Patent Application
20100000856
The present invention relates to a method and a device for controlling a high-voltage power supply generator for a magnetron for the cold-plasma deposition of a barrier layer. It also relates to a machine for cold-plasma deposition of a barrier layer using such a device.
In the prior art, methods have already been described which, after the injection of precursor gases, or even gas mixtures, for example based on carbon and/or silicon, into a hollow body made from plastic such as PET, are suitable for producing a cold plasma leading to the formation of barrier layers. These layers are particularly suitable when the hollow bodies are containers: this is because they allow the contents, subsequently filled in the container, to be protected from gas exchanges with the exterior, particularly with oxygen in the air. Such a protection is particularly advantageous, for example, but not exclusively, when the product filled in the container is a food.
In the prior art, such methods are implemented using machines for the cold-plasma deposition of a barrier layer comprising at least one treatment station with a cavity and a magnetron generating microwaves. At least one hollow body to be treated is introduced into the cavity and the microwave power, which is applied at a convenient location in the inner volume of the hollow body containing precursor gas previously injected, generates a cold plasma of which the active species are projected against the wall of the hollow body. The whole of these active species forms the barrier deposit against gas exchanges between the interior and the exterior of the hollow body.
However, the prior art devices for generating the electric power supply of the magnetron, which convert the electric power they receive to a microwave power which they radiate, do not have optimized performance for such a deposition of an internal barrier layer.
To obtain high production rates, it is known that the barrier layer deposition machines comprise a plurality of workstations (up to 48 on hitherto known machines) each comprising at least one magnetron or one radiant antenna connected to a magnetron. This has the result that the failure of a single one of these magnetrons causes production losses. Furthermore, a poor definition of the electric power supply of the magnetron (power waveform) limits the performance of the process and the service life of this magnetron.
The present invention provides a remedy to these drawbacks of the prior art, in that it relates to a method for controlling a high-voltage power supply generator for a magnetron for producing a cold plasma inside a hollow body in order that a barrier layer becomes deposited within the hollow body.
According to a first of its aspects, the present invention relates to a method for controlling a high-voltage power supply generator for a magnetron for producing a cold plasma inside a hollow body in order to carry out the deposition of a barrier layer within said hollow body, characterized in that it consists in selecting a generator operating mode from a plurality of operating modes, a modification of the operating mode of the generator varying at least one coefficient defining a maximum power Pmax of the waveform of the supply power of the magnetron according to an average power setpoint Pavg of the magnetron, the magnetron supply waveform being repeated recurrently with a cyclic conduction ratio Th depending on the average power setpoint Pavg and/or the maximum power Pmax.
Advantageously, the maximum power Pmax of the waveform is predetermined according to the power setpoint Pavg.
According to a first embodiment of an operating mode of the method according to the invention, said relation between the average power Pavg and the maximum power Pmax has the polynomial form
P
max
=a*(Pavg)n+b*(Pavg)n-1+c*(Pavg)n-2+ . . . +k*(Pavg)n-p,
where n and p are whole numbers, n being higher than or equal to p, and (a, b, c, . . . k) being variable coefficients.
Advantageously, said polynomial equation has a parabolic form Pmax=a*(Pavg)2+b*Pavg+c where a, b, c are variable coefficients.
Preferably, the cyclic conduction ratio Th, in percent, is determined by the relation
Th=100*Pavg*π/(2*Pmax).
According to a second embodiment of an operating mode of the method according to the invention, the cyclic conduction ratio Th, in percent, is dependent on the average power setpoint Pavg via the polynomial equation having the formula
Th=a1*(Pavg)n+b1*(Pavg)n-1+c1*(Pavg)n-2+ . . . +k1*(Pavg)n-p
where n and p are whole numbers, n being higher than or equal to p, and (a1, b1, c1, . . . k1) being variable coefficients.
Advantageously, said polynomial relation has a parabolic form Th=a1(Pavg)2+b1*Pavg+c1, where a1, b1, c1 are variable coefficients.
Preferably, the maximum power Pmax is determined by the relation Pmax=π*Pavg/(2*Th).
Advantageously, in one operating mode, none of the coefficients is zero.
Alternatively, in another operating mode, at least two coefficients are zero.
More precisely, in one operating mode, the maximum power Pmax is fixed constant.
Similarly, the cyclic ratio Th is linearly dependent on the average power Pavg.
Advantageously, the maximum power is determined and adapted for varying on the basis of a safe area bounded by a maximum permissible value of the maximum power Pmax,max for the magnetron and a lower value of the maximum power Pmax,min determined by a maximum cyclic conduction ratio Thmax given by the design of the magnetron and of the power supply thereof.
Advantageously, in one further operating mode, the maximum power Pmax is linearly dependent on the value of the average power setpoint Pavg.
In still another operating mode, the cyclic conduction ratio Th is fixed.
Still in the same other operating mode, the cyclic conduction ratio Th of the waveform is determined and selectable on the basis of a safe area bounded by a value of the maximum permissible cyclic conduction ratio Thmax and a lower value of the minimum cyclic conduction ratio Thmin determined in relation with the upper limit of the maximum permissible power Pmax,max which depends on the characteristics of the magnetron and of the power supply thereof.
Advantageously, said coefficients are determined by tests of treatment of a batch of hollow bodies from which a relation is derived between the average power setpoint Pavg, the maximum power Pmax and the cyclic conduction ratio Th.
Advantageously, the coefficient a is between (−0.0020) and 0.0020, the coefficient b is between 0 and 4, and the coefficient c is between 0 and 3000.
According to a second of its aspects, the present invention relates to a device for controlling a high-voltage power supply generator for magnetron for the cold-plasma deposition of a barrier layer of the invention, of the type comprising:
a circuit for controlling a high-voltage power supply generator;
a circuit for controlling the control electrodes of a power switch bridge in relation with a power waveform setpoint, said control device using the method as described above and comprising:
means for storing parameters of maximum power, of conduction in relation with a predefined operating mode,
means for selecting an average power setpoint Pavg,
means for determining an operating frequency,
means for selecting an operating mode for the generator, and
means for determining all the instantaneous setpoint characteristics defining the power wave for a work target expressed in terms of performance of the deposit created on the hollow body and the respect of integrity thereof while controlling the temperature rise thereof during the deposition.
According to a third of its aspects, the present invention relates to a machine for depositing a barrier layer on the inside wall of a plastic hollow body, such as a bottle, using a cold plasma excited by a magnetron, supplied by a high-voltage generator, controlled by a control device as mentioned above.
Other features and advantageous of the present invention will be more clearly understood from the description of an example exclusively illustrative and nonlimiting of the scope of the invention, and in conjunction with the appended figures in which:
a and 4b show two functions respectively illustrating the variation of the maximum power Pmax in relation with the average power Pavg and the variation of the cyclic conduction ratio Th in relation with the average power Pavg, for determining the electric power supply of the magnetron according to two alternatives of a first operating mode of the electric power supply generator according to the invention (MODE 1);
in a first part 1a: a member for treating and controlling a device for controlling a high-voltage power supply generator for magnetron;
in a third part 1c: the high-voltage part of the power supply and of the current and voltage measurements of the magnetron 16.
The control device of the invention comprises a treatment member 1a shown in part 1a constructed around a microcontroller 10 which receives at least two measurement signals and one setpoint signal, that is:
a current Is measurement signal, the image of the current supplying the anode of the magnetron 16, delivered by the part 1c, the magnetron 16, and more precisely the filament thereof, being powered by a transformer 15;
a voltage Us measurement signal, the image of the power supply voltage between the anode of the magnetron 16 between the power supply from the circuit 1c and mass;
a setpoint signal Pavg (average power setpoint) supplied by a member 11 for determining the power setpoint.
The control device of the invention is implemented in the form of a program recorded in the memory of the microcontroller 10, one embodiment of the control method according to the invention adapted to the high-voltage power supply generator for magnetron 16 being described in greater detail below. The recorded program, when run in particular by the “DSP” circuit of the microcontroller 10 of the control device comprising the parts 1a to 1c, periodically detects the average setpoint Pavg supplied by the member 11 as well as the values of the current Is and voltage Us measurements and determines four control signals, respectively IG1 to IG4 sent to two circuits 13a and 13b for controlling power switches Q1 to Q4 which modulate the energy supplied by the power supply 19 using the PWM (Pulse Width Modulation) technology. The power transfer is provided by the circuit 12 which consists of a resonance filter. The modulation, controlled by the circuits 13a and 13b, is carried out by power switches Q1 to Q4 capable of switching high power levels in high frequency. The primary part of the high-voltage transformer is incorporated in the resonant circuit 12.
It is already known in the prior art to provide devices for depositing a barrier layer on plastic hollow bodies using a cold plasma excited and maintained by means of a magnetron producing microwave radiation when a suitable precursor gas (single gas or gas mixture) has been introduced into the plastic hollow body. The magnetron must be connected to a high-voltage generator. In order to convert the A.C. voltage produced in the part 1b (that is the resonance converter part) to an A.C. high voltage, it is known to use a high-voltage step-up transformer 17 of which the primary circuit integrated in the filter 12 is connected in the current branch located between the four power switches Q1 to Q4, and of which the secondary is connected to a high-voltage rectifier bridge 18, consisting for example of four diodes mounted in a manner known (such as a Graetz bridge). Moreover, to carry out a filtering so as to adjust the maximum values of the high-voltage wave delivered at the output of the rectifier bridge 18, it is known to use magnetic-core coils (not shown) for filtering the current at the terminals of the magnetron 16.
Downstream of the filtering, the magnetron 16 is connected via the “negative high voltage”−HT and “positive high voltage”+HT connections, used to connect the “high voltage” mass electrodes and the “high voltage” filament. A third filament heating connection is also provided, and the “negative high voltage”−HT power supply as well as the filament heating voltage are supplied by a power supply transformer 15 adapted to the magnetron 16. The “positive high voltage”+HT terminal is connected to the high voltage mass of the inventive device.
In a by-pass between the two “negative high voltage” and the “positive high voltage” terminals of the high-voltage power supply generator, a circuit for measuring the instantaneous voltage is provided which the “negative high voltage” potential Us, the image of the supply voltage between the anode of the magnetron and the mass thereof, with which the magnetron 16 is supplied to be measured and of which the instantaneous measurement allows to represent the radiant microwave energy that is applied in order to excite the molecular species in the gas and to maintain the cold plasma, generating the barrier layer.
Furthermore, the measurement of the current Is, the image of the current supplying the anode of the magnetron 16, delivered by the resonance converter part 1b, is carried out at the output of the high voltage rectifier bridge 18.
As a result, the precise control of the current delivered by the resonance converter part 1b as well as the voltage applied to the magnetron 16 thereby allows to produce a representation of the instantaneous power consumption of the magnetron 16. Thanks to a predefined relation of the conversion of electric power to microwave power provided by the magnetron 16, it is possible to control the state of the cold plasma generated in the introduced precursor gas.
In a prior step, during numerous tests, a determination—is carried out of the optimal characteristics of the power wave (form, frequency, peak value) to be applied to the magnetron 16 in order to produce a satisfactory barrier layer without excessively heating the plastic hollow body. In fact, it is indispensable to generate a barrier layer with precise characteristics while controlling the temperature rise of the plastic wall of the hollow body, so as to avoid deforming or altering the appearance thereof. It results in that it is thanks to the control of the characteristics defining the wave aas well as of the pressures under which the gas mixture is distributed into the hollow body that a proper barrier layer is thereby produced. To make the production of a high-voltage power supply wave of the magnetron readier and better controllable in order to obtain hollow bodies correctly coated with a homogeneous barrier layer, without said bodies being subjected to an excessively high temperature of the cold plasma, and in order for the deposit to have a layer with the desired barrier properties, related in particular to the homogeneity and the thickness thereof, the invention proposes a method for generating a power wave controlled according to a plurality of operating modes, whereby it is possible to readily change a mode for generating a power supply waveform of the magnetron in relation with the characteristics of the hollow body and of the injected gas, and to select an optimal operating mode of the generator in relation with several characteristics of a generic magnetron supply waveform.
In general, the cyclic conduction ratio Th is defined by the ratio Th=Tmo/T, where Tmo is the active time of the elementary wave, and T the recurrence period. The average of the power Pavg is then defined over the period T. It is obtained by calculating the average power from 0 to T
which in the case of a wave in the form of a sinusoid arch leads to:
The method according to the invention allows to select the waveform, the cyclic conduction ratio Th thereof, as well as the percentage of modification thereof (in other words the homothetic transformation thereof) from one recurrence to another so as to adapt to objectives of treatment by barrier layer deposition defined in terms of coloration of the hollow body treated, temperature of the hollow body during the application of the microwave plasma, and in terms of uniformity of the barrier layer, the uniformity being expressed in particular in terms of thickness of deposit.
In particular, the invention sets a predefined condition between the average power setpoint Pavg, the maximum power Pmax and the cyclic conduction or repetition ratio Th of the waveform. For example, in the case in which the waveform is fixed during a sufficiently long period in a sinusoid arch waveform, such a predefined condition can be expressed by an equation having the form: Pavg=(2*Pmax*Th)/π where “π” refers to the angular units.
In the exemplary embodiment in
So as to control the operation of the high-voltage power supply generator of the magnetron 16, an operating mode is determined in which an average power setpoint is assumed, which will be denoted in the following description by Pavg, it being understood that the control device of the invention, according to the selected operating mode, comprises means for determining:
the actual waveform, preferably as a sinusoid arch waveform,
the parameters determining the wave, like the cyclic conduction ratio Th of the microwaves with respect to the waveform recurrence period T, and the maximum power Pmax. The wave is defined by the shape thereof (preferably a positive sinusoid half-arch), the natural period thereof and the recurrence period thereof connected by the conduction ratio Th, and the maximum power Pmax.
In other words, the present invention proposes a method for controlling a high-voltage electric power supply generator for magnetron 16 for producing a cold plasma inside a hollow body in order to deposit a barrier layer inside said hollow body, characterized in that it consists in selecting a generator operating mode from a plurality of operating modes, the modification of the generator operating mode causing the variation of at least one coefficient defining a maximum power Pmax of the waveform of the supplied power of the magnetron 16 in relation with an average power setpoint Pavg of the magnetron 16, the waveform supplying the magnetron 16 being repeated with a recurrence having a period T.
a shows the variation in the value of the maximum power Pmax of the supply wave of the magnetron 16 as a function of the average power setpoint Pavg of the magnetron 16 (in other words, the power consumption of the magnetron 16).
During numerous tests, using magnetrons with a capacity lower than 1 kW and operating with a rated frequency of about 2.45 GHz and a sinusoidal waveform, it was determined that for a rated frequency, the maximum power Pmax is correctly represented by a section of parabola determined by an equation like:
P
max
=a*(Pavg)2+b*Pavg+C
where the constants a, b and c are determined from tests performed on a significant range of hollow bodies used in the barrier layer deposition machines of the invention.
More generally, it has been found that the equation between the average power Pavg and the maximum power Pmax has a polynomial form
P
max
=a*(Pavg)n+b*(Pavg)n-1+c*(Pavg)n-2+ . . . +k*(Pavg)n-p,
where n and p are whole numbers, n being higher than or equal to p, and (a, b, c, . . . , k) being variable coefficients, it being understood that the preferential form of the equation is a parabolic form.
a thus shows a section of a parabolic curve between two limit operating points of the generator according to a first operating mode between a point where the average power Pavg,min is a minimum and where the maximum power has a lower bound value Pmax,min and a point where the average power is a maximum Pavg,max and where the maximum power has an upper bound value Pmax,max.
It has already been shown that the cyclic conduction ratio could be given by the following equation, Th(%)=100*Pavg*π/(2*Pmax) for a sinusoidal waveform. In general, the cyclic conduction ratio may be given by a formula of the type Th=F(Pavg).
Thus, having the two characteristic curves Pmax=f(Pavg) and Th=F(Pavg), it suffices for the user to define the desired setpoint value Pavg. In a particular embodiment, the microcontroller also comprises means for determining the values Pmax and Th automatically, knowing the other indispensable parameters (frequencies, etc.), on the basis of a map storage incorporating the abovementioned two curves, varied according to said indispensable parameters. The characteristics of the sinusoidal arch wave to be used during the regulation of the microwaves (supply of the magnetron) are thereby accurately calculated.
These two characteristic curves f(Pavg) and F(Pavg) allow, in combination, to establish a first operating mode for obtaining the objectives described above for the hollow body and the barrier layer thereof deposited by cold plasma.
Alternatively, when the cyclic conduction ratio Th is not modeled by the equation having the formula Th(%)=100*(Pavg)*π/(2*Pmax) (that is when the waveform is not of a sinusoidal type), it is also possible to model the variation of the cyclic conduction ratio Th in relation with the average power Pavg.
To do this, during numerous tests, using magnetrons with a capacity lower than 1 kW and operating at a rated frequency of about 2.45 GHz, it was determined that the cyclic ratio Th could also be modeled by a section of parabola determined by an equation like Th=a1*Pavg2+b1*Pavg+c1 limited by the coordinate points (Pavg,min; Thmin) and (Pavg/max; Thmax) in which the constants a1, b1 and c1 are established from tests performed on a significant range of hollow bodies used in the barrier layer deposition machines of the invention.
More generally, it has been found that the cyclic conduction ratio Th, as a percentage, is dependent on the average power setpoint Pavg by the polynomial equation having the formula
Th=a1*(Pavg)n+b1*(Pavg)n-1+c1*(Pavg)n-2+ . . . +k1*(Pavg)n-p,
where n and p are whole numbers, n being higher than or equal to p, and (a1, b1, c1, . . . k1) being variable coefficients.
In the case in which the wave has a sinusoidal form, the maximum power Pmax is thus calculated from the equation having the following formula
P
max
=π*P
avg/2*Th).
In this way, knowing the two characteristic curves Pmax=g(Pavg) and Th=G(Pavg), it suffices for the user to define the desired setpoint Pavg so as to operate the generator according to the first operating mode of the invention.
Thus, in short, the first generator operating mode comprises two alternatives in the case of the use of a sinusoidal waveform, in which either the pair of formulas (Pmax=a*(Pavg)2+b*Pavg+c; Th(%)=100*Pavg*Pi/(*2Pmax)) are applied, or the pair of formulas (Th=a1*Pavg2+b1*Pavg+c1; Pmax=π*Pavg/(2*Th)) are applied. The choice of the pair of formulas to be applied depends on the control parameters of the device for plasma deposition of the barrier layer (for example, the precursor gas injection rate, internal volume, etc.).
The variations in maximum power Pmax are shown as a function of the average microwave power Pavg. The maximum power Pmax of the second operating mode is determined according to the desired characteristics of the containers after treatment. It is selected in the trapezoidal area bounded by the vertical lines corresponding to a minimum average power Pavg,min and to a maximum average power Pavg,max, by a horizontal line 33 corresponding to an upper bound value of the maximum power Pmax,max not to be exceeded by the magnetron 16 and the power supply thereof, and by an inclined line 34 lying between the points (Pavg,min; Pmax,min) and (Pavg,max; P1), the value of Pmax,min corresponding to the value of the maximum power associated with the minimum average power Pavg,min and the value of P1 corresponding to the value of the lowest possible maximum power associated with a maximum average power Pavg,max and passing through the line 34, the equation connecting these two points being like: Pmax=a2*Pavg+b2, where the coefficients a2 and b2 are determined so that Pavg never exceeds a limit value of the cyclic ratio Th. This limit value, which is constant regardless of the average power setpoint Pavg, is given by the design of the magnetron 16 and of the power supply thereof.
In a preferred operating mode, the operator enters, on means for entering maximum power values, provided on a man-machine interface, a value of Pmax, i.e. a value Pmax,x. The generator comprises means for producing and indicating on the man-machine interface a possible range PP′ of power setpoints Pavg lying within the abovementioned trapezium. The range PP′ given in
In short, according to this second operating mode, a Pmax,x is preselected, and the value of Pavg is then selected on the line PP′.
To implement the second operating mode, the control device of the invention comprises means for running a computation sequence, the output of said means being connected to means for indicating to an operator the possible range of use of Pavg as a function of the value Pmax which he enters on a means for acquiring a numerical value. If, during step E4, the value Pavg is outside these limits, that is outside the trapezium shown in
The areas of choice of the cyclic conduction ratio Th as a function of the average power setpoint Pavg consumed by the magnetron 16 are shown. The cyclic ratio Th in the third operating mode is determined according to the desired characteristics of the containers after treatment. It is selected in the trapezoidal area bounded by the vertical lines corresponding to a minimum average power consumption Pavg,min (associated with a value of the minimum cyclic ratio Thmin) and a maximum average power consumption Pavg,max by a horizontal line 35 corresponding to the value of the maximum cyclic ratio Thmax not to be exceeded for the operating safety of the magnetron 16 and of its power supply circuit used in the barrier layer deposition machine of the invention, and by an inclined line 36 of which the equation is like Th=c*Pavg+d where the coefficients c and d are determined for a type of magnetron which must not exceed a maximum power Pmax given by the characteristics of the magnetron and its power supply, with an average power Pavg between a minimum value Pavg,min and a maximum value Pavg,max Thus, using this trapezium shown in
Thus, in this third operating mode, once the value of Thx has been selected, the possible range of variation of the value Pavg is shown by the line RR′ in
In short, in this third operating mode Thx is preselected, and Pavg is then selected on the line RR′.
To implement the third operating mode, the control device of the invention comprises means for running a computation sequence, the output of said means being connected to means for indicating to an operator the possible range of use of Pavg as a function of the value Thx which he enters on a means for acquiring a numerical value. If, during step E4, the value Pavg is outside these limits, the control device comprises and activates means for prohibiting the passage to step E6. It is then necessary either to modify the value of Pavg, or to reconsider the value of Th to broaden the window of values Pavg available during step E4. The result is that the device of the invention also comprises means for modifying the value of the cyclic conduction (or repetition) ratio Th of the waveform, means for modifying the value of the power setpoint Pavg and means for selecting the abovementioned first means or second means.
In
The present invention therefore relates, according to one of its aspects, to a device for controlling a high-voltage power generator for magnetron for the cold-plasma deposition of a barrier layer of the invention, of the type comprising:
According to another of its aspects, the invention relates to a machine for depositing a barrier layer on the inside wall of a plastic hollow body by means of a cold plasma which is obtained by assembling a hollow body transfer mechanism, and at least one workstation to apply a cold plasma to the hollow body or bodies which are inserted therein at each operating step of the transfer mechanism of the machine.
This treatment requires the combination at each workstation of at least one magnetron 16 and of the high-voltage generator associated thereto.
The rest of the description will recite examples of application and practical implementation of the method of the invention.
We have seen above that the method according to the invention relates to a method for controlling a high-voltage power supply generated for a magnetron 16 for producing a cold plasma inside a hollow body in order to carry out the deposition of the barrier layer inside said hollow body, the method being characterized in that it consists of selecting (step E2) a generator operating mode from a plurality of operating modes (MODE 1, MODE 2, MODE 3), the modification of the operating mode (MODE 1, MODE 2, MODE 3) of the generator varying at least one coefficient ((a, b, c,); (a1, b1, c1)) defining a maximum power Pmax of the wave of the supply power of the magnetron 16 in relation with an average power setpoint Pavg of the magnetron 16, the magnetron 16 supply wave being repeated recurrently with a cyclic conduction ratio Th depending on the average power setpoint Pavg and/or the maximum power Pmax.
According to a first operating mode of the inventive method, the maximum power Pmax of the wave is predefined according to the power setpoint Pavg.
According to one of the alternatives for implementing this first operating mode, the equation between the average power Pavg and the maximum power Pmax has the parabolic form Pmax=a*Pavg)2+b*Pavg+c, where a, b and c are variable coefficients, the cyclic conduction ratio Th being determined by the equation
Th=100*Pavg*π/(2*Pmax).
In general, and regardless of the generator operating mode, the coefficient a is between (−0.002) and 0.002, the coefficient b is between 0 and 4, and the coefficient c is between 0 and 3000.
More precisely, for the first generator operating mode, a=(−0.0012), b=3.22 and c=247.6.
Thus, for an average power Pavg of 350 W, the maximum power Pmax is about 1230 W and the cyclic ratio calculated is about 45%.
Alternatively, it is also possible to set a generator operating mode with the cyclic conduction ratio Th which is dependent on the average power setpoint Pavg by the equation having the formula
Th(%)=a1(Pavg)2+b1*Pavg)+c1
where a1, b1, c1 are variable coefficients, the maximum power Pmax then being determined by the equation Pmax=π*Pavg/(2*Th). The coefficients a1, b1 and c1 thus also define a relation between the maximum power Pmax and the average power Pavg.
By way of example, the values of a1 may be between (−10−7) and (−10−4), the values of b1 may be between 0.03 and 0.06, the values of c1 may be between 25 and 30. Preferably, a1 is (−5*10−6), b1 is 0.0529, and c1 is 27.85.
Preferably, in an operating mode, for example MODE 1, none of the coefficients ((a, b, c); (a1, b1, c1)) is zero.
In another operating mode (MODE 2, MODE 3) of the generator, at least two coefficients a, b and c are zero.
More precisely, in a second operating mode (MODE 2), the maximum power Pmax is fixed constant, preferably at the value of 2100 W with an upper limit value of the cyclic ratio Thmax of 90%.
According to this second operating mode, the values of the coefficients a and b are zero and the value of c is therefore 2100.
A cyclic ratio Th is thereby obtained that is linearly dependent on the average power Pavg, preferably in the case in which the wave is of a sinusoidal type, Th is about 0.07 Pavg. The value of Th is calculated by the equation Th(%)=100*Pavg*π/(2*Pmax), in the case in which the wave is of a sinusoidal type.
Thus, for an average power Pavg of 350 W, the maximum power Pmax is 2100 W and the cyclic ratio Th is 25%, and the waveform such as shown in
It has been described above and illustrated in
According to a third generator operating mode, the maximum power Pmax is linearly dependent on the value of the average power setpoint Pavg.
In this case, the coefficients a and c are zero and, preferably, the value of b is set at 1.745, hence Pmax=1.745 Pavg.
According to this third embodiment, the cyclic conduction ratio Th is fixed, and preferably fixed at 90%.
Thus, for an average power Pavg of 350 W, the maximum power Pmax is 610 W and the waveform obtained is such as shown in
It has been described above and illustrated in
In general, the coefficients ((a, b, c); (a1, b1 c1)) are determined by treatment tests on a batch of hollow bodies, from which the optimal equation between the average power setpoint Pavg, the maximum power Pmax and the cyclic conduction ratio Th is derived.
In order to test the leak tightness of the internal barrier layer formed with the various generator control modes, comparative tests were conducted on the three modes by injecting an acetylene gas C2H2 into the internal volume of a hollow body, such as a bottle, placed in a cavity. In fact, the device for the deposition of a barrier layer by the formation of a plasma consists of a cylindrical-shaped metal cavity, in which the hollow body can be placed, and of a microwave waveguide containing a microwave antenna connected to the power generator, this cavity itself being connected to a vacuum system and a system for injecting gases, such as acetylene. The setting parameters are an average power Pavg of between 200 W and 450 W, a flow rate of acetylene gas, injected into the internal volume of the hollow body, of between 60 sccm and 160 sccm (standard cubic centimeters per minute) and a deposition time of between 1.2 and 4 seconds. The other parameters, such as the deposition pressure and the pulse frequency, are kept constant.
In each of the following examples, a batch of five bottles was tested for each of the three operating modes, the obtained values of the permeability to oxygen being measured using an Ox-Tran (registered trademark) measurement system, supplying values in cc/bottle/24 h.
The bottles used were PET bottles with a capacity of 520 ml and a weight of 28 g, knowing that the value of the permeability of a PET bottle without coating is 0.04 cc/bottle/24 h.
The setting parameters are the following:
It may be observed that according to these setting parameters, the barrier improvement factors (BIF) are the best for modes 1 and 2.
The setting parameters are the following:
It may also be observed that according to these setting parameters, the barrier improvement factors (BIF) are the best for modes 1 and 2.
The setting parameters are the following:
It may be observed that, according to these setting parameters, the barrier improvement factor (BIF) is the best for mode 2.
Similarly, the efficiency of the three operating modes of the generator according to the invention for the deposition of an internal barrier layer was tested by the successive deposition of two different layers, with a first deposition produced by the injection, into the internal volume of the hollow body, of a gas mixture of HMDSO (hexamethyldisiloxane) and nitrogen N2, and a second, deposition produced by the injection, into the internal volume of the hollow body, of a gas mixture of HMDSO, nitrogen gas N2 and oxygen O2.
The variable parameters tested concern the average power Pavg varying between 200 W and 450 W, the flow rate of HMDSO gas varying from 4 to 20 sccm, the nitrogen flow rate varying from 10 to 100 sccm, the oxygen flow rate varying from 40 to 200 sccm seconds, the deposition time for the first layer varying between 0.5 and 2 seconds, and the deposition time for the second layer varying between 2 to 4 seconds.
The bottles had the same characteristics as previously, that is a volume of 520 ml and a weight of 28 g. The values of permeability to oxygen obtained were measured using an Ox-Tran (registered trademark) measurement system, supplying values in cc/bottle/24 h, knowing that the value of the permeability of an uncoated PET bottle is 0.04 cc/bottle/24 h.
Three examples of comparative tests will be shown below for the three operating modes of such a two-layer barrier layer deposition with a step 1 for the deposition of the first layer and a step 2 for the deposition of the second layer.
The results obtained are given in the table below
The results obtained are given in the table below
The results obtained are given in the table below
It may thus be observed that in examples 4 to 6, the three operating modes are approximately equivalent, even though mode 2 is less satisfactory in terms of BIF in example 4 and mode 3 in example 6.
It is thus possible according to the method in accordance with the invention to rapidly and simply select the characteristic parameters of an optimal wave for the formation of an internal barrier layer in a hollow body and varying the variable coefficients relating the maximum power Pmax, the average power Pavg and the cyclic recurrence ratio Th.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0653304 | Aug 2006 | FR | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/FR2007/051768 | 8/2/2007 | WO | 00 | 2/5/2009 |
