Abstract:
A container-treatment method, of the type in which the container ( 12 ) is disposed inside a chamber ( 16 ) which defines a cavity ( 18 ) outside the container ( 12 ) and which is connected to a Vacuum pumping circuit ( 50 ), the interior of the container ( 12 ) being connected to the pumping circuit ( 50 ). The method includes a preliminary pumping step (E 1 ) which is followed by a treatment step (E 2 ). The preliminary step (E 1 ) includes the following successive phases, namely: an external pumping phase (P 1 ) which produces a drop in the pressure inside the cavity ( 18 ) only; and an internal pumping phase (P 2 ) which produces a drop in the pressure inside the container ( 12 ) only. A machine used to implement the method is also disclosed.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a method and a machine for treating containers made of plastic such as bottles made of polyethylene terephthalate (PET). 
     The present invention relates more particularly to a method for treating at least one container aimed at depositing an internal coating forming a barrier by means of a microwave plasma, in particular with a view to enabling oxido-sensitive liquids to be packaged in the container, of the type in which the container is disposed inside a hermetically sealed treatment chamber which delimits a cavity outside the container and which is connected to a vacuum pumping circuit by an external vacuum line, the interior of the container being connected to the pumping circuit by an internal vacuum line, of the type comprising a preliminary step during which the pumping circuit produces a pressure reduction inside the cavity to a set value called the final external value, and a pressure reduction in the container to a set value called the final internal value, the preliminary step being followed by a treatment step during which the final values are maintained inside the cavity and inside the container so as to enable the internal coating to be deposited inside the container. 
     During the treatment step, a precursor fluid (for example based on acetylene in the case of the production of a carbon-containing coating, or an organosilicon-containing compound in the case of a silica-based deposit) is injected into the container and subjected to the action of microwaves so that it passes to the plasma state and produces a barrier deposit on the internal walls of the container. 
     In order to produce this deposit, it is necessary to create the vacuum inside the container and inside the cavity, and to maintain this vacuum during the entire treatment step. 
     Generally, the desired pressure inside the container is approximately 0.1 mbar and the desired pressure inside the cavity is approximately 50 mbar. 
     It is known to carry out the preliminary step by simultaneously pumping from the cavity and from the container until the pressure inside the cavity reaches the final external value (approximately 50 mbar). 
     A closing device then hermetically seals the cavity so as to enable the pressure to fall inside the container to the final internal value which is lower than the final external value. 
     Simultaneous pumping from the cavity and from the container can present considerable problems since it is difficult to control the rate at which the pressure falls in each of the two elements. 
     Indeed, according in particular to the cross sections of the passage for air drawn out of the container and out of the cavity, and the shape of the container, the vacuum forms very rapidly in the container and more slowly in the cavity, so that during a particular length of time, the pressure difference between the interior of the container and the cavity reaches a value greater than the capacity of the container to resist mechanical crushing. 
     Generally, a PET container does not withstand more than a pressure reduction of 70 to 80 mbar. 
     The difference in pressure between the two elements therefore causes the container to collapse on itself which causes the container to be rejected and possibly causes the treatment machine to stop. 
     In order to avoid these problems, it is possible to increase the mechanical strength of the container, for example by increasing the thickness of the walls. 
     This solution is not satisfactory since it leads to an increase in the weight and cost of the container. 
     The mechanical strength of the container may also be increased by choosing a suitable shape. 
     This solution is not satisfactory either since it constitutes a technical constraint which prevents the external shape of the container from being freely chosen. 
     SUMMARY OF THE INVENTION 
     The invention aims in particular at remedying these disadvantages in a simple and economic manner. 
     With this aim, the invention provides a treatment method of the type previously described, characterized in that the preliminary step comprises successively:
         an external pumping phase, during which the internal vacuum line is closed and the external vacuum line is open, the pumping circuit producing a pressure reduction only inside the cavity, to a set value which is greater than or equal to the final external value,   and, an internal pumping phase, during which the external vacuum line is closed and the internal vacuum line is open, the pumping circuit producing a pressure reduction only inside the container, to the final internal value.       

     According to another feature of the invention, during the external pumping phase, the pumping circuit reduces the pressure inside the cavity to an intermediate value which is greater than the final external value, and an intermediate pumping phase is provided between the external pumping phase and the internal pumping phase, during which the external vacuum line and the internal vacuum line are opened simultaneously so that the pumping circuit reduces the pressure simultaneously inside the cavity and inside the container, until the pressure inside the cavity reaches the final external value. 
     The invention also provides a machine for treating bottles for implementing the method according to one of the preceding features, comprising at least one treatment station for at least one container, each treatment station comprising:
         a treatment chamber which is provided so as to contain at least one container and which delimits, around the container, a cavity connected in a leakproof manner to an external vacuum line,   and, an internal vacuum line connected in a leakproof manner to the interior of the container,
 
of the type in which the external vacuum line and the internal vacuum line are connected to a common vacuum pumping circuit, the internal vacuum line communicating with the pumping circuit via a first controlled closing device and the external vacuum line communicating with the pumping circuit via a second controlled closing device,
 
characterized in that the external vacuum line is directly connected to the pumping circuit without passing through the internal vacuum line, and in that the first closing device is controlled so as to enable the cavity and the container to be pumped independently of each other.
       

     According to other features of the machine according to the invention:
         at least one closing device consists of a valve controlled by a cam system;   at least one closing device consists of a solenoid valve.       

    
    
     
       BREIF DESCRIPTION OF THE DRAWING FIGURES 
       Other features and advantages of the invention will become apparent from reading the following detailed description, for an understanding of which reference will be made to the appended drawings in which: 
         FIG. 1  is an axial sectional view which diagrammatically represents a treatment station of a machine produced according to the teachings of the invention and which illustrates an external pumping phase; 
         FIG. 2  is a similar view to that of  FIG. 1  which illustrates an internal pumping phase. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIGS. 1 and 2  diagrammatically represent a machine  10  for treating containers  12 , consisting here of bottles  12 , for implementing the method according to the invention. 
     The machine  10  can be produced in the form of a carousel comprising a series of identical treatment stations  14  which are distributed circumferentially around a main rotational axis. 
       FIGS. 1 and 2  partially represent a treatment station  14  provided for a bottle  12 . 
     The treatment station  14  comprises a treatment chamber  16  which is designed to contain the bottle  12  and which delimits, around the bottle  12 , a cavity  18  connected in a leakproof manner to an external vacuum line  20 . The chamber  16  is made of a material transparent to microwaves, typically quartz. 
     The bottle  12  is here arranged vertically in the chamber  16  so that its neck  22  extends upward through a corresponding upper opening  24  of the chamber  16 . 
     For the remainder of this description, a vertical axial direction is defined, in a nonlimiting manner, following the vertical axis of the bottle, and a transverse direction in relation to this axial direction. 
     Advantageously, the external vacuum line  20  emerges inside the cavity  18  through a lower opening  26  which is made in the lower transverse wall  27  of the chamber  16 . 
     The chamber  16  is itself contained within a casing  28  which is associated with a microwave generator  30 . 
     The upper axial end of the chamber  16  is in leakproof contact with the upper transverse wall  31  of the casing  28 , so that the upper opening  24  of the chamber  16  is arranged facing an associated opening  33  provided in said upper transverse wall  31 . 
     The treatment station  14  has a cover  32  which is designed to close the upper opening  24  of the chamber  16  in a hermetically sealed manner and which includes an internal vacuum line  34 , or pumping chamber, connected in a leakproof manner to the interior of the bottle  12 . 
     According to the embodiment shown here, the lower transverse wall  36  of the cover  32  is provided with a tubular-shaped pipe  38  which extends axially downward and which has a lower transverse annular surface  40  resting in a leakproof axial manner against the upper transverse wall  31  of the casing  28  so as to close the opening  33  of the casing  28  and the upper opening  24  of the chamber  16 . 
     The pipe  38  provides a leakproof connection between the internal vacuum line  34  and the interior of the bottle  12  through a passage  35  provided in the lower transverse wall  36  of the cover  32 . 
     The pipe  38  is provided with a holding device  42  which is designed for grasping the bottle  12  externally by its neck  22 . 
     An injector  44  for precursor fluid is arranged on the upper transverse wall  46  of the cover  32 . The injector  44  has an injection tube  48  which extends axially downward through the cover  32  and through the neck  22  of the bottle  12 . 
     The external vacuum line  20  and the internal vacuum line  34  are connected to a common vacuum pumping circuit  50 . 
     The pumping circuit  50  is connected to a vacuum pump (not shown). 
     According to the teachings of the invention, the external vacuum line  20  is directly connected to the pumping circuit  50  via a closing device  52 , controlled for example by a solenoid valve. 
     The external vacuum line  20  is not connected to the internal vacuum line  34  of the cover  32 . 
     The internal vacuum line  34  communicates with the pumping circuit  50  via a connecting orifice  54  which is made here in the lower transverse wall  36  of the cover  32 . 
     Preferably, as illustrated in the figures, the connecting orifice  54  is provided with a controlled closing device  56  so as to enable the cavity  18  and the bottle  12  to be pumped independently of each other. 
     The controlled closing device  56  fitted to the connecting orifice  54  can be controlled by any suitable actuator  58  (a cam actuator or, preferably, an electromagnetic actuator, so that in this case the controlled closing device  56  consists of a solenoid valve). 
     A method for treating a container, consisting of a bottle, will now be described, according to the teachings of the invention and implemented by means of the machine  10  which has just been described. 
     The treatment method aims at depositing a coating called a barrier layer on the internal walls of the bottle  12  by means of a microwave plasma, in particular with a view to enabling oxido-sensitive liquids to be packaged in the bottle  12 . 
     The treatment method comprises a preliminary step E 1  during which the pumping circuit  50  produces a pressure reduction inside the cavity  18  to a set value called the final external value pFext and a pressure reduction inside the bottle  12  to a set value called the final internal value pFint which is lower than the final external value pFext. 
     The preliminary step E 1  is followed by a treatment step E 2  during which the final values pFext, pFint are maintained inside the cavity  18  and inside the bottle  12  so as to enable the internal coating to be deposited in the bottle  12 . 
     According to the teachings of the invention, the preliminary step E 1  comprises successively an external pumping phase P 1 , which is illustrated in  FIG. 1 , and an internal pumping phase P 2 , which is illustrated in  FIG. 2 . 
     During the external pumping phase P 1 , the closing device  56  is controlled in a closed position, as shown in  FIG. 1 , which closes the communication between the internal vacuum line  34  and the pumping circuit  50 , and the closing device  52  is controlled in an open position which causes the external vacuum line  20  to communicate with the pumping circuit  50 . 
     The pumping circuit  50  then produces a pressure reduction only in the cavity  18 , to a final external value pFext capable of enabling the bottle  12  to be treated. 
     During the external pumping phase P 1 , the pressure inside the bottle  12  and inside the internal vacuum line  34  remains substantially constant. 
     During the internal pumping phase P 2 , the closing device  52  is controlled in a closed position, which closes the communication between the external vacuum line  20  and the pumping circuit  50 , and the closing device  56  is controlled in an open position, as shown in  FIG. 2 , which causes the internal vacuum line  34  to communicate with the pumping circuit  50 . 
     The pumping circuit  50  then produces a pressure reduction only inside the bottle  12 , to a final internal value pFint, capable of enabling the plasma to be formed in order to carry out the treatment. 
     The treatment step E 2  can then be put into operation. 
     During the treatment step, the pumping circuit  50  can continue to pump inside the bottle  12  so as to maintain the pressure at its final internal value pFint. 
     The final external value pFext is maintained in the cavity  18  by adequately sealing the chamber  16  and the external vacuum line  20 . 
     It will be noted that the preliminary step E 1  of the method according to the invention does not cause any time to be lost, compared with the operation of the method according to the prior art, since the final values pFext, pFint are obtained more rapidly by independent pumping from the cavity  18  and then from the bottle  12 , rather than pumping simultaneously from the two elements. 
     According to a variant of the method according to the invention, during the external pumping phase P 1 , the pumping circuit  50  reduces the pressure inside the cavity  18  to an intermediate value pMext which is greater than the final external value pFext. 
     An intermediate pumping phase Pm is then put into operation, between the external pumping phase P 1  and the internal pumping phase P 2 , during which the closing device  56  and the closing device  52  are open simultaneously, so that the external vacuum line  20  and the internal vacuum line  34  communicate simultaneously with the pumping circuit  50 . 
     The intermediate pumping phase Pm is put into operation until the pressure inside the cavity  18  reaches the final external value pFext. 
     The closing device  52  is then closed and the internal pumping phase P 2  is put into operation. 
     The invention is completely applicable to treatment machines which, instead of enabling a single container to be treated by the treatment station  14 , would enable several containers to be treated. 
     In addition, instead of being made partially in the cover  32 , and therefore in a movable structure, the internal vacuum line  34  could be in another part of the treatment station  14 .