Title of Invention	APPARATUS AND METHOD FOR STERILIZATION
Abstract	An apparatus (10) and a method for sterilization of a web (12) of packaging material are provided. The apparatus comprises a bath (20) through which the web is to be passed and a transfer system for transferring sterilization fluid from a supply (30) of sterilization fluid to the bath. The apparatus is characterized in that the transfer system comprises a buffer tank (18) to which sterilization fluid is transferred from the supply and a movable volume regulating element (34) for transferring sterilization fluid from the buffer tank to the bath. At least a part (36) of the volume regulating element is arranged to be received in the buffer tank and act upon the sterilization fluid therein, a volume of sterilization fluid in the bath thereby being a function of a position of the volume regulating element in the buffer tank. To be published with figure 2

Title of Invention

APPARATUS AND METHOD FOR STERILIZATION

Abstract

An apparatus (10) and a method for sterilization of a web (12) of packaging material are provided. The apparatus comprises a bath (20) through which the web is to be passed and a transfer system for transferring sterilization fluid from a supply (30) of sterilization fluid to the bath. The apparatus is characterized in that the transfer system comprises a buffer tank (18) to which sterilization fluid is transferred from the supply and a movable volume regulating element (34) for transferring sterilization fluid from the buffer tank to the bath. At least a part (36) of the volume regulating element is arranged to be received in the buffer tank and act upon the sterilization fluid therein, a volume of sterilization fluid in the bath thereby being a function of a position of the volume regulating element in the buffer tank. To be published with figure 2

Full Text	APPARATUS AND METHOD FOR STERILIZATION TECHNICAL FIELD OF THE INVENTION The present invention relates to an apparatus for sterilization of a web of packaging material, comprising a bath through which the web is to be passed and a transfer system for transferring sterilization fluid from a supply of sterilization fluid to the bath. The invention also relates to a method for sterilization of a web of packaging material, comprising transferring sterilization fluid from a supply of sterilization fluid to a bath and passing the web through the bath. BACKGROUND ART Within packaging technology, use has long been made of packages for packing and transporting beverages such as milk and juice but also other pourable products. A large group of these packages is produced from a laminated packaging material comprising a core layer of, for example, paper or paperboard and an outer, liquid-tight coating of thermoplastic material on at least that side of the core layer which forms the inside of the package. Sometimes the material also includes a gas barrier, for example in the form of an aluminum layer. Such packaging containers are often produced in that a web of packaging material is formed into a tube by sealing the longitudinal edges of the web in an overlapping condition. The longitudinally sealed tube is continuously filled with a product and then transversally sealed and formed into cushions. The sealing is made along narrow, transverse, mutually spaced apart, sealing zones. The transverse sealing of the tube takes place in a per se known manner substantially at right angles to the longitudinal direction of the tube and constantly in the same plane. The sealed-off portions of the tube thus containing contents are thereafter separated from the tube by means of incisions in these sealing zones and formed into the desired shape. This technology of forming a tube from a web is well known per se and will not be described in detail. To extend the shelf-life of the products being packed, it is prior known to sterilize the web before the filling operation and sometimes also the forming operation. Depending on the desired length of the shelf-life and whether the packages should be distributed and stored in a chilled or an ambient environment, different levels of sterilization can be chosen. One way of sterilizing a web of packaging material is chemical sterilization. In known machines for producing packages in the above described way, the web of packaging material is often chemically sterilized by being passed through a bath of hydrogen peroxide. For various reasons, an operator of such a machine sometimes needs to stop the machine operation, and thereby the web feeding, for shorter or longer periods of time. If the packaging material is of the initially described kind, i.e. a laminate with a core layer of paper covered on both sides with a liquid-tight coating of thermoplastic material, such stops could entail a risk of hydrogen peroxide being soaked into the paper core layer of the packaging material at the edges of the portion of the web that is immerged in the bath. One problem with such edge soaking of hydrogen peroxide is that it could lead to problems in connection with subsequent sealing. In connection with machine stops, the hydrogen peroxide may therefore be taken out of the bath and back into the supply container from where it was initially brought. However, in this way, unused hydrogen peroxide in the supply container is mixed with the used hydrogen peroxide from the bath. This is somewhat undesirable since the used hydrogen peroxide may be contaminated with e.g. paper dust from the packaging material. Further, the used hydrogen peroxide may be degraded, thereby having a lower concentration compared to the unused hydrogen peroxide. For this reason, this emptying of the bath is normally done only in connection with longer stops in order to avoid unnecessary mixing of new and used hydrogen peroxide. Thus, in connection with short stops, hydrogen peroxide is still present in the bath involving a risk of edge soaking in a portion of the web. Pumps are traditionally used for transferring the hydrogen peroxide between the supply container and the bath. Such pumps comprise a large number of moving parts, making them relatively complex. Further, since such pumps have a large number of wear details, their lives are relatively limited. SUMMARY OF THE INVENTION An object of the present invention is to provide an apparatus and a method for sterilization of a web of packaging material, which apparatus and method, at least partly, eliminate potential limitations of prior art. A basic concept of the invention is to provide a possibility for a supply of sterilization fluid to communicate indirectly with a bath through a buffer tank. Thereby, if the bath is to be emptied, used sterilization fluid can be returned to the buffer tank instead of the supply. Another basic concept of the invention is to provide a reliable, robust and durable element for transferring sterilization fluid from the buffer tank to the bath. The apparatus and method for achieving the objective above are defined in the appended claims and discussed below. An apparatus for sterilization of a web of packaging material according to the present invention comprises a bath through which the web is to be passed and a transfer system for transferring sterilization fluid from a supply of steriliza- tion fluid to the bath. The apparatus is characterized in that the transfer system comprises a buffer tank to which sterilization fluid is transferred from the supply and a movable volume regulating element for transferring sterilization fluid from the buffer tank to the bath. At least a part of the volume regulating element is arranged to be received in the buffer tank and act upon the sterilization fluid therein, a volume of sterilization fluid in the bath thereby being a function of a position of the volume regulating element in the buffer tank. The buffer tank makes it possible to empty the bath without mixing used and unused sterilization fluid. Therefore, the bath can advantageously be emptied in connection with all machine stops, long ones all well as short ones. By bath is meant a space that can be empty or filled and normally is limited by walls. Thus, with a vessel taken as an example, the bath is the interior of the vessel. Unless the supply is starting to go dry, it normally contains a relatively large volume of sterilization fluid compared to the volume of sterilization fluid needed to fill the bath to a sufficient level for sterilization of the web. In connection with apparatus start up, when the buffer tank and the bath is empty, sterilization fluid needs to be transferred from the supply to the buffer tank. After that, by means of the volume regulating element, at least some of the sterilization fluid should be transferred from the buffer tank to the bath. The fluid volume that needs to be transferred from the supply to the buffer tank is dependent on the construction of the volume regulating element. In an optimal case, where the volume regulating element is capable of transferring essentially all of the sterilization fluid from the buffer tank to the bath, the fluid volume that needs to be transferred from the supply to the buffer tank is essentially equal to the volume of sterilization fluid in the bath when this is filled to the sufficient level for sterilization. Hereby, the sterilization fluid can be used a particularly beneficial way. The volume regulating element is arranged to act on the sterilization fluid in the buffer tank to transfer at least a part of the fluid to the bath. This is done by some kind of movement of the volume regulating element in the bath, such as a lateral movement, rotational movement or a combination of these. By providing the apparatus with a volume regulating element working like this, instead of a traditional pump, the level of sterilization fluid in the bath can be controlled in a very neat way. Additionally, since the volume of sterilization fluid in the bath is a function of the position of the volume regulating element in the buffer tank, the speed by which the bath can be filled/emptied with/of sterilization fluid is dependent on the speed of the movement of the volume regulating element in the buffer tank. Thus, the faster movement of the volume regulating element in the bath, the faster filling/emptying of the bath can be obtained. In accordance with one embodiment, the apparatus can be constructed so that the volume of sterilization fluid in the bath increases when a distance between said part of the volume regulating element and a bottom wall of the buffer tank decreases. Here, the volume regulating element is arranged for lateral movement to push the sterilization fluid out of its way and directly or indirectly into the bath. This embodiment enables a relatively mechanically simple construction of the volume regulating element. According to one embodiment, said part of the volume regulating element is arranged to force the sterilization fluid in a direction opposite a moving direction of said part of the volume regulating element in the buffer tank. This could, as an example, mean that the fluid is pressed upwards and around the volume regulating element when the volume regulating element is moving downwards. Such a construction is beneficial since no extra means may be needed for bringing the fluid forced aside by the volume regulating element to the bath, the fluid instead being guided between the volume regulating element and the side wall(s) of the buffer tank. The inventive apparatus could be constructed in such a way that a side wall of the buffer tank is directly connected to a bottom wall of the bath. Further, it could be constructed with an edge of said side wall of the buffer tank being directly connected to an edge of said bottom wall of the bath. The last configuration means a direct transition from the buffer tank to the bath, wherein sterilization fluid forced out of the buffer tank by means of the volume regulating element automatically ends up in the bath. According to one embodiment of the inventive apparatus, the bath is arranged at a higher level than the buffer tank. This means that sterilization fluid in the bath can be drained to the buffer tank by gravity. This embodiment is beneficial since additional means, such as pumps, may not be needed for draining the bath. The apparatus can, in accordance with one embodiment, be constructed so that the volume regulating element is arranged to form at least a part of a side wall of the bath. Such a construction enables a particularly smart design of the apparatus as regards convenient limitation of the bath, rapid filling and emptying of the same, as well as good thrift of sterilization fluid. As described above, the bath of known packaging machines is emptied in connection with longer machine stops in order to avoid edge soaking into the web. The emptying is performed by means of a pump. However, if a machine stop is caused by a power failure, it is not possible to empty the bath since electricity is required for the pump to work. Thus, in connection with not only short stops but also power failures, sterilization fluid is still present in the bath of known machines. This involves a risk of edge soaking in a portion of the web. Also, if there should be a need for the operator to access the machine in the area of the bath during a short stop or a power failure, e.g. because of repairs or maintenance, he/she could be subjected to a risk of unhealthy exposure to sterilization fluid. However, in accordance with one embodiment of the present invention, the volume regulating element is arranged to take a default position in connection with an apparatus stop, sterilization fluid thereby automatically being drained from the bath to the buffer tank. This property makes emptying of the bath very fast and easy, even in connection with apparatus stops in the form of power failures. Thus, in connection with an apparatus stop, the bath is automatically drained, whereby edge soaking into the web of packaging material is prevented. The bath need not be completely drained to achieve this result, but only to a level beneath the material web. However, to ensure that an operator, who is accessing the area of the bath in connection with the apparatus stop, is not exposed to the sterilization fluid, the bath should be completely drained. By apparatus stop is meant a condition where the web of packaging material is kept still in the bath. To promote the arrangement of the volume regulating element in the default position in connection with an apparatus stop, the volume regulating element can be spring-loaded so as to strive towards this position in connection with a stop. According to one embodiment, the volume regulating element is arranged to at least partly cover a surface of the sterilization fluid in the buffer tank in the default position. This embodiment is advantageous since the volume regulating element thereby will help prevent an operator accessing the apparatus from being exposed to the sterilization fluid in the buffer tank. To (further) promote the arrangement of the volume regulating element in the default position in connection with an apparatus stop, the volume regulating element may have gas-filled cavities for increasing its ability of floating. Thus, as an example, during normal operation, the volume regulating element is arranged, by influence of operational forces, in an operation position other than the default position in order for the bath to be filled with sterilization fluid. When an apparatus stop occurs, the operational forces cease, and the volume regulating element is driven towards the default position by the gas-filled cavities and possibly also the spring load. Naturally, the volume regulating element can be made of a material having a lower density than the sterilization fluid so as to spontaneously float on the fluid. However, the gas-filled cavities and the spring load may still be advantageous for the volume regulating element to take the default position faster. In one embodiment of the present invention the apparatus further comprises a pneumatic cylinder for moving the volume regulating element in a way so as to transfer sterilization fluid from the buffer tank to the bath. This embodiment enables a relatively mechanically simple construction of the apparatus. The inventive apparatus can be constructed so that the transfer system further comprises a pump for transferring sterilization liquid from the supply to the buffer tank. Thereby, transfer of sterilization fluid from the supply to the buffer tank, and from the buffer tank to the bath, can be controlled independently of each other. According to one embodiment the apparatus further comprises at least one roller for directing the web through the bath. In this way it can be ensured that the web is properly immerged in the sterilization fluid. The sterilization fluid used in the apparatus can be hydrogen peroxide, which is a well-tested and well-working sterilization liquid in the packaging industry. A method for sterilization of a web of packaging material according to the present invention comprises transferring sterilization fluid from a supply of sterilization fluid to a bath and passing the web through the bath. The method is characterized in further comprising transferring sterilization fluid from the supply to a buffer tank and transferring, by receiving at least a part of a moveable volume regulating element in the buffer tank, sterilization fluid from the buffer tank to the bath. The volume regulating element is arranged to act upon the sterilization fluid in the buffer tank so that a volume of sterilization fluid in the bath is a function of a position of the volume regulating element in the buffer tank. The characteristics discussed in connection with the inventive apparatus for sterilization are, of course, transferable to the inventive method of sterilization. Further, these characteristics may naturally be combined in the same embodiment. BRIEF DESCRIPTION OF THE DRAWINGS The invention will be described in more detail with reference to the appended schematic drawings, which show an example of a presently non-limiting preferred embodiment of the present invention. Figure 1 is a sectional view of an apparatus according to the present invention in an upper extreme condition. Figure 2 is a sectional view of the apparatus of figure 1 in a lower extreme condition. Figure 3 is a perspective view of the apparatus of figures 1 and 2 in the upper extreme condition. Figure 4 is a perspective view of a volume regulating element and an associated control means of the apparatus according to the present invention. Figure 5 is a perspective view of the apparatus of figures 1 and 2 in the upper extreme condition where some parts have been omitted for reasons of clarity. Figure 6 is a perspective view of the apparatus of figures 1 and 2 in the lower extreme condition where some parts have been omitted for reasons of clarity. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS In figures 1, 2 and 3 a sterilization apparatus 10 is shown, through which a web 12 (shown only in figures 1 and 2) of packaging material is passed for sterilization prior to tube forming, filling and transverse sealing, as initially described. At the entrance 14 the web 12, originating from a roll of packaging material (not shown), enters the apparatus 10, and at the exit 16 the web leaves the apparatus to enter a dryer (not shown). The apparatus 10 comprises a lower buffer tank 18 and an upper bath 20. The upper edge of the side wall 22 of the buffer tank 18 is connected to the left edge of the bottom wall 24 of the bath 20, creating a direct transition between the buffer tank and the bath. The bottom wall 24 of the bath 20 is not arranged perpendicular to the side wall 22 of the bath but slop gently down thereto for reasons that will be obvious from the following description. The interior 26 of the buffer tank essentially has the shape of rectangular parallelepiped. An inlet pipe 28 connects the buffer tank 18 to a supply container 30 in which sterilization fluid in the form of liquid hydrogen peroxide is delivered to the plant where the sterilization apparatus is used. The buffer tank 18 may be emptied via an outlet pipe 32 connected to a waste container (not shown). The apparatus 10 further comprises a moveable volume regulating element 34, a first part 36 (limited by the dashed line) of which is arranged to be received in the buffer tank 18. In figure 4, the volume regulating element is illustrated in more detail. The first part 36 has the outer shape of a rectangular parallelepiped provided with a flange 38 protruding form one side 40 of the parallelepiped at the bottom side 42 thereof. The purpose of the flange 38 is to facilitate the arrangement of the web 12 in the sterilization apparatus 10, as will be evident from the following description. As apparent from the figures, with cross sections taken parallel to a direction x illustrated in figures 1 and 2, the cross section of the volume regulating element 34 at its bottom side 42 is essentially uniform to the cross section of the interior 26 of the buffer tank 18, but slightly smaller so that the first part 36 of the volume regulating element 34 can move up and down in the buffer tank 18. The volume regulating element is made of plastic and provided with cavities 44 which open to the bottom side 42 in order to increase its ability of floating, as will be further discussed below. Thus, in the buffer tank 18, the volume regulating element 34 can have different positions between an upper and a lower extreme position, which extreme positions are illustrated in figure 1 and 2, respectively. In the lower extreme position, the bottom side 42 of the volume regulating element 34 is arranged at the bottom wall 46 of the buffer tank 18. Here, the whole first part 36 of the volume regulating element 34 is received in the buffer tank while a second part 48 of the volume regulating element is arranged outside the buffer tank. In the upper extreme position, the bottom side 42 of the volume regulating element 34 is arranged essentially on the same level as the bottom wall 24 of the bath 20. Here, essentially the whole volume regulating element is arranged outside the buffer tank. As apparent from the figures, the volume regulating element thereby forms a moveable side wall 50 (figure 1) of the bath 20, the side wall 50 being composed of the side 40 and the flange 38 of the first part 36 in the upper extreme position, and the side 52 (figure 4) of the second part 48 in the lower extreme position. The upper and lower extreme positions can also be seen in figures 5 and 6, respectively, in which figures the back wall 54 of the sterilization apparatus 10 and the buffer tank 18 has been omitted for reasons of clarity. The sterilization apparatus 10 is provided with a control means 56 for moving the volume regulating element 34 between the different positions in the buffer tank 18. This control means can be seen most clearly in figures 3-6. The control means 56 comprises a pneumatic cylinder 58 for pushing the volume regulating element downwards in the buffer tank. The pneumatic cylinder 58 is connected to a power transmission structure 60, which in turn is connected, at two locations, to the volume regulating element 34. The control means 56 further comprises a spring 62 being connected to the power transmission structure 60 at one end, and to the volume regulating element 34 at the other end. When no power is supplied to the control means 56, the volume regulating element will be arranged in the upper extreme position, as illustrated in figure 5. This is because he upwards directed force acting on the volume regulating element 34 and resul-ing from the spring 62 exceeds the gravity of the volume regulating element. Since the volume regulating element spontaneously will take the upper extreme position in the absence of power, the upper extreme position is the default posi-ion of the volume regulating element. When enough power is supplied to the control means 56, the volume regulating element 34 will be arranged in the lower sxtreme position, as illustrated in figure 6. This is because the downwards direc-:ed forces acting on the volume regulating element 34 and resulting from the pneumatic cylinder under the influence of compressed air and the gravity of the volume regulating element exceed the upwards directed force from the tightened spring 62. The web 12 is passed over three web rollers 64 to be directed through the apparatus and thereby the bath for sterilization. Just below the exit 16 of the apparatus 10, the web passes between two distribution rollers 66, so called squeegee rollers, to achieve an even distribution of the hydrogen peroxide deposited on the web. By means of these distribution rollers a thin film of hydrogen peroxide is obtained across the entire width of the web, thus ensuring proper sterilization. The function of the sterilization apparatus 10 will now be described with reference to the figures. Before the packaging machine of which the sterilization apparatus 10 is a part is started, hydrogen peroxide is pumped from the supply container 30 by means of a pump 68 through the inlet pipe 28 into the buffer tank 18. When the hydrogen peroxide in the buffer tank reaches a predetermined level 70 (figure 1), the pump 68 is stopped whereby the supply through the inlet pipe 28 is interrupted. A sensor 72 is used for determining when the level 70 is reached. To accommodate this sensor, the volume regulating element 34 is provided with a groove 74 (figure 6) Jn connection with packaging machine start-up, the pneumatic cylinder 58 is activated and starts pushing the volume regulating element 34 downwards in the buffer tank 18. The first part 36 of the volume regulating element acts upon hydrogen peroxide in the buffer tank and forces it out of the way. More particularly, the hydrogen peroxide is forced in a direction opposite the moving direction of the volume regulating element, i.e. upwards around the volume regulating element, eventually into the bath 20. As the distance between the bottom side 42 of the volume regulating element and the bottom wall 46 of the buffer tank 18 decreases, the level of hydrogen peroxide in the bath 20 increases. When the volume regulating element reaches the lower extreme position, the filling of the bath is complete and the bath then contains hydrogen peroxide to a predetermined level 76 (figure 2). Since the first part of the volume regulating element fills most of the interior of the buffer tank in this position, most of the hydrogen peroxide initially transferred from the container supply to the buffer tank will now have been further transferred to the bath. The web 12 enters the sterilization apparatus 10 through the entrance 14 and passes around the web rollers 64 through the bath 20. The arrangement of the web rollers and the hydrogen peroxide level 76 in the bath ensure that a suitable portion of the web is properly immerged in hydrogen peroxide. After passing through the bath the web is directed upwards and passes between the squeegee rollers 66. Hydrogen peroxide that has been deposited on the web is thereby evenly distributed over the entire width of the web in the form of a thin film, so that a reliable sterilization of the complete web is ensured. After leaving the sterilization apparatus 10 through the exit 16, the web enters a heating chamber for drying off the hydrogen peroxide. If an apparatus stop should occur, e.g. because of a power failure or a command from the operator, the power supply to the pneumatic cylinder ceases and the volume regulating element is forced, by the spring 62 and the lifting force from the liquid hydrogen peroxide, up and towards the default position, i.e. the upper extreme position. As the volume regulating element moves upwards, the hydrogen peroxide in the bath is drained by gravity to the buffer tank 18. Thereby, edge soaking of hydrogen peroxide into the web of packaging material is prevented. Also, since the hydrogen peroxide is drained into the buffer tank and not back to the supply, there will be no mixing between used and unused hydrogen peroxide. The sloping of the bottom wall 24 of the bath 20 facilitates complete draining of the hydrogen peroxide from the bath to the buffer tank 18. Further, in the default position, the volume regulating element 34 covers, to a large extent, the surface of the hydrogen peroxide in the buffer tank. In this way, an operator that needs to access the area of the bath during a stop is protected from exposure to hydrogen peroxide. One example of such a need-for-access-situation is when a web break occurs and the web needs to be re-threaded through the apparatus. Naturally, even if the bath is completely drained, there will still be residues of hydrogen peroxide on the bottom wall and side walls of the bath. However, under normal conditions, in connection with re-threading of the web, there will be no need for the operator to contact the walls of the bath. The reason for this is that the web will be guided around the roller in the bath by the right sloping side wall 78 (figure 1) of the bath 20 and the flange 38 of the volume regulating element 34. During use in the bath, the hydrogen peroxide may be contaminated by paper dust from the web, and it is also gradually degraded whereby its concentration is lowered. Therefore, after a while, the used hydrogen peroxide needs to be changed. Then, the volume regulating element is arranged in its default position to drain the used hydrogen peroxide out of the bath and into the buffer tank, and from the buffer tank through the outlet pipe 32 to the waste container. New hydrogen peroxide is subsequently pumped by means of the pump 68 from the supply container, through the inlet pipe 28, and into the buffer tank 18 up to the predetermined level 70. In connection with packaging machine restart, the bath can be refilled with hydrogen peroxide in the above described way. Thus, the present invention offers a very robust construction and a smart and economical way of controlling the level of sterilization fluid in the bath in connection with a stoppage of production. Because of the volume regulating element taking up most of the interior of the buffer tank, a highly efficient use of the hydrogen peroxide is enabled since most of the hydrogen peroxide brought from the container supply subsequently will be brought to the bath. Additionally, the mechanical simplicity of the volume regulating element with associated control means involves less wear details as compared to a pump that is traditionally used for the same purpose. Further, the combination of the air-filled cavities, the spring and the pneumatic cylinder enables very fast filling and emptying of the bath. A fast filling of the bath is important in connection with machine start-up. A fast emptying of the bath is important in connection with a machine stop to prevent edge-soaking and make sure that an operator accessing the machine is not subjected to hydrogen peroxide. The emptying/filling speed obtainable by using the invention could be matched only with a pump having very high capacity. Finally, controlling the level of hydrogen peroxide in the bath by raising and lowering the volume regulating element in the buffer tank result in smaller power consumption than using a pump for the same purpose. The above-described embodiment should only be seen as an example. A person skilled in the art realizes that the embodiment discussed can be modified and varied in a number of ways without deviating from the inventive conception. For instance, in the sterilization apparatus described above, hydrogen peroxide has been used as the sterilization fluid. However, other sterilization fluids may be used in connection with the inventive apparatus and method for sterilization. Further, in the above described embodiment the pneumatic cylinder is arranged to push the volume regulating element downwards in the bath. Naturally, the pneumatic cylinder could be further arranged to pull the volume regulating element upwards in connection with an apparatus stop to increase the emptying speed of the bath. However, there would be no upwards directed force resulting from the pneumatic cylinder in case of a machine stop caused by a power failure since power is required for the cylinder to work. Further, in the above described embodiment, the bath has been completely drained in connection with an apparatus stop. However, the apparatus could also be constructed in such a way that the bath is only partially drained when an apparatus stop occurs. As an example, this could be obtained by a construction in which the bottom wall of the bath is sloping in the opposite direction to what has been described above. Such an embodiment could be usable as long as the hydrogen peroxide in the bath reaches a level beneath the web so that edge soaking is prevented. However, with this embodiment there may be a risk that an operator is exposed to hydrogen peroxide when accessing the area of the bath in connection with an apparatus stop. Also, the bath and the buffer tank need not be directly connected to each other like above but could instead be indirectly connected by means of some sort of connection means, such as a tube. However, since gravity is used for draining hydrogen peroxide from the bath to the buffer tank, the bath should be placed higher than the buffer tank. Additionally, the volume regulating element need not be made of plastic, but could be made of any suitable material which is resistant to the sterilization fluid being used. If the lifting force from the sterilization fluid is to be used for bringing the volume regulating element to its default position, it is, of course, beneficial if the density of the material of the volume regulating element is less than the density of the sterilization fluid. Further, in the above described embodiment the volume regulating element has been pushed down into the buffer tank to force the hydrogen peroxide therein upwards and into the bath. The volume regulating element could instead be arranged in the opposite way, i.e. to lift the hydrogen peroxide. In such an embodiment the volume regulating element could, in its default position, be arranged at the bottom wall of the buffer tank. To fill the bath with hydrogen peroxide, the volume regulating element would then be pulled upwards. Of course, this would require a fluid-tight contact between the side walls of the buffer tank and volume regulating element. The interior of the buffer tank and the first part of the volume regulating element need not have the essential shape of rectangular parallelepipeds but can have any shape, such as conical, pyramidal or cubical. Further, in the above described embodiment, in a direction y illustrated in figures 1 and 2, the extension of the volume regulating element is larger than the extension of the buffer tank so that the second part of the volume regulating element extends outside the buffer tank in the lower extreme position to form a side wall of the bath. In an alternative embodiment the volume regulating element can be shorter so as to be completely immerged in the hydrogen peroxide in the buffer tank in the lower extreme position. In such an embodiment, the side wall of the bath would, of course, not be formed by the volume regulating element but in some other way, such as by the back wall 54 which can be seen in figure 3. Finally, it should be pointed out that the figures are not drawn according to scale and that some apparatus components not relevant to the invention have been omitted in some of the figures. CLAIMS 1. An apparatus (10) for sterilization of a web (12) of packaging material, comprising a bath (20) through which the web is to be passed and a transfer system for transferring sterilization fluid from a supply (30) of sterilization fluid to the bath, characterized in that the transfer system comprises a buffer tank (18) to which sterilization fluid is transferred from the supply and a movable volume regulating element (34) for transferring sterilization fluid from the buffer tank to the bath, wherein at least a part (36) of the volume regulating element is arranged to be received in the buffer tank and act upon the sterilization fluid therein, a volume of sterilization fluid in the bath thereby being a function of a position of the volume regulating element in the buffer tank. 2. An apparatus (10) according to claim 1, wherein the volume of sterilization fluid in the bath (20) increases when a distance between said part (36) of the volume regulating element (34) and a bottom wall (46) of the buffer tank (18) decreases. 3. An apparatus (10) according to any one of the preceding claims, wherein said part (36) of the volume regulating element (34) is arranged to force the sterilization fluid in a direction opposite a moving direction of said part of the volume regulating element in the buffer tank. 4. An apparatus (10) according to any one of the preceding claims, wherein a side wall (22) of the buffer tank (18) is directly connected to a bottom wall (24) of the bath (20). 5. An apparatus (10) according to claim 4, wherein an edge of said side wall (22) of the buffer tank is directly connected to an edge of said bottom wall (24) of the bath (20). 6. An apparatus (10) according to any one of the preceding claims, wherein the bath (20) is arranged at a higher level than the buffer tank (18). 7. An apparatus (10) according to any one of the preceding claims, wherein the volume regulating element (34) is arranged to form at least a part of a side wall (50) of the bath (20). 8. An apparatus (10) according to anyone of the preceding claims, wherein the volume regulating element (34) is arranged to take a default position in connection with an apparatus stop, sterilization fluid thereby automatically being drained from the bath (20) to the buffer tank (18). 9. An apparatus (10) according to claim 8, wherein the volume regulating element (34) is spring-loaded so as to strive towards the default position in connection with an apparatus stop. 10. An apparatus (10) according to claim 8 or 9, wherein the volume regulating element (34) is arranged to at least partly cover a surface of the sterilization fluid in the buffer tank (18) in the default position. 11. An apparatus (10) according to anyone of the preceding claims, wherein the volume regulating element (34) has gas-filled cavities (44) for increasing its ability of floating. 12. An apparatus (10) according to any one of the preceding claims, further comprising a pneumatic cylinder (58) for moving the volume regulating element (34) so as to transfer sterilization fluid from the buffer tank (18) to the bath (20). 13. An apparatus (10) according to anyone of the preceding claims, wherein the transfer system further comprises a pump (68) for transferring sterilization liquid from the supply (30) to the buffer tank (18). 14. An apparatus (10) according to anyone of the preceding claims, further comprising at least one roller (64) for directing the web (12) through the bath (20). 15. An apparatus (10) according to anyone of the preceding claims, wherein the sterilization fluid is liquid hydrogen peroxide. 16. A method for sterilization of a web (12) of packaging material, comprising transferring sterilization fluid from a supply (30) of sterilization fluid to a bath (20) and passing the web through the bath, characterized in further comprising transferring sterilization fluid from the supply to a buffer tank (18) and transferring, by receiving at least a part (36) of a moveable volume regulating element (34) in the buffer tank, sterilization fluid from the buffer tank to the bath, the volume regulating element being arranged to act upon the sterilization fluid in the buffer tank so that a volume of sterilization fluid in the bath is a function of a position of the volume regulating element in the buffer tank. 17. A method according to claim 16, wherein the volume of sterilization fluid in the bath (20) increases when a distance between said part (36) of the volume regulating element (34) and a bottom wall (46) of the buffer tank (18) decreases. 18. A method according to claim 16 or 17, wherein transferring sterilization fluid from the buffer tank (18) to the bath (20) comprises forcing the sterilization fluid in a direction opposite a moving direction of said part (36) of the volume regulating element (34) in the buffer tank. 19. A method according to anyone of claims 16-18, further comprising providing an edge of a side wall (22) of the buffer tank (18) in direct connection with an edge of a bottom wall (24) of the bath (20). 20. A method according to anyone of claims 16-19, further comprising providing the bath (20) at a higher level than the buffer tank (18). 21. A method according to anyone of claims 16-20, further comprising letting the volume regulating element (34) form at least a part of a side wall (50) of the bath (20). 22. A method according to anyone of claims 16-21, further comprising letting the volume regulating element (34) take a default position in connection with an apparatus stop, sterilization fluid thereby automatically being drained from the bath (20) to the buffer tank (18). 23. A method according to claim 22, further comprising letting the volume regulating element (34) at least partly cover a surface of the sterilization fluid in the buffer tank (18) in the default position. 24. A method according to anyone of claims 16-23, further comprising directing the web (12) through the bath (20) by means of at least one roller (64). 25. A method according to anyone of claims 16-24, wherein the steriliza tion fluid is liquid hydrogen peroxide.

Full Text

APPARATUS AND METHOD FOR STERILIZATION
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an apparatus for sterilization of a web of packaging material, comprising a bath through which the web is to be passed and a transfer system for transferring sterilization fluid from a supply of sterilization fluid to the bath. The invention also relates to a method for sterilization of a web of packaging material, comprising transferring sterilization fluid from a supply of sterilization fluid to a bath and passing the web through the bath.
BACKGROUND ART
Within packaging technology, use has long been made of packages for packing and transporting beverages such as milk and juice but also other pourable products. A large group of these packages is produced from a laminated packaging material comprising a core layer of, for example, paper or paperboard and an outer, liquid-tight coating of thermoplastic material on at least that side of the core layer which forms the inside of the package. Sometimes the material also includes a gas barrier, for example in the form of an aluminum layer.
Such packaging containers are often produced in that a web of packaging material is formed into a tube by sealing the longitudinal edges of the web in an overlapping condition. The longitudinally sealed tube is continuously filled with a product and then transversally sealed and formed into cushions. The sealing is made along narrow, transverse, mutually spaced apart, sealing zones. The transverse sealing of the tube takes place in a per se known manner substantially at right angles to the longitudinal direction of the tube and constantly in the same plane. The sealed-off portions of the tube thus containing contents are thereafter separated from the tube by means of incisions in these sealing zones and formed into the desired shape. This technology of forming a tube from a web is well known per se and will not be described in detail.
To extend the shelf-life of the products being packed, it is prior known to sterilize the web before the filling operation and sometimes also the forming operation. Depending on the desired length of the shelf-life and whether the packages should be distributed and stored in a chilled or an ambient environment, different levels of sterilization can be chosen. One way of sterilizing a web of packaging material is chemical sterilization.
In known machines for producing packages in the above described way, the web of packaging material is often chemically sterilized by being passed through a bath of hydrogen peroxide. For various reasons, an operator of such a

machine sometimes needs to stop the machine operation, and thereby the web feeding, for shorter or longer periods of time. If the packaging material is of the initially described kind, i.e. a laminate with a core layer of paper covered on both sides with a liquid-tight coating of thermoplastic material, such stops could entail a risk of hydrogen peroxide being soaked into the paper core layer of the packaging material at the edges of the portion of the web that is immerged in the bath. One problem with such edge soaking of hydrogen peroxide is that it could lead to problems in connection with subsequent sealing. In connection with machine stops, the hydrogen peroxide may therefore be taken out of the bath and back into the supply container from where it was initially brought. However, in this way, unused hydrogen peroxide in the supply container is mixed with the used hydrogen peroxide from the bath. This is somewhat undesirable since the used hydrogen peroxide may be contaminated with e.g. paper dust from the packaging material. Further, the used hydrogen peroxide may be degraded, thereby having a lower concentration compared to the unused hydrogen peroxide. For this reason, this emptying of the bath is normally done only in connection with longer stops in order to avoid unnecessary mixing of new and used hydrogen peroxide. Thus, in connection with short stops, hydrogen peroxide is still present in the bath involving a risk of edge soaking in a portion of the web.
Pumps are traditionally used for transferring the hydrogen peroxide between the supply container and the bath. Such pumps comprise a large number of moving parts, making them relatively complex. Further, since such pumps have a large number of wear details, their lives are relatively limited.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an apparatus and a method for sterilization of a web of packaging material, which apparatus and method, at least partly, eliminate potential limitations of prior art. A basic concept of the invention is to provide a possibility for a supply of sterilization fluid to communicate indirectly with a bath through a buffer tank. Thereby, if the bath is to be emptied, used sterilization fluid can be returned to the buffer tank instead of the supply. Another basic concept of the invention is to provide a reliable, robust and durable element for transferring sterilization fluid from the buffer tank to the bath.
The apparatus and method for achieving the objective above are defined in the appended claims and discussed below.
An apparatus for sterilization of a web of packaging material according to the present invention comprises a bath through which the web is to be passed and a transfer system for transferring sterilization fluid from a supply of steriliza-

tion fluid to the bath. The apparatus is characterized in that the transfer system comprises a buffer tank to which sterilization fluid is transferred from the supply and a movable volume regulating element for transferring sterilization fluid from the buffer tank to the bath. At least a part of the volume regulating element is arranged to be received in the buffer tank and act upon the sterilization fluid therein, a volume of sterilization fluid in the bath thereby being a function of a position of the volume regulating element in the buffer tank. The buffer tank makes it possible to empty the bath without mixing used and unused sterilization fluid. Therefore, the bath can advantageously be emptied in connection with all machine stops, long ones all well as short ones.
By bath is meant a space that can be empty or filled and normally is limited by walls. Thus, with a vessel taken as an example, the bath is the interior of the vessel.
Unless the supply is starting to go dry, it normally contains a relatively large volume of sterilization fluid compared to the volume of sterilization fluid needed to fill the bath to a sufficient level for sterilization of the web. In connection with apparatus start up, when the buffer tank and the bath is empty, sterilization fluid needs to be transferred from the supply to the buffer tank. After that, by means of the volume regulating element, at least some of the sterilization fluid should be transferred from the buffer tank to the bath. The fluid volume that needs to be transferred from the supply to the buffer tank is dependent on the construction of the volume regulating element. In an optimal case, where the volume regulating element is capable of transferring essentially all of the sterilization fluid from the buffer tank to the bath, the fluid volume that needs to be transferred from the supply to the buffer tank is essentially equal to the volume of sterilization fluid in the bath when this is filled to the sufficient level for sterilization. Hereby, the sterilization fluid can be used a particularly beneficial way.
The volume regulating element is arranged to act on the sterilization fluid in the buffer tank to transfer at least a part of the fluid to the bath. This is done by some kind of movement of the volume regulating element in the bath, such as a lateral movement, rotational movement or a combination of these. By providing the apparatus with a volume regulating element working like this, instead of a traditional pump, the level of sterilization fluid in the bath can be controlled in a very neat way. Additionally, since the volume of sterilization fluid in the bath is a function of the position of the volume regulating element in the buffer tank, the speed by which the bath can be filled/emptied with/of sterilization fluid is dependent on the speed of the movement of the volume regulating element in the buffer

tank. Thus, the faster movement of the volume regulating element in the bath, the faster filling/emptying of the bath can be obtained.
In accordance with one embodiment, the apparatus can be constructed so that the volume of sterilization fluid in the bath increases when a distance between said part of the volume regulating element and a bottom wall of the buffer tank decreases. Here, the volume regulating element is arranged for lateral movement to push the sterilization fluid out of its way and directly or indirectly into the bath. This embodiment enables a relatively mechanically simple construction of the volume regulating element.
According to one embodiment, said part of the volume regulating element is arranged to force the sterilization fluid in a direction opposite a moving direction of said part of the volume regulating element in the buffer tank. This could, as an example, mean that the fluid is pressed upwards and around the volume regulating element when the volume regulating element is moving downwards. Such a construction is beneficial since no extra means may be needed for bringing the fluid forced aside by the volume regulating element to the bath, the fluid instead being guided between the volume regulating element and the side wall(s) of the buffer tank.
The inventive apparatus could be constructed in such a way that a side wall of the buffer tank is directly connected to a bottom wall of the bath. Further, it could be constructed with an edge of said side wall of the buffer tank being directly connected to an edge of said bottom wall of the bath. The last configuration means a direct transition from the buffer tank to the bath, wherein sterilization fluid forced out of the buffer tank by means of the volume regulating element automatically ends up in the bath.
According to one embodiment of the inventive apparatus, the bath is arranged at a higher level than the buffer tank. This means that sterilization fluid in the bath can be drained to the buffer tank by gravity. This embodiment is beneficial since additional means, such as pumps, may not be needed for draining the bath.
The apparatus can, in accordance with one embodiment, be constructed so that the volume regulating element is arranged to form at least a part of a side wall of the bath. Such a construction enables a particularly smart design of the apparatus as regards convenient limitation of the bath, rapid filling and emptying of the same, as well as good thrift of sterilization fluid.
As described above, the bath of known packaging machines is emptied in connection with longer machine stops in order to avoid edge soaking into the web. The emptying is performed by means of a pump. However, if a machine

stop is caused by a power failure, it is not possible to empty the bath since electricity is required for the pump to work. Thus, in connection with not only short stops but also power failures, sterilization fluid is still present in the bath of known machines. This involves a risk of edge soaking in a portion of the web. Also, if there should be a need for the operator to access the machine in the area of the bath during a short stop or a power failure, e.g. because of repairs or maintenance, he/she could be subjected to a risk of unhealthy exposure to sterilization fluid.
However, in accordance with one embodiment of the present invention, the volume regulating element is arranged to take a default position in connection with an apparatus stop, sterilization fluid thereby automatically being drained from the bath to the buffer tank. This property makes emptying of the bath very fast and easy, even in connection with apparatus stops in the form of power failures. Thus, in connection with an apparatus stop, the bath is automatically drained, whereby edge soaking into the web of packaging material is prevented. The bath need not be completely drained to achieve this result, but only to a level beneath the material web. However, to ensure that an operator, who is accessing the area of the bath in connection with the apparatus stop, is not exposed to the sterilization fluid, the bath should be completely drained.
By apparatus stop is meant a condition where the web of packaging material is kept still in the bath.
To promote the arrangement of the volume regulating element in the default position in connection with an apparatus stop, the volume regulating element can be spring-loaded so as to strive towards this position in connection with a stop.
According to one embodiment, the volume regulating element is arranged to at least partly cover a surface of the sterilization fluid in the buffer tank in the default position. This embodiment is advantageous since the volume regulating element thereby will help prevent an operator accessing the apparatus from being exposed to the sterilization fluid in the buffer tank.
To (further) promote the arrangement of the volume regulating element in the default position in connection with an apparatus stop, the volume regulating element may have gas-filled cavities for increasing its ability of floating. Thus, as an example, during normal operation, the volume regulating element is arranged, by influence of operational forces, in an operation position other than the default position in order for the bath to be filled with sterilization fluid. When an apparatus stop occurs, the operational forces cease, and the volume regulating element is driven towards the default position by the gas-filled cavities and possibly also the

spring load. Naturally, the volume regulating element can be made of a material having a lower density than the sterilization fluid so as to spontaneously float on the fluid. However, the gas-filled cavities and the spring load may still be advantageous for the volume regulating element to take the default position faster.
In one embodiment of the present invention the apparatus further comprises a pneumatic cylinder for moving the volume regulating element in a way so as to transfer sterilization fluid from the buffer tank to the bath. This embodiment enables a relatively mechanically simple construction of the apparatus.
The inventive apparatus can be constructed so that the transfer system further comprises a pump for transferring sterilization liquid from the supply to the buffer tank. Thereby, transfer of sterilization fluid from the supply to the buffer tank, and from the buffer tank to the bath, can be controlled independently of each other.
According to one embodiment the apparatus further comprises at least one roller for directing the web through the bath. In this way it can be ensured that the web is properly immerged in the sterilization fluid.
The sterilization fluid used in the apparatus can be hydrogen peroxide, which is a well-tested and well-working sterilization liquid in the packaging industry.
A method for sterilization of a web of packaging material according to the present invention comprises transferring sterilization fluid from a supply of sterilization fluid to a bath and passing the web through the bath. The method is characterized in further comprising transferring sterilization fluid from the supply to a buffer tank and transferring, by receiving at least a part of a moveable volume regulating element in the buffer tank, sterilization fluid from the buffer tank to the bath. The volume regulating element is arranged to act upon the sterilization fluid in the buffer tank so that a volume of sterilization fluid in the bath is a function of a position of the volume regulating element in the buffer tank.
The characteristics discussed in connection with the inventive apparatus for sterilization are, of course, transferable to the inventive method of sterilization. Further, these characteristics may naturally be combined in the same embodiment.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be described in more detail with reference to the appended schematic drawings, which show an example of a presently non-limiting preferred embodiment of the present invention.

Figure 1 is a sectional view of an apparatus according to the present invention in an upper extreme condition.
Figure 2 is a sectional view of the apparatus of figure 1 in a lower extreme condition.
Figure 3 is a perspective view of the apparatus of figures 1 and 2 in the upper extreme condition.
Figure 4 is a perspective view of a volume regulating element and an associated control means of the apparatus according to the present invention.
Figure 5 is a perspective view of the apparatus of figures 1 and 2 in the upper extreme condition where some parts have been omitted for reasons of clarity.
Figure 6 is a perspective view of the apparatus of figures 1 and 2 in the lower extreme condition where some parts have been omitted for reasons of clarity.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
In figures 1, 2 and 3 a sterilization apparatus 10 is shown, through which a web 12 (shown only in figures 1 and 2) of packaging material is passed for sterilization prior to tube forming, filling and transverse sealing, as initially described. At the entrance 14 the web 12, originating from a roll of packaging material (not shown), enters the apparatus 10, and at the exit 16 the web leaves the apparatus to enter a dryer (not shown).
The apparatus 10 comprises a lower buffer tank 18 and an upper bath 20. The upper edge of the side wall 22 of the buffer tank 18 is connected to the left edge of the bottom wall 24 of the bath 20, creating a direct transition between the buffer tank and the bath. The bottom wall 24 of the bath 20 is not arranged perpendicular to the side wall 22 of the bath but slop gently down thereto for reasons that will be obvious from the following description. The interior 26 of the buffer tank essentially has the shape of rectangular parallelepiped. An inlet pipe 28 connects the buffer tank 18 to a supply container 30 in which sterilization fluid in the form of liquid hydrogen peroxide is delivered to the plant where the sterilization apparatus is used. The buffer tank 18 may be emptied via an outlet pipe 32 connected to a waste container (not shown).
The apparatus 10 further comprises a moveable volume regulating element 34, a first part 36 (limited by the dashed line) of which is arranged to be received in the buffer tank 18. In figure 4, the volume regulating element is illustrated in more detail. The first part 36 has the outer shape of a rectangular parallelepiped provided with a flange 38 protruding form one side 40 of the

parallelepiped at the bottom side 42 thereof. The purpose of the flange 38 is to facilitate the arrangement of the web 12 in the sterilization apparatus 10, as will be evident from the following description. As apparent from the figures, with cross sections taken parallel to a direction x illustrated in figures 1 and 2, the cross section of the volume regulating element 34 at its bottom side 42 is essentially uniform to the cross section of the interior 26 of the buffer tank 18, but slightly smaller so that the first part 36 of the volume regulating element 34 can move up and down in the buffer tank 18. The volume regulating element is made of plastic and provided with cavities 44 which open to the bottom side 42 in order to increase its ability of floating, as will be further discussed below.
Thus, in the buffer tank 18, the volume regulating element 34 can have different positions between an upper and a lower extreme position, which extreme positions are illustrated in figure 1 and 2, respectively. In the lower extreme position, the bottom side 42 of the volume regulating element 34 is arranged at the bottom wall 46 of the buffer tank 18. Here, the whole first part 36 of the volume regulating element 34 is received in the buffer tank while a second part 48 of the volume regulating element is arranged outside the buffer tank. In the upper extreme position, the bottom side 42 of the volume regulating element 34 is arranged essentially on the same level as the bottom wall 24 of the bath 20. Here, essentially the whole volume regulating element is arranged outside the buffer tank. As apparent from the figures, the volume regulating element thereby forms a moveable side wall 50 (figure 1) of the bath 20, the side wall 50 being composed of the side 40 and the flange 38 of the first part 36 in the upper extreme position, and the side 52 (figure 4) of the second part 48 in the lower extreme position. The upper and lower extreme positions can also be seen in figures 5 and 6, respectively, in which figures the back wall 54 of the sterilization apparatus 10 and the buffer tank 18 has been omitted for reasons of clarity.
The sterilization apparatus 10 is provided with a control means 56 for moving the volume regulating element 34 between the different positions in the buffer tank 18. This control means can be seen most clearly in figures 3-6. The control means 56 comprises a pneumatic cylinder 58 for pushing the volume regulating element downwards in the buffer tank. The pneumatic cylinder 58 is connected to a power transmission structure 60, which in turn is connected, at two locations, to the volume regulating element 34. The control means 56 further comprises a spring 62 being connected to the power transmission structure 60 at one end, and to the volume regulating element 34 at the other end. When no power is supplied to the control means 56, the volume regulating element will be arranged in the upper extreme position, as illustrated in figure 5. This is because

he upwards directed force acting on the volume regulating element 34 and resul-ing from the spring 62 exceeds the gravity of the volume regulating element. Since the volume regulating element spontaneously will take the upper extreme position in the absence of power, the upper extreme position is the default posi-ion of the volume regulating element. When enough power is supplied to the control means 56, the volume regulating element 34 will be arranged in the lower sxtreme position, as illustrated in figure 6. This is because the downwards direc-:ed forces acting on the volume regulating element 34 and resulting from the pneumatic cylinder under the influence of compressed air and the gravity of the volume regulating element exceed the upwards directed force from the tightened spring 62.
The web 12 is passed over three web rollers 64 to be directed through the apparatus and thereby the bath for sterilization. Just below the exit 16 of the apparatus 10, the web passes between two distribution rollers 66, so called squeegee rollers, to achieve an even distribution of the hydrogen peroxide deposited on the web. By means of these distribution rollers a thin film of hydrogen peroxide is obtained across the entire width of the web, thus ensuring proper sterilization.
The function of the sterilization apparatus 10 will now be described with reference to the figures.
Before the packaging machine of which the sterilization apparatus 10 is a part is started, hydrogen peroxide is pumped from the supply container 30 by means of a pump 68 through the inlet pipe 28 into the buffer tank 18. When the hydrogen peroxide in the buffer tank reaches a predetermined level 70 (figure 1), the pump 68 is stopped whereby the supply through the inlet pipe 28 is interrupted. A sensor 72 is used for determining when the level 70 is reached. To accommodate this sensor, the volume regulating element 34 is provided with a groove 74 (figure 6) Jn connection with packaging machine start-up, the pneumatic cylinder 58 is activated and starts pushing the volume regulating element 34 downwards in the buffer tank 18. The first part 36 of the volume regulating element acts upon hydrogen peroxide in the buffer tank and forces it out of the way. More particularly, the hydrogen peroxide is forced in a direction opposite the moving direction of the volume regulating element, i.e. upwards around the volume regulating element, eventually into the bath 20. As the distance between the bottom side 42 of the volume regulating element and the bottom wall 46 of the buffer tank 18 decreases, the level of hydrogen peroxide in the bath 20 increases. When the volume regulating element reaches the lower extreme position, the filling of the bath is complete and the bath then contains hydrogen peroxide to a

predetermined level 76 (figure 2). Since the first part of the volume regulating element fills most of the interior of the buffer tank in this position, most of the hydrogen peroxide initially transferred from the container supply to the buffer tank will now have been further transferred to the bath.
The web 12 enters the sterilization apparatus 10 through the entrance 14 and passes around the web rollers 64 through the bath 20. The arrangement of the web rollers and the hydrogen peroxide level 76 in the bath ensure that a suitable portion of the web is properly immerged in hydrogen peroxide. After passing through the bath the web is directed upwards and passes between the squeegee rollers 66. Hydrogen peroxide that has been deposited on the web is thereby evenly distributed over the entire width of the web in the form of a thin film, so that a reliable sterilization of the complete web is ensured. After leaving the sterilization apparatus 10 through the exit 16, the web enters a heating chamber for drying off the hydrogen peroxide.
If an apparatus stop should occur, e.g. because of a power failure or a command from the operator, the power supply to the pneumatic cylinder ceases and the volume regulating element is forced, by the spring 62 and the lifting force from the liquid hydrogen peroxide, up and towards the default position, i.e. the upper extreme position. As the volume regulating element moves upwards, the hydrogen peroxide in the bath is drained by gravity to the buffer tank 18. Thereby, edge soaking of hydrogen peroxide into the web of packaging material is prevented. Also, since the hydrogen peroxide is drained into the buffer tank and not back to the supply, there will be no mixing between used and unused hydrogen peroxide.
The sloping of the bottom wall 24 of the bath 20 facilitates complete draining of the hydrogen peroxide from the bath to the buffer tank 18. Further, in the default position, the volume regulating element 34 covers, to a large extent, the surface of the hydrogen peroxide in the buffer tank. In this way, an operator that needs to access the area of the bath during a stop is protected from exposure to hydrogen peroxide. One example of such a need-for-access-situation is when a web break occurs and the web needs to be re-threaded through the apparatus. Naturally, even if the bath is completely drained, there will still be residues of hydrogen peroxide on the bottom wall and side walls of the bath. However, under normal conditions, in connection with re-threading of the web, there will be no need for the operator to contact the walls of the bath. The reason for this is that the web will be guided around the roller in the bath by the right sloping side wall 78 (figure 1) of the bath 20 and the flange 38 of the volume regulating element 34.

During use in the bath, the hydrogen peroxide may be contaminated by paper dust from the web, and it is also gradually degraded whereby its concentration is lowered. Therefore, after a while, the used hydrogen peroxide needs to be changed. Then, the volume regulating element is arranged in its default position to drain the used hydrogen peroxide out of the bath and into the buffer tank, and from the buffer tank through the outlet pipe 32 to the waste container. New hydrogen peroxide is subsequently pumped by means of the pump 68 from the supply container, through the inlet pipe 28, and into the buffer tank 18 up to the predetermined level 70. In connection with packaging machine restart, the bath can be refilled with hydrogen peroxide in the above described way.
Thus, the present invention offers a very robust construction and a smart and economical way of controlling the level of sterilization fluid in the bath in connection with a stoppage of production. Because of the volume regulating element taking up most of the interior of the buffer tank, a highly efficient use of the hydrogen peroxide is enabled since most of the hydrogen peroxide brought from the container supply subsequently will be brought to the bath. Additionally, the mechanical simplicity of the volume regulating element with associated control means involves less wear details as compared to a pump that is traditionally used for the same purpose. Further, the combination of the air-filled cavities, the spring and the pneumatic cylinder enables very fast filling and emptying of the bath. A fast filling of the bath is important in connection with machine start-up. A fast emptying of the bath is important in connection with a machine stop to prevent edge-soaking and make sure that an operator accessing the machine is not subjected to hydrogen peroxide. The emptying/filling speed obtainable by using the invention could be matched only with a pump having very high capacity. Finally, controlling the level of hydrogen peroxide in the bath by raising and lowering the volume regulating element in the buffer tank result in smaller power consumption than using a pump for the same purpose.
The above-described embodiment should only be seen as an example. A person skilled in the art realizes that the embodiment discussed can be modified and varied in a number of ways without deviating from the inventive conception.
For instance, in the sterilization apparatus described above, hydrogen peroxide has been used as the sterilization fluid. However, other sterilization fluids may be used in connection with the inventive apparatus and method for sterilization.
Further, in the above described embodiment the pneumatic cylinder is arranged to push the volume regulating element downwards in the bath. Naturally, the pneumatic cylinder could be further arranged to pull the volume regulating

element upwards in connection with an apparatus stop to increase the emptying speed of the bath. However, there would be no upwards directed force resulting from the pneumatic cylinder in case of a machine stop caused by a power failure since power is required for the cylinder to work.
Further, in the above described embodiment, the bath has been completely drained in connection with an apparatus stop. However, the apparatus could also be constructed in such a way that the bath is only partially drained when an apparatus stop occurs. As an example, this could be obtained by a construction in which the bottom wall of the bath is sloping in the opposite direction to what has been described above. Such an embodiment could be usable as long as the hydrogen peroxide in the bath reaches a level beneath the web so that edge soaking is prevented. However, with this embodiment there may be a risk that an operator is exposed to hydrogen peroxide when accessing the area of the bath in connection with an apparatus stop.
Also, the bath and the buffer tank need not be directly connected to each other like above but could instead be indirectly connected by means of some sort of connection means, such as a tube. However, since gravity is used for draining hydrogen peroxide from the bath to the buffer tank, the bath should be placed higher than the buffer tank.
Additionally, the volume regulating element need not be made of plastic, but could be made of any suitable material which is resistant to the sterilization fluid being used. If the lifting force from the sterilization fluid is to be used for bringing the volume regulating element to its default position, it is, of course, beneficial if the density of the material of the volume regulating element is less than the density of the sterilization fluid.
Further, in the above described embodiment the volume regulating element has been pushed down into the buffer tank to force the hydrogen peroxide therein upwards and into the bath. The volume regulating element could instead be arranged in the opposite way, i.e. to lift the hydrogen peroxide. In such an embodiment the volume regulating element could, in its default position, be arranged at the bottom wall of the buffer tank. To fill the bath with hydrogen peroxide, the volume regulating element would then be pulled upwards. Of course, this would require a fluid-tight contact between the side walls of the buffer tank and volume regulating element.
The interior of the buffer tank and the first part of the volume regulating element need not have the essential shape of rectangular parallelepipeds but can have any shape, such as conical, pyramidal or cubical.

Further, in the above described embodiment, in a direction y illustrated in figures 1 and 2, the extension of the volume regulating element is larger than the extension of the buffer tank so that the second part of the volume regulating element extends outside the buffer tank in the lower extreme position to form a side wall of the bath. In an alternative embodiment the volume regulating element can be shorter so as to be completely immerged in the hydrogen peroxide in the buffer tank in the lower extreme position. In such an embodiment, the side wall of the bath would, of course, not be formed by the volume regulating element but in some other way, such as by the back wall 54 which can be seen in figure 3.
Finally, it should be pointed out that the figures are not drawn according to scale and that some apparatus components not relevant to the invention have been omitted in some of the figures.

CLAIMS
1. An apparatus (10) for sterilization of a web (12) of packaging material, comprising a bath (20) through which the web is to be passed and a transfer system for transferring sterilization fluid from a supply (30) of sterilization fluid to the bath, characterized in that the transfer system comprises a buffer tank (18) to which sterilization fluid is transferred from the supply and a movable volume regulating element (34) for transferring sterilization fluid from the buffer tank to the bath, wherein at least a part (36) of the volume regulating element is arranged to be received in the buffer tank and act upon the sterilization fluid therein, a volume of sterilization fluid in the bath thereby being a function of a position of the volume regulating element in the buffer tank.
2. An apparatus (10) according to claim 1, wherein the volume of sterilization fluid in the bath (20) increases when a distance between said part (36) of the volume regulating element (34) and a bottom wall (46) of the buffer tank (18) decreases.
3. An apparatus (10) according to any one of the preceding claims, wherein said part (36) of the volume regulating element (34) is arranged to force the sterilization fluid in a direction opposite a moving direction of said part of the volume regulating element in the buffer tank.
4. An apparatus (10) according to any one of the preceding claims, wherein a side wall (22) of the buffer tank (18) is directly connected to a bottom wall (24) of the bath (20).
5. An apparatus (10) according to claim 4, wherein an edge of said side wall (22) of the buffer tank is directly connected to an edge of said bottom wall (24) of the bath (20).
6. An apparatus (10) according to any one of the preceding claims, wherein the bath (20) is arranged at a higher level than the buffer tank (18).
7. An apparatus (10) according to any one of the preceding claims, wherein the volume regulating element (34) is arranged to form at least a part of a side wall (50) of the bath (20).
8. An apparatus (10) according to anyone of the preceding claims, wherein the volume regulating element (34) is arranged to take a default position in connection with an apparatus stop, sterilization fluid thereby automatically being drained from the bath (20) to the buffer tank (18).
9. An apparatus (10) according to claim 8, wherein the volume regulating element (34) is spring-loaded so as to strive towards the default position in connection with an apparatus stop.

10. An apparatus (10) according to claim 8 or 9, wherein the volume regulating element (34) is arranged to at least partly cover a surface of the sterilization fluid in the buffer tank (18) in the default position.
11. An apparatus (10) according to anyone of the preceding claims, wherein the volume regulating element (34) has gas-filled cavities (44) for increasing its ability of floating.
12. An apparatus (10) according to any one of the preceding claims, further comprising a pneumatic cylinder (58) for moving the volume regulating element (34) so as to transfer sterilization fluid from the buffer tank (18) to the bath (20).
13. An apparatus (10) according to anyone of the preceding claims, wherein the transfer system further comprises a pump (68) for transferring sterilization liquid from the supply (30) to the buffer tank (18).
14. An apparatus (10) according to anyone of the preceding claims, further comprising at least one roller (64) for directing the web (12) through the bath (20).
15. An apparatus (10) according to anyone of the preceding claims, wherein the sterilization fluid is liquid hydrogen peroxide.
16. A method for sterilization of a web (12) of packaging material, comprising transferring sterilization fluid from a supply (30) of sterilization fluid to a bath (20) and passing the web through the bath, characterized in further comprising transferring sterilization fluid from the supply to a buffer tank (18) and transferring, by receiving at least a part (36) of a moveable volume regulating element (34) in the buffer tank, sterilization fluid from the buffer tank to the bath, the volume regulating element being arranged to act upon the sterilization fluid in the buffer tank so that a volume of sterilization fluid in the bath is a function of a position of the volume regulating element in the buffer tank.
17. A method according to claim 16, wherein the volume of sterilization fluid in the bath (20) increases when a distance between said part (36) of the volume regulating element (34) and a bottom wall (46) of the buffer tank (18) decreases.
18. A method according to claim 16 or 17, wherein transferring sterilization fluid from the buffer tank (18) to the bath (20) comprises forcing the sterilization fluid in a direction opposite a moving direction of said part (36) of the volume regulating element (34) in the buffer tank.
19. A method according to anyone of claims 16-18, further comprising providing an edge of a side wall (22) of the buffer tank (18) in direct connection with an edge of a bottom wall (24) of the bath (20).

20. A method according to anyone of claims 16-19, further comprising
providing the bath (20) at a higher level than the buffer tank (18).
21. A method according to anyone of claims 16-20, further comprising
letting the volume regulating element (34) form at least a part of a side wall (50)
of the bath (20).
22. A method according to anyone of claims 16-21, further comprising
letting the volume regulating element (34) take a default position in connection
with an apparatus stop, sterilization fluid thereby automatically being drained from
the bath (20) to the buffer tank (18).
23. A method according to claim 22, further comprising letting the volume
regulating element (34) at least partly cover a surface of the sterilization fluid in
the buffer tank (18) in the default position.
24. A method according to anyone of claims 16-23, further comprising
directing the web (12) through the bath (20) by means of at least one roller (64).
25. A method according to anyone of claims 16-24, wherein the steriliza
tion fluid is liquid hydrogen peroxide.

Documents:

1884-CHE-2005 AMENDED CLAIMS 09-02-2012.pdf

1884-CHE-2005 EXAMINATION REPORT REPLY RECEIVED 09-02-2012.pdf

1884-CHE-2005 FORM-3 09-02-2012.pdf

1884-CHE-2005 POWER OF ATTORNEY 09-02-2012.pdf

1884-CHE-2005 CORRESPONDENCE PO.pdf

1884-CHE-2005 FORM-18.pdf

1884-che-2005-abstract image.jpg

1884-che-2005-abstract.pdf

1884-che-2005-claims.pdf

1884-che-2005-correspondnece-others.pdf

1884-che-2005-description(complete).pdf

1884-che-2005-drawings.pdf

1884-che-2005-form 1.pdf

1884-che-2005-form 26.pdf

1884-che-2005-form 3.pdf

1884-che-2005-form 5.pdf

1884-che-2005-others docuemnt.pdf

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Patent Number

251288

Indian Patent Application Number

1884/CHE/2005

PG Journal Number

10/2012

Publication Date

09-Mar-2012

Grant Date

05-Mar-2012

Date of Filing

22-Dec-2005

Name of Patentee

TETRA LAVAL HOLDINGS & FINANCE SA

Applicant Address

70 AVENUE GENERAL GUISAN CH 1009 PULLY

Inventors:

#	Inventor's Name	Inventor's Address
1	SVENLE MARTIN	OROD 1297 S 280 60 BROBY

PCT International Classification Number

B65B55/04

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	0403159-7	2004-12-22	Sweden