Title of Invention

AN APPARATUS AND A METHOD FOR STERILIZATION OF A WEB OF PACKAGING MATERIAL

Abstract

An apparatus (1) for sterilization of a web (2) of packaging material comprises a tub (6) through which the web (2) is to be passed, a supply (16) of sterilization liquid and a transfer system (5, 7, 9, 17) for transferring sterilization liquid from the supply (16) to the tub (6). The transfer system comprises a buffer tank (5) to which sterilization liquid is transferred from the supply (16) and a transfer device (9) for transferring sterilization liquid from the buffer tank (5) to the tub (6). The tub (6) is provided with self-draining means (11) for returning the sterilization liquid to the buffer tank (5) when the web (2) is kept still in the tub (6). A method for sterilization of a web of packaging material is also disclosed. Elected for publication: Fig. 2

Full Text

STERILIZATION APPARATUS AND METHOD Technical Field of the Invention The present invention relates to an apparatus for sterilization of a web of packaging material, comprising a tub through which the web is to be passed, a supply of sterilization liquid and a transfer system for transferring sterilization liquid from the supply to the tub. The invention also relates to a method for sterilization of a web of packaging material, wherein the web is passed through a tub containing a sterilization liquid. Background Art Within packaging technology, use has long been made of packages for packing and transporting products such as milk, juice and other beverages. A large group of these packages is produced from a laminated packaging material comprising a core layer of, for example, paper or paper-board 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 aluminium layer. Such packaging containers are often produced in that a web of packaging material is formed into a tube by overlappingly sealing the longitudinal edges of the web. The 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. This technology of forming a tube from a web is well known per se and will not be described in detail. The cushion-shaped packages have been commercialised by the applicant under the trade name Tetra Fino. To extend the shelf-life of the products being packed it is prior known to sterilise the web before the forming and filling operations. Depending on how long shelf-life is desired and whether the distribution and storage is made in chilled or ambient temperature, different levels of sterilization can be chosen. One way of sterilising a web is chemical sterilization using for example a bath of hydrogen peroxide. In known machines for forming packages from a web of packaging material the web is often passed through a bath of hydrogen peroxide. For various reasons, the operator of the machine sometimes needs to stop the machine for a shorter or longer period of time, and if the hydrogen peroxide is kept in the bath during such stops there is sometimes a risk that the hydrogen peroxide is soaked into the edges of the portion of the web that is immerged in the hydrogen peroxide bath. During longer stops the hydrogen peroxide is therefore pumped out of the bath and back into the supply container in which it was bought. However, in this way the new hydrogen peroxide still left in the container is mixed with the used hydrogen peroxide which has been in the bath. This is somewhat undesirable since the used hydrogen peroxide may be contaminated with paper dust from the web and may have degraded, so that the concentration is lowered. This emptying of the bath is therefore normally only done during longer stops, in order to avoid unnecessary mixing of new and used hydrogen peroxide. Further, if a stop is caused by a power failure it is not possible to empty the bath, since electricity is needed for the pump. Thus, during short stops and during power failure hydrogen peroxide is still present in the bath and there is thus a risk that it will be soaked into the web, making that portion of the web unsuitable because of potential problems during sealing. Summary of the Invention An object of the present invention is therefore to provide an apparatus and a method that make it possible to eliminate the risk of edge soaking, also during short stops and power failures. Yet another object is to provide an apparatus that is more reliable and uses few moving parts. These objects are achieved by means of an apparatus according to claim 1, preferred embodiments being defined in the dependent claims 2-9. These objects are also achieved by means of a method according to claim 10, preferred variants thereof being defined in claims 11-15. The apparatus of the invention has a transfer system that comprises a buffer tank to which sterilization liquid is transferred from the supply and a transfer device for transferring sterilization liquid from the buffer tank to the tub, wherein the tub is provided with self-draining means for returning the sterilization liquid to the buffer tank when the web is kept still in the tub. The buffer tank makes it possible to empty the tub without mixing new and used sterilization liquid and the self-draining property of the tub makes it particularly easy to empty it, even during power failure. Preferably, the transfer device for transferring sterilization liquid from the buffer tank to the tub is a first pump and the transfer system further comprises a second pump for transferring sterilization liquid from the supply to the buffer tank. Transfer of sterilization liquid to the buffer tank and to the tub can in this way easily be controlled, independently of each other. In another variant, the transfer device for transferring sterilization liquid from the buffer tank to the tub is a first pump, said first pump additionally being arranged to transfer sterilization liquid from the supply to the buffer tank. With this configuration, a single pump may be used for pumping sterilization liquid both from the supply to the buffer tank and from the buffer tank to the tub, thus making it possible to reduce the number of parts of the apparatus. In one embodiment, the self-draining means of the tub is arranged to return the sterilization liquid to the buffer tank when the first pump is not pumping sterilization liquid to the tub. In this manner it is assured that during power failure the tub is reliably drained. In a preferred embodiment of the invention, the self-draining means of the tub is arranged to continuously return the sterilization liquid to the buffer tank as long as there is sterilization liquid in the tub. This construction makes it particularly easy to guarantee that no sterilization liquid is left in the tub when the machine has stopped. The tub is preferably arranged at a higher level than the buffer tank and the self-draining means of the tub is preferably at least one hole at a bottom of the tub for returning the sterilization liquid to the buffer tank when the web is kept still in the tub. This is a mechanically simple variant of self-draining. A pair of distribution rollers are advantageously arranged downstream of the tub in a direction of travel of the web, said rollers being arranged to evenly distribute the sterilization liquid deposited on the web. By means of the distribution rollers a thin film of sterilization liquid may be spread across the entire width of the web, thus ensuring proper sterilization. The apparatus of the invention may further comprise web rollers for directing the web through the tub. In this way it may be ensured that the web is properly im-merged in the sterilization liquid. The sterilization liquid is advantageously hydrogen peroxide, which is a well-tested sterilization liquid in the packaging industry. According to the method of the invention the sterilization liquid is transferred from a supply of sterilization liquid to a buffer tank and the sterilization liq- uid is transferred from the buffer tank to the tub, the tub being self-draining for returning the sterilization liquid to the buffer tank when the web is kept still in the tub. By this method it is ensured that the tub is emptied during stops, without mixing new and used sterilization liquid. In one variant of the inventive method, the sterilization liquid is returned from the tub to the buffer tank when sterilization liquid is not being transferred to the tub. Thus, it may be ensured that the tub is emptied in case of power failure. The sterilization liquid is preferably continuously returned from the tub to the buffer tank as long as there is sterilization liquid in the tub. This makes it possible to ensure reliable emptying of the tub, regardless of the reason for the stop of the machine. In a preferred variant of the method of the invention, the sterilization liquid is transferred from the supply to the buffer tank before sterilization starts, a first pump pumps the sterilization liquid from the buffer tank to the tub during sterilization and the sterilization liquid drains back into the buffer tank when the first pump stops. When this method is used, no sterilization liquid need be transferred from the supply during sterilization and the tub is reliably emptied even in case of power failure. The sterilization liquid is preferably drained by gravity from the tub to the buffer tank through at least one hole at the bottom of the tub when the first pump stops. Reliable emptying is thus ensured using a minimum of moving parts, regardless of the cause of the stop. In a preferred variant of the inventive method, the sterilization liquid is hydrogen peroxide. Hydrogen peroxide is a suitable and reliable sterilization liquid for sterilizing packaging material. 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 preferred embodiment of the invention. Fig. 1 is a perspective view of an apparatus according to the invention. Fig. 2 is a sectional view of the apparatus of Fig. 1 with a web of material passing through it. Detailed Description of Preferred Embodiments of the Invention In Figs 1 and 2 a sterilization apparatus 1 is shown, through which a web 2 of packaging material is passed. At the entrance 3 of the apparatus 1 the web 2, originating from a roll of material (not shown), enters the apparatus 1 and at the exit 4 of the apparatus 1 the web 2 leaves the sterilization apparatus 1 to enter a dryer (not shown). The sterilization apparatus 1 is divided into two main parts, a lower buffer tank 5 and an upper tub 6. An inlet pipe 7 connects the buffer tank 5 to a container 16 (shown only in Fig. 2) in which hydrogen peroxide is delivered to the plant where the sterilization apparatus 1 is used. The buffer tank 5 may be emptied via an outlet pipe 8 connected to a waste container (not shown). A first pump 9 is connected to the buffer tank 5 and the tub 6 for pumping hydrogen peroxide from the buffer tank 5 to the tub 6. In the bottom 10 of the tub 6 there are two small holes 11, of which only one is shown in Fig. 2, for draining hydrogen peroxide from the tub 6 back into the buffer tank 6. The web 2 is passed over two web rollers 12 to be directed into the tub 6 and down towards the bottom 10 of the tub 6. Just below the exit 4 of the apparatus 1, the web 2 passes between two distribution rollers 13, so called squeegee rollers. The function of the sterilization apparatus 1 will now be described with reference to Fig. 2. Before the packaging machine of which the sterilization apparatus 1 is a part is started, hydrogen peroxide is pumped from the container 16 in which it was delivered by a second pump 17 through the inlet pipe 7 into the buffer tank 5. When the hydrogen peroxide in the buffer tank reaches a predetermined level 14 the second pump 17 is stopped, thus interrupting supply through the inlet pipe7. When the packaging machine starts, the first pump 9 is activated and starts pumping hydrogen peroxide from the buffer tank 5 to the tub 6. The hydrogen peroxide continuously drains back from the tub 6, through the holes 11 in the bottom 10, into the buffer tank 5, but the first pump 9 is regulated to pump hydrogen peroxide into the tub 6 at such a rate that a predetermined level 15 is maintained in the tub 6. The web 2 enters the sterilization apparatus 1 through the entrance 3 and passes over the web rollers 12 through the tub 6. The arrangement of the web rollers 12 and the hydrogen peroxide level 15 in the tub 6 ensure that the web 2 is properly immerged in hydrogen peroxide. After passing through the bath of hydrogen peroxide, the web 2 is directed upwards and passed between the squeegee rollers 13. Hydrogen peroxide that has been deposited on the web 2 is thus evenly distributed over the entire width of the web 2, forming a thin film, so that a reliable sterilization of the entire web 2 may be ensured. After leaving the sterilization apparatus 1 through the exit 4, the web 2 passes into a heating chamber for drying off the hydrogen peroxide. Should the packaging machine stop, e.g. because of a web break or power failure, for a longer or shorter period, the first pump 9 is stopped and hydrogen peroxide is therefore no longer pumped from the buffer tank 5 to the tub 6. The hydrogen peroxide is thus drained out of the tub 6 through the holes 11, back into the buffer tank 5. The operator of the packaging machine is thereby not exposed to the hydrogen peroxide should there be a need for repairs in the tub or for re-threading the web 2 through the tub 6. Since the hydrogen peroxide is drained into the buffer tank 5 and not back to the supply 16, used and new hydrogen peroxide are not mixed. During use in the tub 6, the hydrogen peroxide may be contaminated by paper dust from the web 2 and is also gradually degraded, so that the concentration is lowered. Therefore, the hydrogen peroxide used has to be changed. Used hydrogen peroxide is then drained out of the tub 6 into the buffer tank 5 and from the buffer tank 5 through the outlet pipe 8 to the waste container. New hydrogen peroxide is subsequently pumped by the second pump 17 from the supply 16, through the inlet pipe 7, into the buffer tank 5, up to the predetermined level 14. The packaging machine can then be started again and the first pump 9 starts to pump hydrogen peroxide from the buffer tank 5 into the tub 6. The skilled person realises that a number of modifications of the embodiments described herein are possible without departing from the scope of the invention, which is defined in the appended claims. For instance, the sterilization apparatus 1 has been described using hydrogen peroxide as the sterilization liquid. However, other sterilization liquids may also be used in the apparatus and method of the invention. In the embodiment described, the self-draining property of the tub 6 is achieved by means of holes 11 in the bottom 10 of the tub 6. These holes may also be formed in a portion of a wall of the tub 6 near the bottom 10, so that when the first pump 9 stops, the hydrogen peroxide is not completely drained from the tub 6, but reaches a low enough level that the web 2 is no longer immerged. In this way it is still ensured that hydrogen peroxide is not soaked into the edges of the web 2 during stops. It should, however, be borne in mind that there in this case is still a risk of the operator being exposed to the hydrogen peroxide. Since the holes 11 in the bottom 10 of the tub 6 are constantly open, the first pump 9 has to run continuously in order to maintain the desired level 15 of hydrogen peroxide in the tub 6. In another embodiment, the holes could be covered by spring-loaded lids held down by electromagnets (not shown). The first pump 9 would in that case only have to pump hydrogen peroxide into the tub 6 to the desired level 15 when the packaging machine is started and would then stop. In case the packaging machine were stopped, power to the electromagnets holding the lids closed would be switched off, thus opening the holes for draining the hydrogen peroxide back into the buffer tank by gravity. The electromagnetic closing and the spring-loading of the lids would ensure that the tub is self-draining, even in the case of power failure. The tub 6 need not be placed directly above the buffer tank 5. As long as the bottom of the tub 6 is placed higher than the hydrogen peroxide level in the buffer tank 5, the siphon effect may be used for automatically draining the tub 6. In the embodiment shown two pumps are used, the first pump 9 pumping sterilization liquid from the buffer tank 5 to the tub 6 and the second pump 17 pumping sterilization liquid from the supply container 16 to the buffer tank 6. It is, however, envisaged that the sterilization apparatus of the invention could also be constructed using only one pump. The first pump would in that case be used for pumping sterilization liquid both from the supply container 16 to the buffer tank 5 and from the buffer tank 5 to the tub 6. Switches would in this embodiment be arranged for controlling the direction of pumping. 1. An apparatus for sterilization of a web (2) of packaging material, comprising a tub (6) through which the web is to be passed, a supply (16) of sterilization liquid and a transfer system (5, 7, 9, 17) for transferring sterilization liquid from the supply (16) to the tub (6), characterised in that the transfer system comprises a buffer tank (5) to which sterilization liquid is transferred from the supply (16) and a transfer device (9) for transferring sterilization liquid from the buffer tank (5) to the tub (6), wherein the tub (6) is provided with self-draining means (11) for returning the sterilization liquid to the buffer tank (5) when the web (2) is kept still in the tub (6). 2. An apparatus as claimed in claim 1, wherein the transfer device for transferring sterilization liquid from the buffer tank (5) to the tub (6) is a first pump (9) and wherein the transfer system further comprises a second pump (17) for transferring sterilization liquid from the supply (16) to the buffer tank (5) . 3. An apparatus as claimed in claim 1, wherein the transfer device for transferring sterilization liquid from the buffer tank (5) to the tub (6) is a first pump (9) and wherein the first pump (9) is additionally arranged to transfer sterilization liquid from the supply (16) to the buffer tank (5). 4. An apparatus as claimed in claim 2 or 3, wherein the self-draining means (11) of the tub (6) is arranged to return the sterilization liquid to the buffer tank (5) when the first pump (9) is not pumping sterilization liquid to the tub (6). 5. An apparatus as claimed in any one of the preceding claims, wherein the self-draining means (11) of the tub (6) is arranged to continuously return the sterilization liquid to the buffer tank (5) as long as there is sterilization liquid in the tub (6). 6. An apparatus as claimed in any one of the preced ing claims, wherein the tub (6) is arranged at a higher level than the buffer tank (5) and wherein the self- draining means (11) of the tub (6) is at least one hole . (11) at a bottom (10) of the tub (6) for returning the sterilization liquid to the buffer tank (5) when the web (2) is kept still in the tub (6). 7. An apparatus as claimed in any one of the preced ing claims, further comprising a pair of distribution i rollers (13) arranged downstream of the tub (6) in a direction of travel of the web (2), said rollers (13) being arranged to evenly distribute the sterilization liquid deposited on the web (2). 8. An apparatus as claimed in any one of the preceding claims, further comprising web rollers (12) for directing the web (2) through the tub (6). 9. An apparatus as claimed in any one of the preceding claims, wherein the sterilization liquid is hydrogen peroxide. 10. A method for sterilization of a web (2) of packaging material, wherein the web (2) is passed through a tub (6) containing a sterilization liquid, characterised in that the sterilization liquid is transferred from a supply (16) of sterilization liquid to a buffer tank (5) and that the sterilization liquid is transferred from the buffer tank (5) to the tub (6), the tub (6) being self-draining for returning the sterilization liquid to the buffer tank (5) when the web (2) is kept still in the tub (6). 11. A method as claimed in claim 10, wherein the sterilization liquid is returned from the tub (6) to the buffer tank (5) when sterilization liquid is not being transferred to the tub (6). 12. A method as claimed in claim 10 or 11, wherein the sterilization liquid is continuously returned from the tub (6) to the buffer tank (5) as long as there is sterilization liquid in the tub (6). 13. A method as claimed in any one of claims 10-12, wherein the sterilization liquid is transferred from the supply (16) to the buffer tank (5) before sterilization starts, a first pump (9) pumps the sterilization liquid from the buffer tank (5) to the tub (6) during steriliza tion and the sterilization liquid drains back into the buffer tank (5) when the first pump (9) stops. 14. A method as claimed in claim 13, wherein the sterilization liquid is drained by gravity from the tub (6) to the buffer tank (5) through at least one hole (11) at a bottom (10) of the tub (6) when the first pump (9) stops. 15. A method as claimed in any one of claims 10-14, wherein the sterilization liquid is hydrogen peroxide.

Documents:

1881-CHE-2005 OTHER PATENT DOCUMENT 29-11-2011.pdf

1881-CHE-2005 AMENDED CLAIMS 29-11-2011.pdf

1881-CHE-2005 AMENDED PAGES OF SPECIFICATION 29-11-2011.pdf

1881-CHE-2005 EXAMINATION REPORT REPLY RECIEVED 29-11-2011.pdf

1881-CHE-2005 FORM-3 29-11-2011.pdf

1881-CHE-2005 POWER OF ATTORNEY 29-11-2011.pdf

1881-CHE-2005 CORRESPONDENCE PO.pdf

1881-CHE-2005 FORM-1 29-11-2011.pdf

1881-CHE-2005 FORM-18.pdf

1881-che-2005-abstract image.jpg

1881-che-2005-abstract.pdf

1881-che-2005-claims.pdf

1881-che-2005-correspondnece-others.pdf

1881-che-2005-description(complete).pdf

1881-che-2005-drawings.pdf

1881-che-2005-form 1.pdf

1881-che-2005-form 3.pdf

1881-che-2005-form 5.pdf

1881-che-2005-other-documents.pdf