A SYSTEM, A MACHINE, A PROCESS AND A METHOD IN THE MANUFACTURE OF PACKAGES

TECHNICAL FIELD The present invention relates to a system and a process for providing at least a flow of a sterilization agent to at least one sterilization unit in a filling machine. The present invention also relates to a filling machine including a system as above, and a method for the manufacture of packages comprising a process as above. The system includes at least one flow regulator for discharging the flow of sterilization agent, two containers for sterilization agent, the containers each being connected to the flow regulator and alternatingly catering for the supply of sterilization agent to the flow regulator, and a pressure regulator which is connected to each one of the containers and is supplied with an excess pressure in order to pressurise the containers.

BACKGROUND ART

Within the food industry, it is usual practice to pack drinks and other products in paper- or paperboard-based packages. Packages intended for liquid foods are often manufactured from a packaging laminate comprising a relatively strong core layer of paper or paperboard and an outer, liquid-tight layer of thermoplastic material on at least that side of the core layer which is to form the inside of the packages. For particularly oxygen-gas sensitive foods, such as juice and cooking oil, the packaging laminate also normally includes a layer of a gas barrier material. This layer is often in the form of an aluminium foil which, moreover, makes for induction sealing of the packaging laminate. Packages are often manufactured in a packing and filling machine where a web of packaging laminate is formed into a tube which is closed by sealing of the longitudinal edges of the web in an overlapping state. The tube sealed in the longitudinal direction is continuously filled with a product and subsequently transversely sealed, filled "cushions" being formed. The transverse sealing is made along narrow, transverse, mutually spaced apart sealing zones. After the transverse sealing, the "cushions" are separated from the rest of the tube by incisions in the sealing zones and are finally formed into the desired configuration.

Nowadays, so-called carton bottles are commonly occurring packages. These consist substantially of a lower portion in the form of a sleeve of packaging laminate like that described above, and an upper portion in the form of a plastic top provided with an opening device such as a screw cap. The carton bottles are often manufactured in a packing and filling machine where sheets, so-called "blanks" of packaging laminate are formed into tubes which are closed by sealing of two opposing edges in each sheet in an overlapping state. Each tube is thereafter passed over its respective plastic top and is disposed such that the greater part of the plastic top projects outside the tube. After sealing of the top and the tube along their mutual contact surface between them, there follows filling, sealing of the open end of the tube for forming a sleeve, and closing of the package, as well as final forming.

The above manufacturing methods are well-known in the art and will not be described in greater detail.

In order to extend the shelf-life of the packed product, it is known in the art to sterilize the packaging material before the filling operation and sometimes also the forming operation. Depending upon the desired length of shelf-life, and depending upon whether the packages are to be distributed and stored in a refrigerated environment or at room temperature, different levels of sterilization may be selected.

One prior art method in which packaging material may be sterilized is chemical sterilization. Chemical sterilization may, for example, be put into effect by causing the packaging material to pass through a bath containing liquid hydrogen peroxide and thereafter a heating station for removal of the hydrogen peroxide. This method functions excellently as regards the sterilization of a web of packaging laminate. However, the method is obviously less well suited for the sterilization of open carton bottles before filling. In that case, gas phase sterilization may instead be applied.

One sterilization apparatus for gas phase sterilization of carton bottles is described in Swedish Patent Specification 0203692-9, which is hereby incorporated herein as reference. The patent specification discloses how the carton bottles are sterilized in that, disposed upside down on a conveyor belt, they are caused to pass first through a heating zone, then a sterilization zone and finally a ventilation zone. In the sterilization zone, the carton bottles are exposed to gaseous hydrogen

peroxide. In order to prevent the hydrogen peroxide from condensing on the surface of the carton bottles in the sterilization zone, which impedes later removal, the carton bottles are heated up in the heating zone to a temperature above the dew point of the hydrogen peroxide gas. In the ventilation zone, the carton bottles are exposed to sterile hot air in order to ventilate off hydrogen peroxide which remains in and on the carton bottles.

In order for the sterilization to be sufficient, it is important that the carton bottles undergo a sufficiently powerful exposure to hydrogen peroxide. However, the exposure may not be so powerful that inadmissible residual quantities of hydrogen peroxide remain in and on the carton bottles when they leave the ventilation zone. For this reason, it is important to carefully monitor the supply of hydrogen peroxide gas to the sterilization zone in order to achieve the desired hydrogen peroxide gas concentration there.

One prior art packing and filling machine with a sterilization apparatus like that described above comprises two buffer tanks for liquid hydrogen peroxide. The buffer tanks are interconnected with a pressure regulator which is supplied with excess pressure in order to pressurise the buffer tanks at a constant predetermined pressure. The buffer tanks are further connected to a flow regulator for discharging a predetermined, substantially constant flow of hydrogen peroxide to an evaporator device in the packing and filling machine. In the evaporator device, the liquid hydrogen peroxide is vaporised and the resultant hydrogen peroxide gas is fed into the sterilization zone of the sterilization apparatus. Thus, it is the flow regulator which determines the concentration of hydrogen peroxide gas in the sterilization zone. In actual fact, the predetermined flow which is to be discharged from the flow regulator in order to achieve the desired concentration in the sterilization zone is extremely slight, which places severe demands on the flow regulator. On the market, there are flow regulators which are specially adapted for practical applications involving extremely slight flows. These function excellently as long as the pressure of the hydrogen peroxide which is fed from the buffer tanks is substantially constant or varies slowly. However, for reasons of space in the packing and filling machine, the buffer tanks have a relatively limited volume and the quantity of hydrogen peroxide in a full buffer tank stays only a relatively short time in normal operation of

the packing and filling machine. Normally, one buffer tank at a time is used for the supply of hydrogen peroxide to the flow regulator. When the first buffer tank is used and begins to empty, a switch must take place to the second buffer tank. After the switch, when the second buffer tank is employed for the supply of hydrogen peroxide to the flow regulator, the first buffer tank is replenished with hydrogen peroxide from a larger storage tank disposed outside the packing and filling machine.

In connection with a switching between the buffer tanks, there may occur rapid variations in the pressure of the hydrogen peroxide which is fed to the flow regulator. One reason for these rapid variations may be that air enters into the communication between the flow regulator and the buffer tanks during the switch. Another reason may be the acceleration of hydrogen peroxide from the "new" buffer tank in connection with the switching from the "old" buffer tank. Today's flow regulators have difficulty in handling such rapid variations in the pressure of the infed hydrogen peroxide. This implies that the flow out from the flow regulator in connection with a switching runs the risk of deviating from the predetermined, substantially constant hydrogen peroxide flow.

Fig. 1 is a diagram showing how the hydrogen peroxide flow which is discharged from the flow regulator may vary with time in connection with a switching between the buffer tanks in the prior art packing and filling machine. At time zero, the switching is initiated and the diagram shows the appearance of the flow (A) during 300 seconds after the switch. The bottom line (B) shows the constant pressurising by the pressure regulator of the buffer tanks and lines (C) and (D) demark the upper and lower tolerances, respectively, for the hydrogen peroxide flow. As is apparent from the diagram, the switching causes extreme variations in the hydrogen peroxide flow which is discharged from the flow regulator. After roughly 65 seconds, the peroxide flow even lies outside the tolerance line D. In due course, after roughly 215 seconds, the flow stabilises again about the desired, predetermined value.

A deviation in the flow out from the flow regulator entails a deviation from the desired concentration in the hydrogen peroxide gas concentration in the sterilization zone. This in turn may result in an insufficient sterilization of the carton bottles or in inadmissible residual quantities of hydrogen peroxide in and on the

carton bottles when these leave the ventilation zone. Carton bottles which have not correctly sterilized must be rejected. For this reason, the packing and filling machine is stopped when a sufficiently large deviation in the outward flow from the flow regulator is discovered. The term sufficiently large deviation is taken to signify here a deviation which results in a hydrogen peroxide flow outside the tolerance limits. The machine is not started again until the pressure of the hydrogen peroxide which is fed into the flow regulator has stabilised and the flow regulator once again discharges the predetermined flow. Those packages which have had time to be sterilized incorrectly before the machine is stopped must however be rejected, which naturally entails major economic losses. A machine stoppage also involves major economic losses. These problems may become particularly serious, since the switching between the buffer tanks must be made so often.

BRIEF SUMMARY OF THE INVENTION One object of the present invention is to realise a system, a filling machine comprising such a system, a process and a method for the manufacture of packages comprising such a process, for realising at least one flow of a sterilization agent to at least one sterilization unit in a packing and filling machine, which at least partly obviates any possible limitations which may be inherent in the prior art technique. The fundamental concept of the present invention is, at least in connection with a tank switch, to realise a possibility for actively monitoring and controlling the pressure regulator based on signals in respect of the current flow from the flow regulator, in order to reduce the variations in the pressure of the sterilization agent which is supplied to the flow regulator, and thereby the variations in the flow which is discharged out from the flow regulator.

The system, the packing and filling machine, the process and the method for realising the above object are defined in the appended Claims and will be discussed more closely below.

A system according to the present invention for providing at least one flow of a sterilization agent to at least one sterilization unit in a packing and filling machine comprises at least one flow regulator for discharge of the flow of sterilization agent, two containers for sterilization agent, each one of the containers being interconnected

with the flow regulator and alternatingly catering for the supply of sterilization agent to the flow regulator, and a pressure regulator which is connected to each one of the containers and supplied with excess pressure in order to pressurise the containers. The system is characterised in that it further includes a feedback device which is disposed, at predetermined intervals, to read off an actual value of the flow from the flow regulator, compare the actual value with each respective norm value and control the pressure regulator in accordance with the comparison between the actual value and the norm value.

If the packing and filling machine is of the type which was discussed by way of introduction in the section relating to background art, the sterilization unit includes the evaporator device and the sterilizer device, and the containers for sterilization agent relate to the buffer tanks.

The expression "alternatingly" is taken to signify that the sterilization agent which is discharged from the flow regulator first comes from the one, and then from the other of the containers, and so on. Precisely at the actual switch between the containers, the sterilization agent which is discharged from the flow regulator may derive from both of the containers.

The norm value, which after all is the desired value of the flow from the flow regulator, is normally constant over time, but the actual value which clearly is the true value of the flow from the flow regulator normally varies more or less over time, in particular in connection with a switching between the containers.

The pressure regulator is disposed to limit the excess pressure in a suitable manner in order to obtain a desired pressurisation of the containers. By controlling the pressure regulator based on actual, current values relating to the flow of sterilization agent from the flow regulator, the pressurisation of the containers can, if appropriate, be altered in order to reduce variations in the pressure of the sterilization agent which is fed to the flow regulator. By such means, the variations in the flow from the flow regulator will also be reduced, which entails a considerably reduced risk that the filling machine must be stopped and packages must be rejected. For example, a comparison between the actual value and the norm value can result in a quotient or a difference between the value in accordance with which the pressure regulator is controlled.

The controlling of the pressure regulator also implies an increase of the pressurisation of the containers if the outgoing flow from the flow regulator is too low and certain conditions are satisfied. Correspondingly, the control of the pressure regulator implies a reduction of the pressurisation of the containers if the outgoing flow from the flow regulator is too great and certain conditions are satisfied.

The feedback device may be disposed to control the pressure regulator so that a first increase of the pressurisation will be obtained if the difference between the actual value and the norm value is negative and has an absolute value which exceeds a first limit, the first increase being a function of the absolute value. The first limit value indicates how much the actual value may deviate from the norm value before the pressure regulator is controlled for increasing the pressurisation.

The first increase may, for example, be proportional to the absolute value of the difference between the actual value and the norm value. The feedback device may be disposed to control the pressure regulator so that a first reduction of the pressurisation is obtained if the difference between the actual value and the norm value is positive and has an absolute value which exceeds a second limit value, the first reduction being a function of the absolute value.

The second limit value, which may be but need not necessarily be equal to the first limit value, indicates how much the actual value may deviate from the norm value before the pressure regulator is controlled for reducing the pressurisation.

The first reduction may, for example, be proportional to the absolute value of the difference between the actual value and the norm value.

The feedback device may be disposed to control the pressure regulator so that a second increase of the pressurisation is obtained if the difference between the actual value and the norm value is negative and has an absolute value which exceeds a third limit value, and the actual value is decreasing, the second increase being a function of how rapidly the actual value is decreasing.

The third limit value, which may be but need not necessarily be equal to the first limit value, indicates how much the actual value may deviate from the norm value before the pressure regulator is controlled for increasing the pressurisation.

The expression "decreasing" is taken to signify that the actual value has a negative trend or derivate, i.e. the actual value at the pertinent read-off is less than the actual value at the preceding read-off. In one case where the current read-off is the first read-off, the actual value can "at the preceding read-off be set as equal to the norm value.

The second increase may, for example, be proportional to the absolute value of the difference between the actual value at the pertinent read-off and the actual value at the preceding read-off divided by δt, where δt = the time difference between the current read-off and the preceding read-off. The feedback device may be disposed to control the pressure regulator so that a second reduction of the pressurisation is obtained if the difference between the actual value and the norm value is positive and has an absolute value which exceeds a fourth limit value, and the actual value is increasing, the second reduction being a function of how rapidly the actual value is increasing. The fourth limit value, which may be but need not necessarily be equal to the first limit value, indicates how much the actual value may deviate from the norm value before the pressure regulator is controlled for reduction of the pressurisation.

The expression "increasing" is taken to signify that the actual value has a positive trend or derivate, i.e. that the actual value at the current read-off is greater than the actual value at the preceding read-off. In one case where the current read-off is the first read-off, the actual value "at the preceding read-off can be set equal to the norm value.

The second reduction may, for example, be proportional to the absolute value of the difference between the actual value at the current read-off and the actual value at the preceding read-off divided by δt, where δt = the time difference between the current read-off and the preceding read-off.

The feedback device may be disposed to control the pressure regulator so that a third increase of the pressurisation is obtained if the quotient between the actual value and the norm value is less than a fifth limit value which is less than one, the third increase implying that the pressurisation increases in compliance with a predetermined growth pattern independent of the quotient as long as the

pressurisation is less that a sixth limit value and the feedback device reads off an actual value which, on comparison with the respective norm value, gives a quotient which is less than a seventh limit value which is greater than the fifth limit value and less than one, that the pressurisation is thereafter held substantially constant until the feedback device reads off an actual value which, on comparison with the respective norm value, gives a quotient which is greater than the seventh limit value and that the pressurisation thereafter falls in compliance with a predetermined fall pattern independent of the quotient.

The above embodiment thus implies that the pressurisation grows at a predetermined rate until the pressurisation has reached a given sixth limit value or the quotient between the actual value and the norm value has increased and reached a given seventh limit value.

The fifth limit value discloses how much the actual value may deviate from the norm value before the pressure regulator is controlled so as to permit the pressurisation to increase. Correspondingly, the seventh limit value discloses how much the actual value may deviate from the norm value before the pressure regulator is controlled in order to allow the pressurisation to fall. The sixth limit value discloses in its turn how great the pressurisation may be during the third increase.

The fifth limit value may, but need not necessarily be equal to the first limit value.

The increase pattern and the fall pattern may be produced experimentally in accordance with the specific preconditions for the system according to the present invention. For example, the third increase may be in the form of a parallelogram which lacks a base, i.e. one of the parallel sides. In accordance therewith, the system may be constructed such that the pressurisation, on the third increase, grows from a start value in order subsequently to fall back to the start value.

Naturally, the above different embodiments of the feedback device may be combined in any manner whatever within one and the same embodiment. According to one embodiment, the feedback device may be disposed to control the regulator so that a first, a second and a third increase of the pressurisation will be obtained if each of the above respective conditions are satisfied. The resultant total increase of the pressurisation may then be the sum total of the first, second and third increases.

According to the same embodiment, the feedback device may be disposed to control the regulator so that a first and a second pressure reduction are obtained if each of the above respective conditions are satisfied. The resultant total reduction of the pressurisation may then be the sum total of the first and the second reductions. It follows from the foregoing that the qualifications first up to and including seventh in front of the words increase, reduction and limit value have nothing to do with sequence but are merely employed for distinguishing purposes.

According to one embodiment, the feedback device is disposed to be active only during a switch between the containers and a predetermined time after the switch. As was described by way of introduction, it is precisely in connection with a switching between the containers that the feedback function is needed most in order to minimise variations in the outgoing flow from the system. After the predetermined time, it is expected that the system will have stabilised and the feedback device may then be deactivated until it is time for the next switch. The system according to the present invention may be constructed in such a manner that the one container is disposed to be filled with sterilization agent when the second container caters for the supply of sterilization agent to the flow regulator. The advantage inherent in such a construction is that the system can be driven continuously and need not be stopped for replenishment of sterilization agent. According to one embodiment, the system includes two flow regulators each for discharging a flow of sterilization agent, the flow regulators each being interconnected with the containers for sterilization agent. In this embodiment, the feedback device is disposed to read off the actual values of the flows from the flow regulators, compare the actual values with each respective norm value for obtaining each respective difference and controlling the pressure regulator in response to the comparison which corresponds to the difference with the greatest absolute value.

The above embodiment makes for the provision of a flow of sterilization agent to each one of two sterilization units in a filling machine which, thereby, may have two production lines for producing twice as many packages. The production lines could be identical and thereby require the same flow of sterilization agent, or be different and consequently require different flows.

The sterilization agent which is used in the system may, for example, be liquid hydrogen peroxide which is a thoroughly well tested and effective sterilization agent within the packaging industry.

A filling machine according to the present invention includes a system as described above.

A process according to the present invention for realising at least one flow of a sterilization agent to at least one sterilization unit in a filling machine comprises discharging the flow of sterilization agent through at least one flow regulator, supplying sterilization agent to the flow regulator alternatingly from two containers for sterilization agent, each one of which containers being interconnected with the flow regulator, and pressurising the containers by supplying a pressure regulator with excess pressure, the pressure regulator being interconnected with each one of the containers. The process is characterised in that it further includes, with predetermined intervals through a feedback device, reading off an actual value of the flow from the flow regulator, comparing the actual value with each respective norm value and controlling the pressure regulator in accordance with the comparison between the actual value and the norm value.

A method according to the present invention for manufacturing packages includes the process as disclosed above. Those characterising features which were discussed in connection with the system according to the present invention for realising at least one flow of a sterilization agent to at least one sterilization unit in a filling machine are naturally transferable to the corresponding filling machine according to the present invention, and the method for manufacturing packages and the corresponding process according to the present invention. Moreover, these characterising features may naturally be combined in one and the same embodiment.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

The present invention will now be described in greater detail hereinbelow, with reference to the accompanying schematic Drawings which show examples of currently non-restrictive preferred embodiments of the present invention. In the accompanying Drawings:

Fig. 1 is a diagram which illustrates the flow from a flow regulator in a filling machine according to the prior art technology;

Fig. 2 is a schematic sketch illustrating a system according to the present invention; Fig. 3 is a flow diagram which illustrates a process according to a first embodiment of the present invention;

Fig. 4 is a diagram which illustrates the flows from the flow regulators in the system according to Fig. 1 according to the first embodiment;

Fig. 5 is a flow diagram which illustrates a part of a process according to a second embodiment of the present invention; and

Fig. 6 is a diagram which illustrates the flows from the flow regulators in the system according to Fig. 1 according to the second embodiment.

DESCRIPTION OF PREFERRED EMBODIMENTS Fig. 2 schematically shows a system 10 according to the present invention.

The system is included in a filling machine (not shown in its entirety) for the manufacture of carton bottles as described above in the section relating to background art. The filling machine has two production lines and, in accordance therewith, the purpose of the system 10 is to provide respective flows of liquid hydrogen peroxide to each one of two sterilization units which are also included in the filling machine. The two production lines are intended for the manufacture of identical packages and, as a result, the flows which are provided by the system must be kept as alike as possible. Each one of the sterilization units includes an evaporator device for vaporising the liquid hydrogen peroxide. The evaporator devices are shown in Fig. 2 and are there designated by means of reference numerals 12 and 14. The resulting hydrogen peroxide gas is fed to a sterilization zone (not shown) in the machine which is also included in each one of the sterilization units. When the carton bottles pass the sterilization zone, they are exposed to the hydrogen peroxide gas as one phase in the sterilization process. Since sterilization by such means is previously known in the art and moreover described in the patent specification to which reference is made above, no more detailed description will be provided here.

The system 10 includes two identical buffer tanks 16 and 18 for liquid hydrogen peroxide and an electronically controllable pressure regulator 20. The buffer tanks are disposed alternatingly to cater for the provision of hydrogen peroxide to the sterilization units. The pressure regulator is fed with an excess pressure P of 6 bar and is further, by means of conduits, connected to each one of the buffer tanks 16 and 18 for pressurising them. The pressure regulator is pre-set, during stable operation of the filling machine, to pressurise the buffer tanks with 1.8 bar. Valve means 22 and 24 are disposed on the conduits between each one of the buffer tanks 16 and 18 and the pressure regulator 20 in order to regulate the pressurisation of the buffer tanks. In addition, each one of the buffer tanks is, by means of conduits, in double communication with a bleeder tank 26. Valve means 28 and 30; and 32 and 34, respectively are disposed on the conduits between each one of the buffer tanks and the bleeder tank in order to regulate bleeding of the buffer tanks. Further valve means 36 for regulation of the bleeding operation is moreover disposed between the valve means 32 and 34 and the bleeder tank 26.

The buffer tanks 16 and 18 are each further, by means of conduits, connected to two flow regulators 38 and 40 which in turn, by means of additional conduits and respective valve means 42 and 44, are connected to each one of the evaporator devices 12 and 14 of the sterilization units. The flow regulators 38 and 40, which are marketed by Bronkhorst High-Tech BV, the Netherlands, under the name LIQUI- FLOW ^® , are particularly adapted for practical applications where it is desirable to discharge extremely slight quantities of liquid with a high degree of accuracy. In connection with the system 10, the flow of hydrogen peroxide which is desired out from each one of the flow regulators is 4.2 kg/h, i.e. relatively slight. With this flow, there will be obtained a concentration of hydrogen peroxide gas in the sterilization zones which is sufficient to attain a desired level of extermination without being so great that there is a risk of inadmissible residual quantities of hydrogen peroxide in and on the carton bottles after completed sterilization. Large variations from the desired value of the hydrogen peroxide flows discharged out from the flow regulators may result in incorrect sterilization of the carton bottles.

For reasons of space, the buffer tanks 16 and 18 have a relatively limited volume and the hydrogen peroxide which is accommodated in one of the buffer

tanks, for example buffer tank 18, when this is filled to a given maximum level, is only sufficient for discharging the desired flow from the flow regulators 38 and 40 during a relatively short time. After roughly eight minutes, the hydrogen peroxide level in the buffer tank 18 has fallen to a given minimum level and then it is time to switch over to the buffer tank 16. While using the buffer tank 16, the buffer tank 18 is replenished, and so on, as will be described below. By such means, it will be ensured that there is always hydrogen peroxide available for the flow regulators 38 and 40. For monitoring the hydrogen peroxide level in the buffer tanks, a sensor device 46 and 48 for detecting the maximum level and a sensor device 50 and 52 for detecting the minimum level are provided in each one of the buffer tanks 16 and 18.

By conduits, the buffer tanks 16 and 18 are connected to two identical storage tanks 54 and 56 for liquid hydrogen peroxide. While this is not apparent from the figures, the storage tanks have a volume which is considerably greater than the volume of the buffer tanks. The storage tanks are arranged to cater one at a time for replenishing the buffer tanks with hydrogen peroxide. When the hydrogen peroxide in one of the storage tanks, for example storage tank 56, is consumed, a switch is made to storage tank 54. While storage tank 54 is being used, storage tank 56 may be replaced or alternatively replenished. By such means, it will be ensured that hydrogen peroxide is always available for the buffer tanks 16 and 18 and thereby the flow regulators 38 and 40. Valve means 58, 60, 62 and 64 are disposed on the conduits in order to regulate the replenishment of hydrogen peroxide from the storage tanks to the buffer tanks. Further, a pump 66 is provided between the valve means 58, 60 and the valve means 62, 64 for carrying out the actual transfer of hydrogen peroxide from the storage tanks to the buffer tanks. As was mentioned above, large variations from the desired value of the hydrogen peroxide flows discharged out from the flow regulators 38 and 40 may result in incorrect sterilization of the carton bottles which are manufactured in the filling machine. As a result, but slight variations in the flows are permitted in the system 10 in order to ensure that sterilization takes place in the correct manner. If the flows from the flow regulators fall outside 4.2 kg/h ± 12 %, the deviation from the desired flow value is assessed as being excessive. As was described by way of

introduction, this results in the filling machine being stopped and carton bottles needing to be rejected, with major economic losses as a result.

When the pressure of the hydrogen peroxide which is fed to the flow regulators from the buffer tanks 16 and 18 is constant or changes relatively slowly, the flow regulators function satisfactorily and they each discharge a substantially constant flow of 4.2 kg/h. However, if the pressure of the hydrogen peroxide which is fed to the flow regulators varies relatively rapidly, the flow regulators may find difficulty in keeping each respective discharged flow constant and a risk of incorrect sterilization of the carton bottles may thereby occur. Such rapid pressure variations are particularly common in connection with switching between the buffer tanks 16 and 18. One reason for these rapid variations may be that, during the switch, air bubbles occur in the conduits between the flow regulators and the buffer tanks. Another reason may be the acceleration of the hydrogen peroxide from the "new" buffer tank on switching from the "old" buffer tank. For purposes of clarity, a list is given below of the steps involved in a switch from buffer tank 18 to buffer tank 16:

• Close valve means 28

• Pressurise buffer tank 16

• Wait until the pressure is stable in buffer tank 16 • Open valve means 32

• Close valve means 34

• Close valve means 24

• Open valve means 30

• Open valve means 60 • Start pump 66

• Wait until the peroxide level in the buffer tank 18 is equal to the maximum level

• Close valve means 60

Otherwise, discussions of system components which make no contribution to the inventive concept proper will be omitted.

In order to reduce the variations in the hydrogen peroxide flows discharged out from the flow regulators, and thereby reduce the risk of deviations from the desired flow value which are excessive, the system includes a feedback device 68 which is disposed to communicate with the flow regulators 38 and 40 as well as the flow regulator 20 and operates in accordance with the flow diagram which is shown in Fig. 3. The feedback device 68 is disposed, during 100 seconds from a switch between the buffer tanks 16 and 18, to read off (step A) an actual value of the flow from each one of the flow regulators 38 and 40. This read-off is carried out at predetermined intervals, with spaces of 40 ms, and after each read-off differences (step B) are calculated between the actual values and each respective norm value. As is apparent from the foregoing, the norm values here are constant and equal to 4.2 kg/h. The feedback device is thereafter disposed to compare (step C) the absolute value of the differences in order to control the pressure regulator in accordance with the actual value which deviates most from the norm value. If the flows of hydrogen peroxide out from the flow regulators 38 and 40 are too small, the feedback device is disposed to temporarily control the pressure regulator 20 to increase the pressurisation of the buffer tanks 16 and 18 in order to increase the flows. In accordance herewith, according to a first embodiment of the invention, the feedback device is disposed to examine (step D) whether the quotient between the most deviating actual value and the norm value is less than a (fifth) limit value = 0.97. If such is the case, the feedback device is further disposed to examine (step E) whether there is space available to increase the pressurisation of the buffer tanks, i.e. if the pressurisation is less than a (sixth) limit value = 2.3 bar. If the pressurisation can be increased, this is put into effect (step F) at a rate of 0.025 bar/s, and a status flag is set = controlling to mark that a (third) increase of the pressurisation has been initiated. If, on the other hand, the buffer tanks cannot be pressurised further (step E), the current setting of the pressure regulator 20 is maintained.

In the event it is instead (in step D) ascertained that the quotient between the most deviating actual value and the norm value is greater than, or equal to, 0.97, the feedback device is further disposed to examine (step G) whether the quotient is less than a (seventh) limit value = 0.98. If such is the case, the feedback device examines

(step H) further whether a (third) increase of the pressurisation has been initiated, i.e. if the status flag = control. In the event a (third) pressurisation increase has been initiated and there is (step I) space to increase the pressurisation, this is put into effect (step J) at a rate of 0.025 bar/s. If, on the other hand, no (third) increase has been initiated (step H), or if the buffer tanks cannot be pressurised further (step I), the current setting of the pressure regulator 20 is maintained.

If ₅ instead, it is ascertained (in step G) that the quotient between the most deviating actual value and the norm value is greater than, or equal to, 0.98, the feedback device is further disposed to examine (step K) whether a (third) increase of the pressurisation has been initiated, i.e. if the status flag = control. In the event that a (third) pressurisation has been initiated and the pressurisation of the buffer tanks is greater (step L) than the pre-set value = 1.8 bar, the pressurisation is reduced (step M) at a rate of 0.025 bar/s. If, on the other hand, no (third) increase has been initiated (step K), or if the pressurisation of the buffer tanks is not greater than 1.8 bar (step L), the current setting of the pressure regulator 20 is maintained. In this latter case, the status flag is also set (step N) = no control in order to mark that (the third) increase of the pressurisation has been completed.

Fig. 4 is a diagram which illustrates the above process and its effects on the flows of hydrogen peroxide discharged out from the flow regulators 38, 40 in connection with a switching between the buffer tanks 16, 18. At time zero, the switch is initiated and the diagram shows the appearance of the flows (α _1? βi) during 300 seconds after the switch. The lowermost curve (μi) shows the pressurisation of the buffer tanks by the pressure regulator and lines (ε) and (θ) mark the upward and downward tolerances, respectively, for the hydrogen peroxide flow, 4.2 kg/h ± 12 %. As is apparent from the diagram, the switching causes variations in the hydrogen peroxide flows which are discharged out from the flow regulators. As a response to these variations, the feedback device controls the pressure regulator so that the pressurisation of the buffer tanks is changed, as is apparent from the figure. This control implies that a (third) increase of the pressurisation is initiated when the quotient between the actual value for one of the flow regulators and the norm value becomes less than 0.97. The pressurisation then grows at a rate of 0.025 bar/s, which

results in the flows discharged out from the flow regulators beginning to grow as well. The pressurisation grows until the maximum pressurisation of the buffer tanks of 2.3 bar is achieved or the quotient between the actual value and the norm value has risen to 0.98. As is apparent from Fig. 4, the first of the alternatives occurs first in this example. When the pressurisation reaches 2.3 bar, the pressurisation is held constant until the quotient between the actual value and the norm value reaches 0.98. Thereafter, the pressurisation begins to fall back towards the pre-set value of 1.8 bar at a rate of 0.025 bar/s.

Because the feedback device controls the pressure regulator in the above- outlined manner, the flow variations in connection with tank switching are greatly reduced. As is apparent from Fig. 4, the control of the pressurisation entails that the hydrogen peroxide flows from the flow regulators never falls outside the tolerance lines (ε) and (θ).

In the above embodiment, the feedback device 68 is disposed to temporarily control the pressure regulator 20 to increase the pressurisation of the buffer tanks 16 and 18 if the flows of hydrogen peroxide out from the flow regulators 38 and 40 are too slight. The feedback device may further be disposed to temporarily control the pressure regulator 20 to reduce the pressurisation of the buffer tanks 16 and 18 is the flows of hydrogen peroxide out from the flow regulators 38 and 40 are too great. In accordance herewith, according to a second, more sophisticated, embodiment of the present invention, the feedback device is disposed to operate in accordance with the flow diagram which is illustrated in Fig. 3 and Fig. 5. According to the second embodiment, the feedback device operates according to the flow diagram which is shown in Fig. 3 and is described above. Thereafter, the feedback device operates in accordance with the flow diagram shown in Fig. 5. The total procedure is repeated during 100 s after a switching between the buffer tanks with an interval of 40 ms.

As is illustrated in Fig. 5, the feedback device is thus further (after steps A-N) disposed to examine (step O) whether the most deviating actual value is less than the norm value, i.e. if the difference between the most deviating actual value and the norm value is negative and has an absolute value which exceeds a (first = third) limit value = 0. If such is the case, the pressurisation is increased (step P) by ki * (the norm value - the most deviating actual value), where kj is a constant = 0.4.

(The first) increase is thus proportional to the absolute difference between the most deviating actual value and the norm value. The feedback device is thereafter disposed to examine (step Q) whether the most deviating actual value, i.e. the current actual value, is less than the preceding corresponding actual value, i.e. if the actual value is decreasing. The expression "corresponding" is taken to signify that there are always two actual values from the same flow regulator which are compared in this step. If this is correct, the pressurisation is increased (step R) by k ₂ * (preceding actual value — current actual value)/δt, where k ₂ is a constant = 0.1 and δt = the time between the read-offs of the current actual value and the preceding actual value. (The second) is thus proportional to the direction coefficient of the actual value.

In the case where instead (in step O) it is established that the most deviating actual value is not less than the norm value, the feedback device is disposed to examine (step S) whether the actual value is greater than the norm value, i.e. if the difference between the most deviating actual value and the norm value is positive and has an absolute value which exceeds a (second = fourth) limit value = 0. If such is the case, the pressurisation is reduced (step T) by ki * (the most deviating actual value - the norm value), where k _\ is a constant = 0.4. (The first) reduction is thus proportional to the absolute difference between the norm value and the most deviating actual value. The feedback device is thereafter disposed to examine (step U) whether the most deviating actual value, i.e. the current actual value, is greater than the preceding corresponding actual value, i.e. if the actual value is increasing. The expression "corresponding" is taken to signify, exactly as above, that there are always two actual values from the same flow regulator which are compared in this step. If this is correct, the pressurisation is reduced (step V) by k ₂ * (current actual value - preceding actual value)/ δt, where k ₂ is a constant = 0.1 and δt = the time between the read-offs of the current actual value and the preceding actual value. (The second) reduction is thus proportional to the direction coefficient of the actual value.

Fig 6 is a diagram which illustrates the above procedure and its effects on the flows of hydrogen peroxide discharged out from the flow regulators 38, 40 in connection with a switching between the buffer tanks 16, 18. At time zero, the switch is initiated and the diagram shows the appearance of the flows (α ₂ , β ₂ ) during

300 seconds after the switch. The lowermost curve (μ ₂ ) shows the pressurisation of the buffer tanks by the pressure regulator and the lines (ε) and (θ) mark the upward and downward tolerances, respectively, for the hydrogen peroxide flow, 4.2 kg/h ± 12 %. As is apparent from the diagram, the switch causes variations in the hydrogen peroxide flows which are discharged out from the flow regulators. As a response to these variations, the feedback device controls the pressure regulator so that the pressurisation of the buffer tanks is changed as is apparent from the figure. The control implies that a (first) increase of the pressurisation from the pre-set value of 1.8 bar is obtained as soon as the actual value of one of the flow regulators becomes less than the norm value, that a (second) increase is obtained when the actual value is less than the norm value and reducing and that a (third) increase is initiated when the quotient between the actual value and the norm value becomes less than 0.97. The increase of the pressurisation results, as is apparent from the figure, in the flows which are discharged out from the flow regulators increasing. The control further implies that a (first) reduction of the pressurisation from the pre-set value of 1.8 bar is obtained as soon as the actual value of one of the flow regulators becomes greater than the norm value and that a (second) reduction is obtained when the actual value is greater than the norm value and increasing. The reduction of the pressurisation results, as is apparent from the figure, in the flows which are discharged out from the flow regulators falling.

Because the feedback device controls the pressure regulator in the above manner, the flow variations in connection with the switch are greatly reduced. As is apparent from Fig. 6, the control of the pressurisation entails that the hydrogen peroxide flows from the flow regulators never fall outside the tolerance lines (ε) and (θ). A comparison between the diagrams in Figs. 4 and 6 further shows that the second embodiment of the present invention gives considerably smaller variations in the hydrogen peroxide flows from the flow regulators than the first embodiment.

As is apparent from the foregoing description, an increase of the pressurisation can thus be a result of, at most, three partial increases (first, second and third increase). Correspondingly, a reduction of the pressurisation can be a result of, at most, two partial reductions (first and second reduction). It should be observed

that the partial increases, exactly like the partial reductions, take place simultaneously even if this is not apparent from the flow diagrams.

During continuous operation of the filling machine, regular switches thus take place between the buffer tanks in order to ensure continuous supply of hydrogen peroxide to the flow regulators. In connection with each switching, the feedback device is activated which then, during 100 s, at intervals of 40 ms, repeats the flow diagram which is shown in Fig. 3 or Fig. 3 and 5, depending upon which embodiment of the present invention is applied. After 100 s, the system is deemed to have stabilised itself sufficiently after the switch and the feedback device then once again becomes inactive. The present invention entails that the temporary variations in the flow from the flow regulators which occur in connection with the switching will not be so great that the filling machine must be stopped and packages be rejected. Naturally, this involves enormous economic and practical advantages.

The above described embodiments should merely be considered as examples. A person skilled in the art will readily perceive that these embodiments may be modified and varied in a number of different ways without departing from the inventive concept as herein disclosed.

For example, the filling machine may naturally be disposed for producing other types of packages than carton bottles. The present invention may be applied in all situations where packaging material/packages can be sterilized with the aid of a sterilization agent in the gas phase. Thus, the present invention may advantageously be employed in connection with a filling machine like the filling machine described by way of introduction where packages are manufactured by continuous forming, filling and sealing of a tube of packaging laminate. In addition, the filling machine may be disposed for production of different types of packages, for example one type per production line. In such an event, the norm values for the two flow regulators can differ. Moreover, the norm values need not be constant over time.

Naturally, the filling machine may include more than two buffer tanks and more than two production lines and thereby flow regulators. The above configuration constitutes merely one example.

Finally, it should be observed that all figures are not drawn to scale and that all parameter values are merely examples and can thereby be varied.