein the cap13opens the enclosure5and the clamp12is located below the lower end of the enclosure5, in order to allow a treated container3to be evacuated and the next container to be loaded.

Each treatment unit2further comprises a duct14for the depressurization of the container3, which duct connects the nozzle9to a vacuum source15by means of channels16formed partly inside the treatment unit2and partly outside said unit. The vacuum source15, in practice composed of a pump unit that is common to all of the treatment units2, can be disposed outside the machine1.

The duct14for depressurization of the container3opens into the nozzle9. More specifically, the duct14opens into an intermediate chamber17, formed in the thickness of the cover8and which communicates with the nozzle9by an openwork partition with holes drilled therein.

The treatment unit2comprises a first electrically operated valve19, inserted between the nozzle9and the vacuum source15in order to allow or prevent communication between them, depending on the stage of progress of the treatment. Said electrically operated valve19comprises a valve20which extends through the intermediate chamber17and is mounted movably between a closed position in which it is applied against a valve seat21formed at the mouth of the depressurization duct14which it thus closes, preventing communication between the nozzle9and the vacuum source15, and an open position (FIG. 4) in which, moved away from the seat21, it places the nozzle9and the vacuum source15in communication.

The nozzle9has a central portion22, formed by a bore that extends from the junction of the nozzle9with the enclosure5(i.e., when a container3is received therein, from the mouth23of the container3) to the upper limit of the openwork partition18. Said central portion22constitutes a post-discharge zone flooded by the plasma, which plasma, however, is confined in the nozzle9by the presence of the partition18which, by a judicious choice of thickness and diameter of holes, forms a barrier to the electromagnetic waves which preserves the intermediate chamber17from the plasma.

The nozzle9, in the extension of the central portion22, that is, beyond the depressurization duct14, has a terminal portion24which comprises an annular chamber25connected to the bore of the central portion22by one or more oblique holes26forming zigzags (FIG. 3).

The treatment unit2further comprises a duct27for pressurization of the container3, distinct from the depressurization duct14. The pressurization duct27connects the nozzle9to a pressure source28which can be open air or a source of gas (such as air or another neutral gas) at a pressure equal to (or nearly equal to) the atmospheric pressure. Said pressurization duct27opens into the terminal portion24of the nozzle9, that is, beyond the pressurization duct14. More specifically, the pressurization duct27opens into the annular chamber25.

The treatment unit2comprises a second electrically operated valve29, inserted between the nozzle9and the pressure source28in order to allow or prevent communication between them, depending on the stage of progress of the treatment. Said electrically operated valve29comprises a valve30mounted movably between a closed position in which it is pressed against a valve seat31formed at the mouth of the pressurization duct27which it thus blocks, preventing communication between the nozzle9and the pressure source28, and an open position (visible inFIG. 5) where, moved away from the seat31, it places the nozzle9and the pressure source28in communication.

Thanks to this arrangement, during treatment of the container3the plasma, drawn through the partition18to the intermediate chamber17due to the vacuum caused by opening the electrically operated valve19, does not reach the terminal portion24of the nozzle9. Therefore, little or no carbonaceous species are deposited, not only in this terminal portion24, but also on the electrically operated valve29and the seat31. This results in a two-fold advantage. On the one hand, during the pressurization of the container3which follows the deactivation of the plasma by the cutoff of the electromagnetic microwaves, the air that surges through the pressurization duct27into the container3via the nozzle9carries few particles, which minimizes or eliminates the pollution of the container3at the end of treatment. On the other hand, the seal achieved by the closing of the second electrically operated valve29is preserved, to the benefit of the quality of the vacuum produced in the container3by the depressurization (during which the electrically operated valve29is kept closed).

Moreover, it is provided that the pressurization as well as the depressurization, inside both the container3and the enclosure5(outside the container3), are performed separately.

To that end, the machine1comprises, for each treatment unit2, a duct32for the depressurization of the enclosure5, separate from the duct14for the depressurization of the container3, and a duct33for the pressurization of the enclosure5, separate from the duct for the pressurization of the container3.

The depressurization duct32connects the enclosure5, outside the container3, to a vacuum source15, which can be the same as the one to which the container3is connected via the duct14.

The treatment unit2comprises a third electrically operated valve34inserted between the enclosure5and the vacuum source15to allow or prevent communication between them. Said electrically operated valve34comprises a valve35mounted movably between a closed position in which it is applied against a valve seat36formed at the mouth of the depressurization duct32that it closes off, preventing communication between the enclosure5and the vacuum source15, and an open position (visible inFIG. 6) in which, moved away from the seat36, it places the enclosure5in communication with the vacuum source15.

The pressurization duct33connects the enclosure5, outside the container3, to a pressure source28which can be open air or a source of gas (such as air or other neutral gas) at a pressure equal (or nearly equal) to the atmospheric pressure. Said pressure source28can be the same as the one to which the container3is connected via the duct27.

The treatment unit2comprises a fourth electrically operated valve37inserted between the enclosure5and the pressure source28to allow or prevent communication between them. Said electrically operated valve37comprises a valve38mounted movably between a closed position in which it is applied against a valve seat39formed at the mouth of the pressurization duct33which it thus closes off, preventing communication between the enclosure5and the pressure source28, and an open position (visible inFIG. 6) in which, moved away from the seat39, it places the enclosure5in communication with the pressure source28.

As shown inFIGS. 1 and 6, the depressurization duct32and the pressurization duct33of the enclosure5both open into a common channel40which opens into the enclosure5, outside the container3.

The injector10is connected to a source41of precursor gas (such as acetylene) by a duct42formed partly in the cover8and which can be opened or closed by a fifth electrically operated valve43.

According to an embodiment illustrated inFIG. 1, the depressurization duct32and the pressurization duct33of the enclosure5, as well as the third electrically operated valve34and the fourth electrically operated valve37, are common to the same pair of treatment units2, resulting in a compactness of the machine1.

The electrically operated valves19,29,34,37,43are controlled by a control unit (not shown) which controls the automated functions of the machine during the treatment, the principal steps of which are now described with reference toFIG. 7, in which:the line entitled Vide in [Int. Vac.] designates the condition, open (O) or closed (F) of the first electrically operated valve19;the line entitled Vide ext. [Ext. Vac.] designates the condition, open (O) or closed (F) of the third electrically operated valve34;the line entitled “Patmint.” designates the condition, open (O) or closed (F) of the second electrically operated valve29;the line entitled “Patmext.” designates the condition, open (O) or closed (F) of the fourth electrically operated valve37;the line entitled “C2H2” designates the condition, open (O) or closed (F) of the fifth electrically operated valve43, allowing the injection of acetylene into the container3; andthe line entitled “μondes” [μwaves] designates the condition, active (O) or inactive (F) of the microwave generator6.

The cap13and the rod11are initially in the lower position to allow a container3to be loaded. The enclosure5with no container3therein is thus open to the air.

A container3is loaded, its neck held in the clamping device12. The rod11rises, together with the cap13, to the upper position where the container3is held rigidly sealed between the clamping device12and the cap8. The purpose of said seal is to prevent any communication between the nozzle9(and thus the interior of the container3) and the enclosure5(i.e., the exterior of the container3) in order to prevent the carbonaceous pollution of the enclosure5, which would be detrimental to the good transmission by the enclosure of the electromagnetic microwaves.

At the moment the rod11and the cap13reach their upper position, the valves30and38of the second electrically operated valve29and fourth electrically operated valve37are in the closed position (see lines Patmint. and Patmext.). That moment serves as the origin on the time axis (abscissa) of the timing chart ofFIG. 7.

At that moment (or after a time-out, if any), the valves20,35of the first electrically operated valve19and third electrically operated valve34, controlled by the control unit, change to the open position to provide the depressurization of the interior of the container3and of the enclosure5(outside of the container3) by placing them in communication with the vacuum source15(see lines Vide in [Int. Vac.] and Vide ext. [Ext. Vac.]). When the pressure in the enclosure5(outside the container3) has reached the desired value (several dozen mbar), the valve35of the third electrically operated valve34changes, under the control of the control unit, to the closed position so that the pressure in the enclosure5is maintained at that value (see the line Vide ext. [Ext. Vac.]), while the valve20of the first electrically operated valve19is held in the open position to continue the depressurization of the interior of the container3.

At that moment, the fifth electrically operated valve43is opened by the control unit in order to introduce the precursor gas into the container3via the injector10(see line C2H2).

After a time-out to allow the precursor gas to occupy the entire volume of the container3, the microwave generator6is activated, which causes the genesis of a cold plasma in the interior of the container, the ionized species of which plasma are deposited in a thin film on the inner wall of the container3, thus forming a barrier layer thereon.

Throughout the duration of the plasma, the valve20of the first electrically operated valve19is kept open so as to continue the depressurization of the container3and thus evacuate the species generated by the plasma that would not be deposited on the wall of the container3. As we have already mentioned, although the focus of the plasma is located in the container3, the plasma is propagated in the nozzle9, and more specifically in the central portion22(post-discharge zone) perpendicular to the partition18through which the undeposited species are drawn, however without the plasma reaching the terminal portion24of the nozzle9.

After a predetermined period of time (on the order of a few seconds), the control unit simultaneously controls:the deactivation of the electromagnetic microwave generator6, causing the clearing of the plasma;the closing of the fifth electrically operated valve43, causing the precursor gas feed to stop;the change of the valve20of the first electrically operated valve19to the closed position, causing the depressurization of the container3to stop; andthe change of the valve30of the second electrically operated valve29to the open position, causing the pressurization of the container3.

After a predetermined time-out (a fraction of a second), the control unit controls the change of the valve38of the fourth electrically operated valve37to the open position, causing the pressurization of the enclosure5outside the container3.

The container3thus treated can then be evacuated, the cycle being repeated for the treatment of the next container.