EP1317292A2

EP1317292A2 - Plasma sterilisation system

Info

Publication number: EP1317292A2
Application number: EP01972154A
Authority: EP
Inventors: François PERRUCHOT; Marie-Pierre Jaffrezic; Philippe Destrez; Séverine BOUSQUET
Original assignee: Absys
Current assignee: Absys
Priority date: 2000-09-15
Filing date: 2001-09-13
Publication date: 2003-06-11
Also published as: WO2002022180A3; WO2002022180A2; FR2814079B1; US20040037736A1; FR2814079A1; AU2001291945A1; JP2004508143A

Abstract

The invention concerns a plasma sterilisation system in the presence of humidity from a non-biocidal gas containing oxygen and nitrogen of at least an object placed outside the discharge in a sealed treatment chamber substantially subjected to atmospheric pressure, said method comprising the following steps: introducing the humidified non-biocidal gas into the treatment chamber, generating a first plasma discharge A for a specific duration ensuring the efficacy of the sterilising species generated during the following phase in the entire chamber; generating a second plasma discharge B for a specific duration ensuring sterilisation of said object and rinsing the treatment chamber for a specific duration to ensure a non-polluting atmosphere when the chamber is subsequently opened. Preferably, the first plasma discharge and the introduction of humidity are simultaneous and the first and second plasma discharges can overlap such that the generation of the second plasma starts before the end of the first plasma discharge. The invention also concerns various devices for implementing said method in particular for sterilising all types of medical objects.

Description

Plasma sterilization system

The present invention relates to the general field of sterilization of objects and surfaces of any kind and any shape and it relates more particularly to a process and various devices for plasma sterilization operating at room temperature and at atmospheric pressure.

PRIOR ART Sterilization corresponds to a very precise level of quality in the medical and food industries. In the medical environment, it designates a destruction of all microorganisms whatever their nature. According to the European Pharmacopoeia, an object can be considered sterile if the probability that a viable micro-organism is present is less than or equal to 10 ^"5. The sterilization time is the time necessary to sterilize an object" normally contaminated " , that is to say containing 10 ⁶ bacterial spores. Thus, the sterilization of an object corresponds to a reduction in the initial population of bacterial spores present on this object from 10 ⁶ spores to 10 ^"6 spores is a logarithmic reduction 12 decades. The time required to reduce a decade is by definition called decimal reduction time, denoted D. It is a fundamental variable characterizing a sterilization process.

Currently, there are many methods for making and keeping sterile objects. The article by Philip M. Schneider published in volume 77 of the Tappi Journal of January 1994 on pages 115 to 119 gives a relatively exhaustive overview. However, Mr. Schneider ends his remarks on the observation that today there is no ideal sterilization method at low temperature (less than 80 ° C), that is to say that is of great efficiency, fast action and high penetration, which is also non-toxic, compatible with many materials including organic materials and which can be implemented simply with low costs.

In addition, the sterile state of an object must be maintained by a specific packaging which must be compatible with the sterilization method used (permeable to the sterilizing agent) and prevent penetration of microorganisms during the transport and storage phases, in order to guarantee the sterility of the instrument during its next use.

Current sterilization processes are mainly based on the effect of heat or the action of block gases.

The autoclave, which relies on the action of moist heat at high temperature (at least 121 ° C), is the most efficient and cheapest process to use, but it does not allow sterilization of heat-sensitive devices increasingly present, especially in the medical field.

Gas sterilization processes (ethylene oxide, formaldehyde, hydrogen peroxide) use the biocidal nature of a gas placed in a sterilization enclosure and allow low-temperature sterilization of heat-sensitive devices. However, they have many drawbacks: the toxicity of the gases considered, which imposes complex procedures for use and control; the obligation, in certain cases (with plastic materials for example), to carry out a phase of desorption of the toxic gas after the sterilization phase; finally the length of the treatment which often requires several hours. In addition, the limited killing effect on certain bacterial spores (such as Bacillus stearothermophilus spores) should be noted.

Also, a known improvement in these sterilization processes with biocidal gases consists in carrying out the treatment at low pressure (a few Torrs), which makes it possible to promote the diffusion of the gas or the vaporization of an additional biocidal liquid throughout the enclosure. sterilization. Likewise, these low-pressure sterilization processes can be optimized by creating cycles of alternation between phases of reduction or increase in pressure and phases of plasma treatment, as shown in particular in patent application FR 2 759. 590 filed by SA Microondes Energie Systèmes.

Low pressure plasma sterilization processes are also known which optionally make it possible to combine the sterilizing effects of biocidal gas at low pressure with the formation, in a plasma, from a biocidal gas mixture such as H2O2 or a non-gas mixture. biocide (in general simply O ₂ , H ₂ , H ₂ O, N2 or a rare gas such as Argon) of reactive species (creation of 0 ° and OH ° radicals ionized and / or excited species). Low pressure plasmas include, in the majority of cases, microwave or radiofrequency plasmas.

Sterilization by low pressure plasma can be very effective in the space where the plasma is created (inter-electrode space), but, apart from the fact that the sterilization zone is then very small (about a few cm in height), the characteristics of the plasma depend very strongly on the dielectric constant, the nature and the size of the object to be sterilized. In this case, the plasma prevents a truly uniform treatment over the entire surface and has a highly corrosive action on the objects to be sterilized.

To improve such a process, it is necessary to dissociate the plasma production and treatment zones (sterilization is then said to be carried out in post-discharge) in order to avoid excessive interaction between the plasma and the object to be sterilized. This separation of the plasma production zone and the sterilization zone is easy in a low pressure process because the low pressure limiting the recombination of unstable species, the lifetimes of the radicals produced by the plasma at these pressures (of approximately 1 Torr) are important, which allows them to reach the objects to be sterilized.

The drawbacks of low pressure plasma sterilization processes are, however, still numerous and ultimately quite close to those existing in gas sterilization alone: the high cost of the complete system containing a vacuum-resistant enclosure and a generator. plasma; the complexity of the devices implementing these methods which limits the possible applications; the increase in treatment time due to the procedures associated with treatment at low pressure (the times required to evacuate the enclosure, often of large volume, then return to atmospheric pressure increase the treatment time); the impossibility of sterilizing wet objects; and incompatibility with certain materials.

Another known method using the post-discharge principle consists in carrying out an ozone treatment at atmospheric pressure using an appropriate device called an "ozonator". This treatment is similar to a sterilization by plasma in post-discharge at atmospheric pressure whose carrier gas does not contain moisture to promote the creation of ozone contains oxygen. However, the biocidal action of ozone, which is mainly used for the disinfection of water and gas waste, is quite limited in terms of sterilization. To obtain better performance, it is generally necessary to add to ozone (O ₃ ) another disinfecting agent (for example CI0 _{3 in} order to form CI0 ₃ which has a bactericidal action in the gas phase). One can also carry out a humidification of the ozone gas at the outlet of the ozonator or else simply wet the objects to be sterilized to facilitate the biocidal action of this ozone gas as illustrated in US Pat. No. 5,120,512 (Masuda). In general, for plasma processes using simple non-blocking gases, the separation between the plasma production zone and the treatment zone limits the efficiency of the process because only the medium and long-lived species are still active at the level of the object. However, these species being less reactive than those with a short lifespan, it is necessary to increase their concentration and the treatment time. For example, it is known that nearly 3 hours of treatment are necessary to obtain the sterilization of Bacillus subtilis spores in the presence of moisture for an ozone concentration of 1500 ppm. The ozone concentrations used in ozonizer sterilizers are much higher, typically between 10,000 and 80,000 ppm. Such a level of production requires the use of complex devices while the high concentration of ozone increases the irreversible degradation of the surfaces and materials of the objects to be sterilized. In addition, the production of ozone in high concentration makes it necessary, due to the regulations, the recourse at the output of the system to a particularly effective ozone-destroying device of the type of those with catalysis or by thermal way.

Also, in the patent application PCT / FROO / 00644 filed on behalf of the applicant, the inventors proposed a new sterilization process at atmospheric pressure and at room temperature using a plasma in post-discharge. This process which operates from a non-biocidal gas mixture containing nitrogen and oxygen (for example air), the sterilization being carried out in the presence of an amount of humidity greater than 50% RH , avoids the use of complex vacuum manufacturing devices and the use of biocidal gases. Its simplicity allows its use for various configurations allowing to fragment the sterilization. Its operating principle is based on a cycle in three successive phases illustrated in FIG. 6. The first phase Phi corresponds to the introduction of the non-biocidal gas mixture containing a high percentage of humidity into the treatment enclosure. The second phase Ph2 starts when the humidity level in the enclosure is sufficient and corresponds to the sterilization phase proper from a plasma discharge creating species having a sporicidal action. The duration of this phase is fixed by the desired level of decontamination. The last phase Ph3 corresponds to the rinsing of the enclosure which marks the end of the treatment cycle.

The effectiveness of this post-discharge process is based on the possibility of propagating the active species created by the plasma source to the surface to be sterilized. The propagation of the species from one point to another of the enclosure involves both the effective propagation time and the surfaces encountered between the two points. However, if such a method is generally satisfactory, under certain specific conditions of use, in particular for the treatment of large volume enclosures or objects of elongated shape, it turns out to be necessary either to distribute the number of sources along the sterilization zone so as to reduce the maximum distance to a source for each point on the surface, ie to provide within the enclosure suitable propagation zones for propagating sterilizing species. However, both of these two solutions have the consequence of significantly increasing the cost of the treatment enclosure by imposing in particular a high voltage connection between the different plasma sources or a complex geometry for the enclosure.

Object and definition of the invention

The object of the present invention is therefore to propose an improved sterilization process making it possible to optimize the sterilization time for all configurations, including for large volume enclosures or elongated objects without increasing the cost of the pregnant. An object of the invention is also to propose an improved process making it possible to reduce the number of plasma sources necessary for sterilization without making the manufacture of the enclosure more complex. Another object of the invention is to propose a method presenting a sporicidal efficacy in reasonable time at low temperature. Yet another object is to propose a non-polluting process avoiding any manipulation of dangerous products unlike the simplest methods known for sterilization at low temperature. According to the invention, there is provided a method of sterilization by plasma in the presence of moisture from a non-biocidal gas containing oxygen and nitrogen of at least one object placed outside the discharge in a sealed treatment enclosure subjected substantially to atmospheric pressure, characterized in that it comprises the following stages:

- introduction of the humidified non-biocidal gas into the treatment enclosure,

- creation of a discharge from a first plasma A for a determined period, making it possible to guarantee, throughout the enclosure, the effectiveness of sterilizing species created during the next phase,

- creation of a discharge of a second plasma B for a determined period allowing the sterilization of said object,

- rinsing of the treatment enclosure for a determined period so as to guarantee a non-polluting atmosphere during the subsequent opening of the enclosure.

Thus with this invention, it is possible to treat elongated objects or more generally large volume speakers with a limited number of plasma sources. Said determined durations are also calculated as a function of the volume of the treatment enclosure and of the objects to be treated.

Advantageously, the end of the rinsing step is detected by crossing a minimum threshold of a parameter. Advantageously, this parameter is the relative humidity and the ozone concentration measured by a multi-parameter sensor placed at the outlet of the treatment enclosure.

According to a preferred embodiment, the plasma discharge A and the introduction of humidity are simultaneous and the discharges of the first and second plasmas overlap so that the creation of the second plasma B begins before that of the first plasma A. The discharges of the first and second plasmas can use the same plasma source. Preferably, the discharges of the first and second plasmas are different in nature to allow separate optimization of each phase.

Advantageously, the flow rate of the non-biocidal gas is different between the different phases. Advantageously, the choice of discharge regimes for the first and second plasmas is determined by the elementary pattern of the voltage signal (alternating, damped or continuous alternating), the frequency of repetition of the pattern and the total setpoint current. Advantageously, the detection of the peak current makes it possible to control the speed used. Preferably, this detection is done with a bandwidth of the order of the frequency between the pulses.

Advantageously, the repetition frequency of the patterns or a lag time between the elementary patterns is used to limit the rise in temperature in the reactor while maintaining the same discharge regime.

In an alternative embodiment, the increase in temperature of the object is compensated for by the thermalization of an evaporative humidifier at a temperature slightly lower than that of this object. In another alternative embodiment, this compensation is obtained by controlling the effectiveness of a vaporizer so as to keep the humidity constant at the level of the object.

Advantageously, the high voltage supply is produced from a low voltage supply drawn from a transformer used as a filter and as a voltage booster. Advantageously, controlling the repetition of the low voltage pulses makes it possible to introduce an adjustable latency time. In a first mode of use, the repetition frequency of the low-voltage pulses is lower than the resonant frequency of the transformer. In a second mode of use, the repetition frequency of the pulses is equal to the resonant frequency of the transformer.

In a first embodiment, the supply is regulated on the basis of a measurement of a current, preferably direct for a supply of direct voltage, synchronous for a supply of alternating voltage, measurement carried out through a resistor. Current can also be measured indirectly by measuring the charge of a capacitor. In the case of a DC voltage supply, the discharge of the capacitor is ensured by periodic earthing.

In another embodiment, the power supply is regulated on the basis of a peak current measurement. Advantageously, the signal used for regulation is smoothed with a time constant greater than 100 ms, preferably 1 s.

The electrodes are produced from a blade comprising one or more points placed parallel to a flat or cylindrical surface serving as a counter-electrode. In a preferred embodiment, the number of tips is chosen so as to facilitate the use of the different discharge regimes desired during the treatment.

In a preferred configuration envisaged for the device, it comprises several treatment chambers, each treatment chamber comprising at least one plasma production zone connected in a fixed manner to at least one sterilization zone, the production zones of plasma being connected to a common central unit containing at least the first source of non-biocidal gas, the humidification chamber, the system for recovering gaseous residues and as many high-voltage power supplies as there are outputs allowing the speakers to be treated simultaneously by applying different discharge regimes.

In one embodiment, the sterilization area is slightly pressurized to allow flow into fine capillaries.

It includes a multi-parameter sensor for each connection channel allowing the composition of the gas leaving an enclosure to be checked before filtration.

Brief description of the drawings

Other characteristics and advantages of the present invention will emerge more clearly from the following description, given by way of non-limiting illustration with regard to the appended drawings in which:

FIGS. 1a, 1b and the are chronograms illustrating the improved plasma sterilization method according to the invention, FIG. 2 is a block diagram of a plasma sterilization device according to the invention,

FIG. 3 is a block diagram of a high voltage power supply adapted to the device of FIG. 2, FIG. 4 illustrates an exemplary embodiment of the plasma sterilization device of FIG. 1,

FIG. 5 shows an exemplary embodiment of a treatment enclosure in accordance with FIG. 1,

FIG. 5a is an exploded view of FIG. 5 illustrating a particular configuration of the discharge zone, and

- Figure 6 is a timing diagram of the different stages of a plasma sterilization process of the prior art.

Description of a preferred embodiment The invention relates to an improved sterilization method having a sporicidal efficacy tested in particular on bacterial spores considered by the European Pharmacopoeia as the most resistant: Bacillus subtilis and Bacillus stearothermophihis.

Generally, this process uses a gaseous mixture containing oxygen and nitrogen from which a low temperature plasma is created, the chemical species of which have a sterilizing action on the object to be treated in the presence of moisture. . The object to be treated is placed outside the space where the discharge takes place and the treatment is carried out at atmospheric pressure. Plasma is a gas partially activated by an electromagnetic source of sufficient energy. The species created in the plasma are ionized (molecules or atoms), neutral (such as radicals) or excited species. These gaseous species have an increased reactivity which allows them to interact with the surfaces of the object or objects to be sterilized and thus to destroy the microorganisms present on these surfaces. At atmospheric pressure for a plasma created from a simple non-biocidal gas, the most reactive species are those with the shortest lifespan, this efficiency strongly depending on the distance between the area of creation of the plasma and the object. . According to the invention, it is proposed to modify the processing cycle as described in the aforementioned PCT / FROO / 00644 request so that, during object processing of elongated shape or more generally of large volume enclosure, the efficiency is guaranteed throughout the volume of the enclosure with a minimum number of plasma sources. It is proposed to adapt the implementation to this new treatment cycle, in particular by developing a specific high voltage power supply.

A preferred example of a treatment cycle in accordance with the invention is illustrated in Figures la to le. This cycle is always broken down into three successive phases, but these phases are now organized differently with: a first phase Pha of bringing the chamber into equilibrium comprising a discharge of a first plasma A, a second phase Phb of treatment workforce comprising a discharge of a second plasma B and a third and final rinsing phase Phc. The reduction in the total cycle time involves optimizing each of these three phases, taking into account its effect, in particular on the possibly next phase.

The objective of the first phase Pha is to bring the entire enclosure under conditions allowing the species that will be created during the next phase Phb to spread over all of the surfaces to be treated and to have an action sporicide in reasonable time. It includes, as in the aforementioned process, necessarily the homogeneous introduction of moisture which is a minimum condition necessary for the creation of species during the second Phb phase. However, it also comprises a concomitant discharge or not of a first plasma not necessarily having a significant sporicidal action but essential to ensure the equilibrium of the enclosure before the start of the next phase. A simultaneous start of the first plasma and the introduction of humidity also makes it possible to significantly reduce the total treatment time as illustrated in FIG. 1b. The duration of this phase is determined according to the volume of the enclosure and the objects to be sterilized.

Indeed, as shown in the following table 1 resulting from tests carried out by the inventors, with the method of the aforementioned international application, in the case of the sterilization of objects of very elongated shape such as the endoscope or large volume, it takes a determined time TO before the plasma has a sporicidal effect. This time TO does not depends not only on a resistance time associated with the spores but also on the nature of the walls of the enclosure.

Table 1: TO stabilization time before sterilization (excluding humidity) in a tube with an internal diameter of 25 mm

There is therefore thus a critical distance between the source and the surface to be treated from which this phenomenon of absence of immediate sporicidal effect appears. This stabilization time TO which must be taken into account to guarantee the sterile state at the end of the cycle therefore increases the total treatment time.

The second Phb phase is the effective treatment phase, lasting 12 D in the case of sterilization. D is measured from tests carried out for the most unfavorable conditions on the microorganisms considered to be the most resistant. The second plasma is optimized to have maximum sporicidal action by limiting the degradation of materials. If the gas production means allow, this second phase Phb can be advanced and therefore begin before the end of the first phase Pha, as illustrated in FIG. Le, in order to guarantee optimal filling of the plasma B before l plasma stop A. In this configuration, the second phase Phb then has a duration greater than 12D.

The last phase must allow the enclosure to return to an atmosphere compatible with the storage of the enclosure and its subsequent opening by circulation of the non-humidified gas.

A block diagram of a plasma sterilization device implementing the improved method according to the invention is illustrated in FIG. 2. This device is organized around a treatment enclosure 10 separated into two zones: a production zone plasma 10a inside which, by a discharge between two electrodes, is created a plasma and a sterilization zone 10b where the object to be treated is placed. The discharge is produced from a non-biocidal gas mixture supplied by a gas source 12 via a humidification chamber 14. The humidification chamber has at least two channels, one at maximum humidity and one at minimum humidity. , known as the dry process. The choice between the two routes is made according to the current phase: wet route during the Phb phase and at least part of the Pha phase, dry route during the Phc phase. This treatment enclosure is completely closed.

The gas mixture contains oxygen and nitrogen and its composition may vary depending on the nature of the object to be sterilized. The level of oxygen contained in the mixture depends on the aggressiveness of the mixture vis-à-vis the materials of the objects to be sterilized. The gas mixture must contain at least 10% oxygen and 10% nitrogen to ensure an acceptable sporicidal effect as shown in the following table (the samples contain bacterial spores of subtle Bacillus / s):

Table 2: comparison of the efficiency of a discharge from a carrier gas containing argon and nitrogen and associated ozone measurement (T means sample at the control level).

Advantageously, this mixture can be ambient air obtained from a compressor. The relative humidity level in the sterilization zone during the second Phb phase, therefore at the level of the objects to be treated, is between 50% and 100%, advantageously greater than or equal to 70%. The following table 3 shows the importance of this parameter:

Table 3: comparison of the efficiency at an identical time for a RH of 20% to 80%.

The flow of entry of the gas mixture into the treatment chamber 10 is adjusted as a function of the size and the quantity of the objects to be sterilized and of the phase in progress, by a control device (for example a valve 16) disposed at the outlet of the gas source 12 and allowing control of its flow speed and its concentration. The object to be sterilized 20 is placed on a support, which must allow the circulation of the sterilizing agent over its entire surface, in the sterilization zone 10b, that is to say outside the plasma production zone. (inter-electrode zone of creation of the discharge). In the example illustrated, the supply is made by a wet gas mixture and the plasma production zone comprises on the one hand an inlet orifice for the arrival of the carrier gas and on the other hand two electrodes, an electrode high voltage 24 supplied by a low frequency high voltage generator 26 and a ground electrode 28, intended to produce between them an electric discharge known as a "crown" discharge. The corona discharge is characterized by the use of two electrodes having a very different radius of curvature. The increase in the electric field near the electrode with a small radius of curvature makes it possible to decrease the voltage necessary for the appearance of the discharge while using a voltage supply which can be low frequency since it does not use the effect of resonance at the electrodes. The orifice for the arrival of the carrier gas 30 is preferably located near the electrodes 24 and 28 to optimize its passage through the inter-electrode space, the production of the plasma being located in this inter-electrode space. A gas outlet orifice 32 is located in turn in the sterilization zone 10b downstream of the object to be treated with respect to the natural direction of flow of the gas.

A humidity and temperature sensor 40 is placed at the outlet of the humidifier to check the quantity of water vapor present in the gas at the inlet of the discharge zone 10a. A bacteriological filter 42 is placed between the sensor and the inlet 30 to guarantee the sterility of the injected gas, in particular during the last Phc rinsing phase.

The gaseous residues (effluents) resulting from the discharge are evacuated by the outlet 32 to a recovery system 22 so as not to exceed the limit concentrations fixed by the regulations. In the case of ozone, for example the average exposure value admitted in a workplace over 8 hours is 0.1 ppm according to the standard of the Occupational Safety Health Administration). The gas leaving the recovery system 22 is analyzed, for example with an ozone sensor 44 to verify the proper functioning of the filtering before discharge to the outside. A multi-parameter sensor 46 is placed before the filter 42 to analyze the gas leaving the reactor 10. Preferably, this sensor is sensitive to the temperature, humidity and the chemical composition of the gas, for example in ozone.

The measurements coming from the sensors 40, 44 and 46 and from the source 26 are centralized towards a control member 50 which controls the passage between the different phases of the cycle by changing the setpoints sent to the high voltage source 26, the valve 16 and l humidifier 14.

The first and second phases of plasma creation having a different role: balancing for the first plasma by creating the chemical conditions favorable to sterilization, sporicidal effect for the second plasma, it is preferable to be able to have different types of discharge regimes corresponding to different chemical productions in order to optimize the process. To obtain these different regimes, it is possible to use different plasma sources. The general objective of the various solutions proposed below is to increase the number of discharge regimes achievable from a given configuration to allow maximum optimization of the process and the means enabling their control. For example, for a given type of high voltage signal defined by its polarity, its shape and its frequency, the signal associated with given electrodes, the discharge regime and the production of chemical species depend on the intensity and the shape current. The total current measured on the ground electrode contains different components associated with different physical effects. For example, for a positive DC voltage, associated with a tip-plane type geometry, the current is, below a voltage threshold, composed only of a DC component attributed to a so-called "glow" regime. To a higher voltage is added a so-called pulse current composed of pulses of high amplitude, typically a few milliamps and of short duration, typically 100 ns, associated with the regime known as “streamers”. A higher voltage gives rise to a direct current of electric arc corresponding to the appearance of a conductive channel in the gas.

The use of an alternating voltage makes it possible to place a dielectric on one or the other of the electrodes, preferably on the plane electrode and to delay the passage to the electric arc. This is called a DBD (Dielectric Barrier Discharge) discharge. Intermediate energy regimes then appear which make it possible to cross different zones of chemical production. New pulses then appear of very high amplitude, typically a few hundred milliamps and of short duration, typically 100 ns. This type of DBD discharge therefore offers greater flexibility in choosing the type of diet. Likewise, the production of chemical species by the plasma strongly depends on the presence of the impulse current. For a DC voltage discharge, the amount of charge associated with the pulse current is of the same order of magnitude as the amount of charge associated with the direct current. In DBD discharge, the amount of charge associated with the synchronous current can remain much greater than the amount of charge coming from the pulses, particularly in the low power regimes used for the process discussed. The effective impedance of the discharge giving the relationship between current and voltage can change over time and is highly dependent of the geometry of the electrodes. The regulation of the high voltage supply is therefore preferably done at constant current to maintain the same discharge regime and the same production of chemical species in order to ensure a constant sterilizing effect. For linear electrodes, the discharge regime and the production of chemical species are a function of the current per unit length.

To determine the regime used, it is theoretically necessary to use a very high frequency acquisition on a large number of points in order to be able to differentiate the different components of the current. The inventors have shown that it is in practice possible to use a few simpler and therefore more economical measurements to measure the direct or synchronous current and the peak current associated with the different types of discharge current whose role is predominant in the method of the invention, even for the low power systems used. This is particularly true in DBD discharge even when the amount of associated charge is small. The measurement of the peak current in this case is therefore particularly suitable since it makes it possible to obtain a signal very sensitive to the presence of this type of pulses, which a simple measurement of power or average current does not allow. In this case, it is therefore particularly useful to use the peak current as a minimum as a control measure, at best as a regulation parameter. In this case, it is necessary to provide a sufficient integration constant not to take account of "natural" fluctuations in the amplitude of the pulses. It is also possible to use an indirect measurement of the current by measuring the charge of a capacitor. This measurement is direct in the case of an alternative supply since the discharge of the capacitor is automatic. In the case of a DC voltage supply, it is necessary to provide for a periodic discharge of the capacitor.

Finally, a control measurement can be carried out by counting for a given period the number of impulse discharges detectable by current peaks of a few milliamps and of short duration (typically 100 ns), the density over time of these current peaks serving determining the regime used. Of course, the measurement system must be fast and precise enough to give the exact number of discharges.

The voltage signal applied to the high voltage electrode can be continuous or in slots, of positive or negative sign, alternating or even pulsed depending on the discharge regime chosen for each of the phases. It is therefore preferable for the generator to have a solution offering maximum modularity in terms of amplitude and shape.

By way of example, the generator can be produced as described in FIG. 3. A transformer 100 having a resonant frequency located in the low frequencies, typically less than 100 kHz, is supplied by a low-voltage DC source 102 operating from preferably as a current source via a transistor used as a controlled switch 104. The duration of the pulse 106 is adjusted so as to optimize the breaking current, the transformer serving both as a voltage step-up element and as a filter and providing a elementary sinusoidal pattern. The repetition frequency of the well is determined by the well generator 114 according to the instruction supplied by the control member 50. By repeating this well at the resonant frequency of the transformer, a quasi-sinusoidal signal 108 is obtained. decreasing the repetition frequency, a pulsed supply is obtained with an elementary pattern comprising a damped sinusoid 110. To obtain a DC voltage supply, it is necessary to place a rectifier system at the transformer output. It is also possible in all cases of continuous, sinusoidal or damped sinusoidal pattern to introduce a lag time between the patterns corresponding to a zero voltage at the transformer output to obtain a signal comprising an envelope of rectangular type, for example of type 112 for a sinusoidal pattern. The amplitude of the signal depends on the value of the DC voltage applied to the transformer. The regulation can be carried out on the basis of a current or voltage measurement at 118, the comparison of which with a setpoint inside a comparator 116 makes it possible to act on the low voltage source 102. The inventors have been able to show that this type of power supply, very simple and low-cost in design, provides a stable discharge. It also has the great advantage of allowing the choice by simple programming between different types of high voltage signals, while remaining very simple. Within the same discharge regime, as long as the chemical saturation resulting from the recombination of the unstable species is not reached, the increase in the current makes it possible to increase the production of species. A potential optimization of the efficiency for a chosen discharge regime therefore requires an increase in the total current without regime change.

The simplest configuration for obtaining a crown discharge is a configuration known as point-plane in which the set of electrodes is composed by a point placed perpendicular to a plane. This configuration makes it possible to determine a relationship between current and electric field characterizing the different discharge regimes. By extension of a tip-yaw configuration, it is possible to multiply the number of tips by placing them on the same blade parallel to the plane. For a discharge regime defined from the tip-plane configuration, it is thus possible to increase the total current at constant voltage without changing the regime by increasing the number of tips. This increase in current at constant discharge and constant voltage is possible as long as the tips are electrically independent, that is to say as long as their separation distance remains greater than 2d, d being the inter-electrode distance. Beyond this density, the total current saturates at constant electric field.

Likewise, the inventors have been able to show that it is possible to increase the maximum total current at a fixed discharge rate by increasing the density of the tips beyond the electrical dependence. For example, for a DC voltage discharge, it is possible to postpone the transition to the arc which corresponds to a net change in speed by increasing the density of the tips. Thus, it was possible to obtain a current density in streamer regime of the order of 162 μA / cm for a distance between centers of 1 mm with an inter-electrode distance of 10 mm, while this density is limited at 70 μA / cm for a distance between centers of 10 mm as illustrated in table 4 below:

Table 4: Effect of the number of points on the maximum current before going to arc for an inter-electrode distance of 10 mm.

It should be noted that the transition to the arc poses stability problems, increases the problems of electromagnetic compatibility and mechanical resistance of the electrodes and that this therefore corresponds to a regime more difficult to use.

The increase in the density of the tips therefore makes it possible to extend the voltage ranges corresponding to each discharge regime. This increase in the operating range corresponds to an increase in the stability of each regime, which reduces the constraints on regulation. The density limit is given by the manufacturing constraints linked to the electrode and by the maximum voltage that can be delivered by the generator.

Tests carried out by the inventors have shown that the higher the relative humidity at the level of the object, the shorter the sterilization time (see in particular table 3 above). On the other hand, as shown in the following table 5, a rise in temperature of the surface to be sterilized also results in a reduction of the sterilizing effect.

Table 5: effect of heating the sample. It is therefore necessary to maintain the relative humidity, measured at the temperature of the object if it is different from the temperature of the humidification chamber, above a critical value estimated at around 50%. It is interesting to note that it is not necessary to humidify the objects or to cause uniform condensation: the object and the humidifier can remain at the same temperature. The inventors have further verified that sterilization is effective even on wet objects.

The electric discharge produces a power which dissipates on the level of the gas of the zone of discharge and the electrodes. This heating can cause a rise in temperature of the surfaces to be sterilized and therefore suppress the sporicidal effect by reducing the local relative humidity as has been shown with table 3 above. There is therefore a maximum power not to be dissipated depending on the configuration, in particular for the second plasma discharge during the second phase Phb. However, certain discharge regimes are not electrically attainable without a certain minimum instantaneous electrical power. This is for example the case in DBD type discharge: there is necessarily a minimum power to be dissipated by the synchronous current before the appearance of the high amplitude pulses associated with this regime.

A first solution consists in reducing heating by using a pulsed alternating supply or with a rectangular envelope making it possible to reduce the average dissipated power while retaining sufficient instantaneous electric power.

A second solution consists, when the humidifier is an evaporative humidifier, of maintaining the temperature of the humidifier at a temperature close to and slightly below the temperature of the surface to be sterilized so as to maintain a constant relative humidity at the level of the 'object. This configuration only applies in the case of simple surfaces whose temperature can be measured directly or estimated from the temperature of the surrounding gas. In addition, it must be ensured that there is no cold spot between the humidifier and the discharge area. Another solution is to use a vaporizing humidifier to supersaturate the gas with water so that the relative humidity after heating is sufficient. In this case, the discharge also serves as an evaporator for the micro-droplets created by the humidifier: the vaporization is adjusted so as to maintain the humidity at the temperature of the object at a sufficient level. This configuration requires precise control of the temperature gradients and only works if the quantity of microdroplets required does not exceed the limit acceptable by the discharge.

The first phase of bringing the reactor into equilibrium ends when the sterilizing action of the species produced by the second plasma can effectively begin, that is to say when the chemical conditions are favorable for sterilization, both in terms of humidity and of more general chemical equilibrium. The supply of water vapor is provided by the gas flow passing through the humidification chamber: it is therefore limited by the capacity of the humidification chamber to humidify a given flow. The effect of the discharge of the first plasma is limited by the maximum production of the discharge zone which is a function of the flow. In the general case, there is therefore an optimum flow rate which must take account of the two objectives. In some cases, the introduction of moisture and the discharge of the first plasma may not be simultaneous. At the end of the Pha phase, the humidity measured at the sensor 46 makes it possible to verify that the necessary humidity threshold is reached.

The discharge of the first plasma is chosen so as to minimize the time for bringing the enclosure into equilibrium. The power must be chosen so as to guarantee an acceptable temperature at the end of the treatment cycle. This can for example imply applying a decreasing power over time to allow a return to a lower temperature.

The discharge of the second plasma is chosen according to its sporicidal action in the presence of moisture. Its power is limited to guarantee an acceptable temperature throughout its duration. Among the various possibilities, the inventors have shown, for example (see Table 6 below) that the streamer regime in continuous voltage or the regime in pulsed DBD discharge had a sporicidal action leading to decimal reduction times D measured on bacterial spores of Bacillus subtilis of the order of a few minutes for powers less than 1W / L

Table 6: comparison between the DC voltage discharge and the DBD discharge.

The sensor 46 makes it possible to verify that the humidity is sufficient throughout the course of the Phb phase.

It should be noted that, in the particular case where the discharges of the Pha and Phb phases can be produced at the same time (different sources, superimposable electrical signals, etc.), it may be advantageous to ensure an overlap of the Pha and Phb phases , the Phb phase starting before the end of the Pha phase. Thus, the filling of the treatment enclosure with the gas of the Phb phase is completed at the end of the Pha phase and the Phb phase is then immediately operational. Finally, the third phase Phc is a rinsing phase carried out from the non-humidified gas. The main parameter is therefore the flow depending on the volume of the enclosure.

The multi-parameter sensor 46 placed at the outlet of the treatment enclosure 10 makes it possible to determine the end of the Phc phase corresponding to the return to a chemical composition acceptable for storage. Preferably, the criterion is based on the measurement of humidity and ozone provided by this sensor. The ozone sensor is preferably a sensor operating in an intermediate range, typically 1 to 3000 ppm

A first exemplary embodiment of a sterilization device in accordance with the principle stated above is illustrated in FIG. 4. It is a modular assembly with a central unit 60 to which are connected different types of treatment chambers 74- 80, 120. This modular configuration makes it possible to process, simultaneously or not, a set of speakers adapted in number, shape and volume to these objects from a single central unit comprising one or more high voltage power supplies and a single gas management system (ensuring supply and recovery) contained in the central unit. The use of several high voltage power supplies and several humidification chambers simplifies the regulation system and allows asynchronous use of different boxes and the use of several multi-parameter sensors makes it possible to control the composition of the gas recovered before filtration to determine or check the time associated with each phase. The sterilization zone can be of variable size or standardized according to the needs of the user. By adapting the shape and volume of the area to the objects to be sterilized, it is possible to optimize the circulation of the sterilizing agent (its flow speed and its concentration) around the objects and thus to ensure a homogeneous treatment. The gas after treatment is then returned to this central unit by one or more gas discharge inlets. This type of device can be proposed because the low cost of implementing the method makes it possible to multiply the treatment zones and therefore to fragment the volumes treated.

This modular assembly comprises a common central unit containing the source of gas mixture, one or more humidification chambers and one or more high voltage power supplies. The central unit 60 comprises one or more gas outlets (for example 62) and a corresponding number of high voltage outlets (for example 64) supplying one or more treatment chambers each comprising a plasma production area 68, 70, 72 corresponding to the plasma production zone 10a and supplying sterilizing gas to a sterilization zone 76, 78, 80 corresponding to the sterilization zone 10b containing the objects to be treated. The plasma production and sterilization zones can form two distinct zones of the same enclosure (for example enclosures 74 and 130), or they can each integrate a separate enclosure then called plasma production enclosure (in the case of enclosures 68, 70, 72) or sterilization enclosure (for enclosures 76, 78, 80). Advantageously, all or part of the entire device is placed in a Faraday cage to limit the interference created by the discharge. Indicating and control means 84, 86, 88, 90 arranged on the central unit 60 opposite the corresponding speakers with which they are associated make it possible to ensure individual control of each enclosure by ensuring the start of the sterilization cycle and the adjustment of the time of the different phases of the treatment, by adjusting the set flow rate, the appropriate regulation current and the signal form voltage, and possibly by defining the composition of the gas mixture to be used. The volume of the enclosure determines the number and size of the plasma sources used: it therefore has a direct influence on the flow and current setpoint. This setpoint also depends on the discharge regime chosen, and therefore on the phase in progress. The follow-up of the various commands is ensured by the output of a label printed 94 on a printer 96 integrated into the central unit 60. For each enclosure, which carries a specific identification number, it is thus possible to mention on this label the date of treatment and the parameters of the sterilization cycle, including its duration. The loudspeakers can be fitted with an automatic identification system, for example based on bar codes or 98a electronic labels of the RFID (RadioFrequency IDdentification) type or of the IRC (InfraRed Communication) type, which allows via '' a corresponding reader 98b of the central unit to automatically determine the values of desired flow rate and the current of regulation and to calculate the time of the various phases of the cycle of sterilization. These electronic tags can be placed inside the enclosure and advantageously be fitted with sensors making it possible to control the sterilization cycle, in particular chemical measurement sensors for for example the measurement of humidity, ozone, pH, or the level of nitrogen dioxide.

FIGS. 5 and 5a illustrate an exemplary embodiment of a treatment enclosure more specifically adapted to the sterilization of an endoscope and provided with a single plasma production zone. This treatment chamber 120 is characterized by a particular geometry of the electrodes constituting the plasma production zone which also allows the in situ production of sterilizing chemical species. Indeed, with conventional sterilization techniques, the internal areas of objects can pose sterilization difficulties if the active ingredients have difficulty reaching them. The problem is particularly true for cavities or the interior of tubes, as for example in the case of endoscope channels. However, the sterilization method of the invention which can perfectly be applied to the sterilization of these cavities also makes it possible to simply solve this problem of access to these internal zones of objects of very elongated shape. The enclosure 120 is in the form of a hermetically sealed casing, the interior space of which (the sterilization zone proper) is arranged according to the shape of the object to be treated 122. Thus, in the 'illustrated example, the endoscope being folded flat in the enclosure, it is defined a single plasma production area 124 at the level of the head 126 of the endoscope. The carrier gas is brought to the housing of the central unit 60 by an external link 128 and is redistributed to the plasma production zone respectively by an internal pipe 130. The electrodes of this plasma production zone are connected by a link 132 to an external high voltage connector 134 in connection with a corresponding compatible connector 136 of the common central unit 60. A link 138 allows the evacuation to this central unit 60 of the gas after treatment. To ensure good sterilization of the internal surface of the endoscope channel 140, the sterilization zone is formed of a first zone 142 surrounding the head of the endoscope 126 and maintained at slight overpressure to ensure the desired flow rate at the inside the channel 140, the rest of the instrument being placed in a second zone 144 separated from the previous one by a passage 146 of determined diameter and which will allow the treatment of the external surface of the endoscope. This passage by creating an annular restriction around the endoscope keeps the first zone 142 slightly under pressure. In an alternative embodiment, it is possible to connect the end of the channel to a pump allowing a slight depression to be created in order to ensure the flow in the channel in order to use the same plasma source. Of course, non-return valves and / or anti-bacterial filters are provided at the interfaces of the housing 100 to ensure its tightness after its disconnection from the common central unit 60. Individual control of this housing is ensured by means of indication and control 92 placed on the central unit. The improved process thus described is both simple in design, since the enclosure does not need to resist differences in high pressure and the gas supply system is simplified and easy to use, since there are no chemicals to handle before and after the sterilization cycle and the risks of pollution are limited. In addition, the high voltage and low frequency power system has a simple structure and can be adapted to different configurations.

The proposed applications relate mainly to the medical field, but the process can be extended to many other industrial applications, for example in the food or pharmaceutical fields.

Claims

1. A method of sterilization by plasma in the presence of moisture (14) from a non-biocidal gas containing oxygen and nitrogen from at least one object (20) placed outside the discharge in a sealed treatment enclosure (10) subjected substantially to atmospheric pressure, characterized in that it comprises the following stages:

- introduction of the non-biocidal gas humidified in the treatment enclosure, - creation of a discharge of a first plasma A for a determined period making it possible to guarantee the effectiveness of sterilizing species created during the following phase as a whole of the enclosure,

- creation of a discharge of a second plasma B for a determined period allowing the sterilization of said object, - rinsing of the treatment chamber for a determined period so as to guarantee a non-polluting atmosphere during the subsequent opening of the 'pregnant.

2. A sterilization method according to claim 1, characterized in that said determined durations are further calculated as a function of the volume of the treatment enclosure.

3. A sterilization method according to claim 1, characterized in that the end of the rinsing step is detected by crossing a threshold measured by a multi-parameter sensor (46) placed at the outlet of the treatment enclosure.

4. A sterilization method according to claim 1, characterized in that the discharge of the first plasma and the introduction of moisture are simultaneous.

5. A sterilization method according to claim 1, characterized in that the discharges of the first and second plasmas use the same plasma source (12).

6. A sterilization method according to claim 5, characterized in that the discharges of the first and second plasmas are of different nature to allow separate optimization of each of the phases.

7. A sterilization process according to claim 1, characterized in that the flow rate of the non-biocidal gas is different between the different phases.

8. Sterilization method according to claim 1, characterized in that the choice of discharge regimes for the first and second plasmas is determined by the type of pattern of the voltage signal (sinusoidal, sinusoidal damped or continuous), the repetition frequency of the pattern and the total setpoint current.

9. A sterilization method according to claim 1, characterized in that the control of the discharge regime used is carried out by the detection of the peak current.

10. A sterilization method according to claim 9, characterized in that said detection is carried out with a bandwidth of the order of the frequency between the pulses.

11. A sterilization method according to claim 1, characterized in that the repetition frequency of the pattern or a latency time between the patterns is used to limit the rise in temperature at the level of the object to be sterilized while maintaining the same regime of discharge.

12. A sterilization method according to claim 1, characterized in that there is further provided a thermalization of an evaporative humidifier at a temperature slightly lower than that of the object to compensate for the rise in temperature due to the discharge .

13. A sterilization method according to claim 1, characterized in that there is further provided a control of the effectiveness of a vaporizer so as to compensate for the rise in temperature due to the discharge.

14. The sterilization method according to claim 1, characterized in that the high voltage supply is produced from a pulsed low voltage supply (102) supplying a transformer (100) used as a filter and as a voltage booster.

15. The sterilization method according to claim 14, characterized in that the control of the repetition of the low voltage pulses makes it possible to define the elementary pattern and to introduce an adjustable latency time.

16. Sterilization method according to claim 14, characterized in that the repetition frequency of the low voltage pulses is lower than the resonant frequency of the transformer.

17. Sterilization method according to claim 14, characterized in that the repetition frequency of the low voltage pulses is equal to the resonant frequency of the transformer.

18. A sterilization method according to claim 14, characterized in that the supply is regulated on the basis of a measurement of a current, preferably continuous for a continuous supply, synchronous for an alternative supply.

19. A sterilization method according to claim 18, characterized in that said current measurement is carried out through a resistor or by measuring the charge of a capacitor.

20. A sterilization method according to claim 19, characterized in that, in the case of a continuous supply, the discharge of the capacitor is ensured by periodic grounding.

21. Sterilization method according to claim 18, characterized in that the supply is regulated on the basis of a peak current measurement.

22. Sterilization method according to claim 21, characterized in that the signal used for regulation is smoothed with a time constant greater than 100 ms, preferably 1 s.

23. The sterilization method according to claim 1, characterized in that the electrodes are produced from a blade comprising one or more points parallel to a flat or cylindrical surface serving as counter-electrodes.

24. The sterilization method according to claim 23, characterized in that the number of tips is chosen so as to facilitate the use of the different discharge regimes desired during the treatment.

25. The sterilization method according to claim 1, characterized in that the discharges of the first and second plasmas overlap so that the creation of the second plasma B begins before that of the first plasma A ends.

26. A sterilization device comprising several treatment chambers, each treatment chamber comprising at least one plasma production zone connected in a fixed manner or not to at least one sterilization zone, the plasma production zones being connected to a common central unit containing at least the first non-biocidal gas source, the humidification chamber, the gas residue recovery system and the high-voltage power supply, device characterized in that the central unit comprises as many high-voltage power supplies than outputs allowing the speakers to be treated simultaneously by applying different discharge regimes.

27. A sterilization device according to claim 26, characterized in that the sterilization zone is slightly pressurized to allow flow into fine capillaries.

28. A sterilization device according to claim 26, characterized in that the common central unit comprises a multi-parameter sensor for each connection channel making it possible to control the composition of the gas leaving an enclosure before filtration.

29. A sterilization device according to claim 28, characterized in that said sensor makes it possible to measure the humidity and the ozone concentration.